13 Aug, 2020
5 commits
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After the cleanup of page fault accounting, gup does not need to pass
task_struct around any more. Remove that parameter in the whole gup
stack.Signed-off-by: Peter Xu
Signed-off-by: Andrew Morton
Reviewed-by: John Hubbard
Link: http://lkml.kernel.org/r/20200707225021.200906-26-peterx@redhat.com
Signed-off-by: Linus Torvalds -
The path_noexec() check, like the regular file check, was happening too
late, letting LSMs see impossible execve()s. Check it earlier as well in
may_open() and collect the redundant fs/exec.c path_noexec() test under
the same robustness comment as the S_ISREG() check.My notes on the call path, and related arguments, checks, etc:
do_open_execat()
struct open_flags open_exec_flags = {
.open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
.acc_mode = MAY_EXEC,
...
do_filp_open(dfd, filename, open_flags)
path_openat(nameidata, open_flags, flags)
file = alloc_empty_file(open_flags, current_cred());
do_open(nameidata, file, open_flags)
may_open(path, acc_mode, open_flag)
/* new location of MAY_EXEC vs path_noexec() test */
inode_permission(inode, MAY_OPEN | acc_mode)
security_inode_permission(inode, acc_mode)
vfs_open(path, file)
do_dentry_open(file, path->dentry->d_inode, open)
security_file_open(f)
open()
/* old location of path_noexec() test */Signed-off-by: Kees Cook
Signed-off-by: Andrew Morton
Cc: Alexander Viro
Cc: Aleksa Sarai
Cc: Christian Brauner
Cc: Dmitry Vyukov
Cc: Eric Biggers
Cc: Tetsuo Handa
Link: http://lkml.kernel.org/r/20200605160013.3954297-4-keescook@chromium.org
Signed-off-by: Linus Torvalds -
The execve(2)/uselib(2) syscalls have always rejected non-regular files.
Recently, it was noticed that a deadlock was introduced when trying to
execute pipes, as the S_ISREG() test was happening too late. This was
fixed in commit 73601ea5b7b1 ("fs/open.c: allow opening only regular files
during execve()"), but it was added after inode_permission() had already
run, which meant LSMs could see bogus attempts to execute non-regular
files.Move the test into the other inode type checks (which already look for
other pathological conditions[1]). Since there is no need to use
FMODE_EXEC while we still have access to "acc_mode", also switch the test
to MAY_EXEC.Also include a comment with the redundant S_ISREG() checks at the end of
execve(2)/uselib(2) to note that they are present to avoid any mistakes.My notes on the call path, and related arguments, checks, etc:
do_open_execat()
struct open_flags open_exec_flags = {
.open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
.acc_mode = MAY_EXEC,
...
do_filp_open(dfd, filename, open_flags)
path_openat(nameidata, open_flags, flags)
file = alloc_empty_file(open_flags, current_cred());
do_open(nameidata, file, open_flags)
may_open(path, acc_mode, open_flag)
/* new location of MAY_EXEC vs S_ISREG() test */
inode_permission(inode, MAY_OPEN | acc_mode)
security_inode_permission(inode, acc_mode)
vfs_open(path, file)
do_dentry_open(file, path->dentry->d_inode, open)
/* old location of FMODE_EXEC vs S_ISREG() test */
security_file_open(f)
open()[1] https://lore.kernel.org/lkml/202006041910.9EF0C602@keescook/
Signed-off-by: Kees Cook
Signed-off-by: Andrew Morton
Cc: Aleksa Sarai
Cc: Alexander Viro
Cc: Christian Brauner
Cc: Dmitry Vyukov
Cc: Eric Biggers
Cc: Tetsuo Handa
Link: http://lkml.kernel.org/r/20200605160013.3954297-3-keescook@chromium.org
Signed-off-by: Linus Torvalds -
Patch series "Relocate execve() sanity checks", v2.
While looking at the code paths for the proposed O_MAYEXEC flag, I saw
some things that looked like they should be fixed up.exec: Change uselib(2) IS_SREG() failure to EACCES
This just regularizes the return code on uselib(2).exec: Move S_ISREG() check earlier
This moves the S_ISREG() check even earlier than it was already.exec: Move path_noexec() check earlier
This adds the path_noexec() check to the same place as the
S_ISREG() check.This patch (of 3):
Change uselib(2)' S_ISREG() error return to EACCES instead of EINVAL so
the behavior matches execve(2), and the seemingly documented value. The
"not a regular file" failure mode of execve(2) is explicitly
documented[1], but it is not mentioned in uselib(2)[2] which does,
however, say that open(2) and mmap(2) errors may apply. The documentation
for open(2) does not include a "not a regular file" error[3], but mmap(2)
does[4], and it is EACCES.[1] http://man7.org/linux/man-pages/man2/execve.2.html#ERRORS
[2] http://man7.org/linux/man-pages/man2/uselib.2.html#ERRORS
[3] http://man7.org/linux/man-pages/man2/open.2.html#ERRORS
[4] http://man7.org/linux/man-pages/man2/mmap.2.html#ERRORSSigned-off-by: Kees Cook
Signed-off-by: Andrew Morton
Acked-by: Christian Brauner
Cc: Aleksa Sarai
Cc: Alexander Viro
Cc: Dmitry Vyukov
Cc: Eric Biggers
Cc: Tetsuo Handa
Link: http://lkml.kernel.org/r/20200605160013.3954297-1-keescook@chromium.org
Link: http://lkml.kernel.org/r/20200605160013.3954297-2-keescook@chromium.org
Signed-off-by: Linus Torvalds -
Both exec and exit want to ensure that the uaccess routines actually do
access user pointers. Use the newly added force_uaccess_begin helper
instead of an open coded set_fs for that to prepare for kernel builds
where set_fs() does not exist.Signed-off-by: Christoph Hellwig
Signed-off-by: Andrew Morton
Acked-by: Linus Torvalds
Cc: Nick Hu
Cc: Greentime Hu
Cc: Vincent Chen
Cc: Paul Walmsley
Cc: Palmer Dabbelt
Cc: Geert Uytterhoeven
Link: http://lkml.kernel.org/r/20200710135706.537715-7-hch@lst.de
Signed-off-by: Linus Torvalds
21 Jul, 2020
6 commits
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To allow the kernel not to play games with set_fs to call exec
implement kernel_execve. The function kernel_execve takes pointers
into kernel memory and copies the values pointed to onto the new
userspace stack.The calls with arguments from kernel space of do_execve are replaced
with calls to kernel_execve.The calls do_execve and do_execveat are made static as there are now
no callers outside of exec.The comments that mention do_execve are updated to refer to
kernel_execve or execve depending on the circumstances. In addition
to correcting the comments, this makes it easy to grep for do_execve
and verify it is not used.Inspired-by: https://lkml.kernel.org/r/20200627072704.2447163-1-hch@lst.de
Reviewed-by: Kees Cook
Link: https://lkml.kernel.org/r/87wo365ikj.fsf@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" -
In preparation for implementiong kernel_execve (which will take kernel
pointers not userspace pointers) factor out bprm_stack_limits out of
prepare_arg_pages. This separates the counting which depends upon the
getting data from userspace from the calculations of the stack limits
which is usable in kernel_execve.The remove prepare_args_pages and compute bprm->argc and bprm->envc
directly in do_execveat_common, before bprm_stack_limits is called.Reviewed-by: Kees Cook
Reviewed-by: Christoph Hellwig
Link: https://lkml.kernel.org/r/87365u6x60.fsf@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" -
Currently it is necessary for the usermode helper code and the code
that launches init to use set_fs so that pages coming from the kernel
look like they are coming from userspace.To allow that usage of set_fs to be removed cleanly the argument
copying from userspace needs to happen earlier. Factor bprm_execve
out of do_execve_common to separate out the copying of arguments
to the newe stack, and the rest of exec.In separating bprm_execve from do_execve_common the copying
of the arguments onto the new stack happens earlier.As the copying of the arguments does not depend any security hooks,
files, the file table, current->in_execve, current->fs->in_exec,
bprm->unsafe, or creds this is safe.Likewise the security hook security_creds_for_exec does not depend upon
preventing the argument copying from happening.In addition to making it possible to implement kernel_execve that
performs the copying differently, this separation of bprm_execve from
do_execve_common makes for a nice separation of responsibilities making
the exec code easier to navigate.Reviewed-by: Kees Cook
Reviewed-by: Christoph Hellwig
Link: https://lkml.kernel.org/r/878sfm6x6x.fsf@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" -
Currently it is necessary for the usermode helper code and the code that
launches init to use set_fs so that pages coming from the kernel look like
they are coming from userspace.To allow that usage of set_fs to be removed cleanly the argument copying
from userspace needs to happen earlier. Move the allocation and
initialization of bprm->mm into alloc_bprm so that the bprm->mm is
available early to store the new user stack into. This is a prerequisite
for copying argv and envp into the new user stack early before ther rest of
exec.To keep the things consistent the cleanup of bprm->mm is moved into
free_bprm. So that bprm->mm will be cleaned up whenever bprm->mm is
allocated and free_bprm are called.Moving bprm_mm_init earlier is safe as it does not depend on any files,
current->in_execve, current->fs->in_exec, bprm->unsafe, or the if the file
table is shared. (AKA bprm_mm_init does not depend on any of the code that
happens between alloc_bprm and where it was previously called.)This moves bprm->mm cleanup after current->fs->in_exec is set to 0. This
is safe because current->fs->in_exec is only used to preventy taking an
additional reference on the fs_struct.This moves bprm->mm cleanup after current->in_execve is set to 0. This is
safe because current->in_execve is only used by the lsms (apparmor and
tomoyou) and always for LSM specific functions, never for anything to do
with the mm.This adds bprm->mm cleanup into the successful return path. This is safe
because being on the successful return path implies that begin_new_exec
succeeded and set brpm->mm to NULL. As bprm->mm is NULL bprm cleanup I am
moving into free_bprm will do nothing.Reviewed-by: Kees Cook
Reviewed-by: Christoph Hellwig
Link: https://lkml.kernel.org/r/87eepe6x7p.fsf@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" -
Currently it is necessary for the usermode helper code and the code
that launches init to use set_fs so that pages coming from the kernel
look like they are coming from userspace.To allow that usage of set_fs to be removed cleanly the argument
copying from userspace needs to happen earlier. Move the computation
of bprm->filename and possible allocation of a name in the case
of execveat into alloc_bprm to make that possible.The exectuable name, the arguments, and the environment are
copied into the new usermode stack which is stored in bprm
until exec passes the point of no return.As the executable name is copied first onto the usermode stack
it needs to be known. As there are no dependencies to computing
the executable name, compute it early in alloc_bprm.As an implementation detail if the filename needs to be generated
because it embeds a file descriptor store that filename in a new field
bprm->fdpath, and free it in free_bprm. Previously this was done in
an independent variable pathbuf. I have renamed pathbuf fdpath
because fdpath is more suggestive of what kind of path is in the
variable. I moved fdpath into struct linux_binprm because it is
tightly tied to the other variables in struct linux_binprm, and as
such is needed to allow the call alloc_binprm to move.Reviewed-by: Kees Cook
Reviewed-by: Christoph Hellwig
Link: https://lkml.kernel.org/r/87k0z66x8f.fsf@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" -
Currently it is necessary for the usermode helper code and the code
that launches init to use set_fs so that pages coming from the kernel
look like they are coming from userspace.To allow that usage of set_fs to be removed cleanly the argument
copying from userspace needs to happen earlier. Move the allocation
of the bprm into it's own function (alloc_bprm) and move the call of
alloc_bprm before unshare_files so that bprm can ultimately be
allocated, the arguments can be placed on the new stack, and then the
bprm can be passed into the core of exec.Neither the allocation of struct binprm nor the unsharing depend upon each
other so swapping the order in which they are called is trivially safe.To keep things consistent the order of cleanup at the end of
do_execve_common swapped to match the order of initialization.Reviewed-by: Kees Cook
Link: https://lkml.kernel.org/r/87pn8y6x9a.fsf@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman"
04 Jul, 2020
1 commit
-
Now that the last callser has been removed remove this code from exec.
For anyone thinking of resurrecing do_execve_file please note that
the code was buggy in several fundamental ways.- It did not ensure the file it was passed was read-only and that
deny_write_access had been called on it. Which subtlely breaks
invaniants in exec.- The caller of do_execve_file was expected to hold and put a
reference to the file, but an extra reference for use by exec was
not taken so that when exec put it's reference to the file an
underflow occured on the file reference count.- The point of the interface was so that a pathname did not need to
exist. Which breaks pathname based LSMs.Tetsuo Handa originally reported these issues[1]. While it was clear
that deny_write_access was missing the fundamental incompatibility
with the passed in O_RDWR filehandle was not immediately recognized.All of these issues were fixed by modifying the usermode driver code
to have a path, so it did not need this hack.Reported-by: Tetsuo Handa
[1] https://lore.kernel.org/linux-fsdevel/2a8775b4-1dd5-9d5c-aa42-9872445e0942@i-love.sakura.ne.jp/
v1: https://lkml.kernel.org/r/871rm2f0hi.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87lfk54p0m.fsf_-_@x220.int.ebiederm.org
Link: https://lkml.kernel.org/r/20200702164140.4468-10-ebiederm@xmission.com
Reviewed-by: Greg Kroah-Hartman
Acked-by: Alexei Starovoitov
Tested-by: Alexei Starovoitov
Signed-off-by: "Eric W. Biederman"
10 Jun, 2020
2 commits
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Convert comments that reference mmap_sem to reference mmap_lock instead.
[akpm@linux-foundation.org: fix up linux-next leftovers]
[akpm@linux-foundation.org: s/lockaphore/lock/, per Vlastimil]
[akpm@linux-foundation.org: more linux-next fixups, per Michel]Signed-off-by: Michel Lespinasse
Signed-off-by: Andrew Morton
Reviewed-by: Vlastimil Babka
Reviewed-by: Daniel Jordan
Cc: Davidlohr Bueso
Cc: David Rientjes
Cc: Hugh Dickins
Cc: Jason Gunthorpe
Cc: Jerome Glisse
Cc: John Hubbard
Cc: Laurent Dufour
Cc: Liam Howlett
Cc: Matthew Wilcox
Cc: Peter Zijlstra
Cc: Ying Han
Link: http://lkml.kernel.org/r/20200520052908.204642-13-walken@google.com
Signed-off-by: Linus Torvalds -
This change converts the existing mmap_sem rwsem calls to use the new mmap
locking API instead.The change is generated using coccinelle with the following rule:
// spatch --sp-file mmap_lock_api.cocci --in-place --include-headers --dir .
@@
expression mm;
@@
(
-init_rwsem
+mmap_init_lock
|
-down_write
+mmap_write_lock
|
-down_write_killable
+mmap_write_lock_killable
|
-down_write_trylock
+mmap_write_trylock
|
-up_write
+mmap_write_unlock
|
-downgrade_write
+mmap_write_downgrade
|
-down_read
+mmap_read_lock
|
-down_read_killable
+mmap_read_lock_killable
|
-down_read_trylock
+mmap_read_trylock
|
-up_read
+mmap_read_unlock
)
-(&mm->mmap_sem)
+(mm)Signed-off-by: Michel Lespinasse
Signed-off-by: Andrew Morton
Reviewed-by: Daniel Jordan
Reviewed-by: Laurent Dufour
Reviewed-by: Vlastimil Babka
Cc: Davidlohr Bueso
Cc: David Rientjes
Cc: Hugh Dickins
Cc: Jason Gunthorpe
Cc: Jerome Glisse
Cc: John Hubbard
Cc: Liam Howlett
Cc: Matthew Wilcox
Cc: Peter Zijlstra
Cc: Ying Han
Link: http://lkml.kernel.org/r/20200520052908.204642-5-walken@google.com
Signed-off-by: Linus Torvalds
09 Jun, 2020
2 commits
-
read_code operates on user addresses.
Signed-off-by: Christoph Hellwig
Signed-off-by: Andrew Morton
Cc: Alexander Viro
Link: http://lkml.kernel.org/r/20200515143646.3857579-27-hch@lst.de
Signed-off-by: Linus Torvalds -
Only build read_code when binary formats that use it are built into the
kernel.Signed-off-by: Christoph Hellwig
Signed-off-by: Andrew Morton
Cc: Alexander Viro
Link: http://lkml.kernel.org/r/20200515143646.3857579-26-hch@lst.de
Signed-off-by: Linus Torvalds
05 Jun, 2020
5 commits
-
Merge yet more updates from Andrew Morton:
- More MM work. 100ish more to go. Mike Rapoport's "mm: remove
__ARCH_HAS_5LEVEL_HACK" series should fix the current ppc issue- Various other little subsystems
* emailed patches from Andrew Morton : (127 commits)
lib/ubsan.c: fix gcc-10 warnings
tools/testing/selftests/vm: remove duplicate headers
selftests: vm: pkeys: fix multilib builds for x86
selftests: vm: pkeys: use the correct page size on powerpc
selftests/vm/pkeys: override access right definitions on powerpc
selftests/vm/pkeys: test correct behaviour of pkey-0
selftests/vm/pkeys: introduce a sub-page allocator
selftests/vm/pkeys: detect write violation on a mapped access-denied-key page
selftests/vm/pkeys: associate key on a mapped page and detect write violation
selftests/vm/pkeys: associate key on a mapped page and detect access violation
selftests/vm/pkeys: improve checks to determine pkey support
selftests/vm/pkeys: fix assertion in test_pkey_alloc_exhaust()
selftests/vm/pkeys: fix number of reserved powerpc pkeys
selftests/vm/pkeys: introduce powerpc support
selftests/vm/pkeys: introduce generic pkey abstractions
selftests: vm: pkeys: use the correct huge page size
selftests/vm/pkeys: fix alloc_random_pkey() to make it really random
selftests/vm/pkeys: fix assertion in pkey_disable_set/clear()
selftests/vm/pkeys: fix pkey_disable_clear()
selftests: vm: pkeys: add helpers for pkey bits
... -
Currently copy_string_kernel is just a wrapper around copy_strings that
simplifies the calling conventions and uses set_fs to allow passing a
kernel pointer. But due to the fact the we only need to handle a single
kernel argument pointer, the logic can be sigificantly simplified while
getting rid of the set_fs.Signed-off-by: Christoph Hellwig
Signed-off-by: Andrew Morton
Cc: Alexander Viro
Link: http://lkml.kernel.org/r/20200501104105.2621149-3-hch@lst.de
Signed-off-by: Linus Torvalds -
copy_strings_kernel is always used with a single argument,
adjust the calling convention to that.Signed-off-by: Christoph Hellwig
Signed-off-by: Andrew Morton
Cc: Alexander Viro
Link: http://lkml.kernel.org/r/20200501104105.2621149-2-hch@lst.de
Signed-off-by: Linus Torvalds -
Pull execve updates from Eric Biederman:
"Last cycle for the Nth time I ran into bugs and quality of
implementation issues related to exec that could not be easily be
fixed because of the way exec is implemented. So I have been digging
into exec and cleanup up what I can.I don't think I have exec sorted out enough to fix the issues I
started with but I have made some headway this cycle with 4 sets of
changes.- promised cleanups after introducing exec_update_mutex
- trivial cleanups for exec
- control flow simplifications
- remove the recomputation of bprm->cred
The net result is code that is a bit easier to understand and work
with and a decrease in the number of lines of code (if you don't count
the added tests)"* 'exec-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: (24 commits)
exec: Compute file based creds only once
exec: Add a per bprm->file version of per_clear
binfmt_elf_fdpic: fix execfd build regression
selftests/exec: Add binfmt_script regression test
exec: Remove recursion from search_binary_handler
exec: Generic execfd support
exec/binfmt_script: Don't modify bprm->buf and then return -ENOEXEC
exec: Move the call of prepare_binprm into search_binary_handler
exec: Allow load_misc_binary to call prepare_binprm unconditionally
exec: Convert security_bprm_set_creds into security_bprm_repopulate_creds
exec: Factor security_bprm_creds_for_exec out of security_bprm_set_creds
exec: Teach prepare_exec_creds how exec treats uids & gids
exec: Set the point of no return sooner
exec: Move handling of the point of no return to the top level
exec: Run sync_mm_rss before taking exec_update_mutex
exec: Fix spelling of search_binary_handler in a comment
exec: Move the comment from above de_thread to above unshare_sighand
exec: Rename flush_old_exec begin_new_exec
exec: Move most of setup_new_exec into flush_old_exec
exec: In setup_new_exec cache current in the local variable me
... -
Pull proc updates from Eric Biederman:
"This has four sets of changes:- modernize proc to support multiple private instances
- ensure we see the exit of each process tid exactly
- remove has_group_leader_pid
- use pids not tasks in posix-cpu-timers lookup
Alexey updated proc so each mount of proc uses a new superblock. This
allows people to actually use mount options with proc with no fear of
messing up another mount of proc. Given the kernel's internal mounts
of proc for things like uml this was a real problem, and resulted in
Android's hidepid mount options being ignored and introducing security
issues.The rest of the changes are small cleanups and fixes that came out of
my work to allow this change to proc. In essence it is swapping the
pids in de_thread during exec which removes a special case the code
had to handle. Then updating the code to stop handling that special
case"* 'proc-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
proc: proc_pid_ns takes super_block as an argument
remove the no longer needed pid_alive() check in __task_pid_nr_ns()
posix-cpu-timers: Replace __get_task_for_clock with pid_for_clock
posix-cpu-timers: Replace cpu_timer_pid_type with clock_pid_type
posix-cpu-timers: Extend rcu_read_lock removing task_struct references
signal: Remove has_group_leader_pid
exec: Remove BUG_ON(has_group_leader_pid)
posix-cpu-timer: Unify the now redundant code in lookup_task
posix-cpu-timer: Tidy up group_leader logic in lookup_task
proc: Ensure we see the exit of each process tid exactly once
rculist: Add hlists_swap_heads_rcu
proc: Use PIDTYPE_TGID in next_tgid
Use proc_pid_ns() to get pid_namespace from the proc superblock
proc: use named enums for better readability
proc: use human-readable values for hidepid
docs: proc: add documentation for "hidepid=4" and "subset=pid" options and new mount behavior
proc: add option to mount only a pids subset
proc: instantiate only pids that we can ptrace on 'hidepid=4' mount option
proc: allow to mount many instances of proc in one pid namespace
proc: rename struct proc_fs_info to proc_fs_opts
30 May, 2020
2 commits
-
Move the computation of creds from prepare_binfmt into begin_new_exec
so that the creds need only be computed once. This is just code
reorganization no semantic changes of any kind are made.Moving the computation is safe. I have looked through the kernel and
verified none of the binfmts look at bprm->cred directly, and that
there are no helpers that look at bprm->cred indirectly. Which means
that it is not a problem to compute the bprm->cred later in the
execution flow as it is not used until it becomes current->cred.A new function bprm_creds_from_file is added to contain the work that
needs to be done. bprm_creds_from_file first computes which file
bprm->executable or most likely bprm->file that the bprm->creds
will be computed from.The funciton bprm_fill_uid is updated to receive the file instead of
accessing bprm->file. The now unnecessary work needed to reset the
bprm->cred->euid, and bprm->cred->egid is removed from brpm_fill_uid.
A small comment to document that bprm_fill_uid now only deals with the
work to handle suid and sgid files. The default case is already
heandled by prepare_exec_creds.The function security_bprm_repopulate_creds is renamed
security_bprm_creds_from_file and now is explicitly passed the file
from which to compute the creds. The documentation of the
bprm_creds_from_file security hook is updated to explain when the hook
is called and what it needs to do. The file is passed from
cap_bprm_creds_from_file into get_file_caps so that the caps are
computed for the appropriate file. The now unnecessary work in
cap_bprm_creds_from_file to reset the ambient capabilites has been
removed. A small comment to document that the work of
cap_bprm_creds_from_file is to read capabilities from the files
secureity attribute and derive capabilities from the fact the
user had uid 0 has been added.Reviewed-by: Kees Cook
Signed-off-by: "Eric W. Biederman" -
There is a small bug in the code that recomputes parts of bprm->cred
for every bprm->file. The code never recomputes the part of
clear_dangerous_personality_flags it is responsible for.Which means that in practice if someone creates a sgid script
the interpreter will not be able to use any of:
READ_IMPLIES_EXEC
ADDR_NO_RANDOMIZE
ADDR_COMPAT_LAYOUT
MMAP_PAGE_ZERO.This accentially clearing of personality flags probably does
not matter in practice because no one has complained
but it does make the code more difficult to understand.Further remaining bug compatible prevents the recomputation from being
removed and replaced by simply computing bprm->cred once from the
final bprm->file.Making this change removes the last behavior difference between
computing bprm->creds from the final file and recomputing
bprm->cred several times. Which allows this behavior change
to be justified for it's own reasons, and for any but hunts
looking into why the behavior changed to wind up here instead
of in the code that will follow that computes bprm->cred
from the final bprm->file.This small logic bug appears to have existed since the code
started clearing dangerous personality bits.History Tree: git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Fixes: 1bb0fa189c6a ("[PATCH] NX: clean up legacy binary support")
Reviewed-by: Kees Cook
Signed-off-by: "Eric W. Biederman"
21 May, 2020
6 commits
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Recursion in kernel code is generally a bad idea as it can overflow
the kernel stack. Recursion in exec also hides that the code is
looping and that the loop changes bprm->file.Instead of recursing in search_binary_handler have the methods that
would recurse set bprm->interpreter and return 0. Modify exec_binprm
to loop when bprm->interpreter is set. Consolidate all of the
reassignments of bprm->file in that loop to make it clear what is
going on.The structure of the new loop in exec_binprm is that all errors return
immediately, while successful completion (ret == 0 &&
!bprm->interpreter) just breaks out of the loop and runs what
exec_bprm has always run upon successful completion.Fail if the an interpreter is being call after execfd has been set.
The code has never properly handled an interpreter being called with
execfd being set and with reassignments of bprm->file and the
assignment of bprm->executable in generic code it has finally become
possible to test and fail when if this problematic condition happens.With the reassignments of bprm->file and the assignment of
bprm->executable moved into the generic code add a test to see if
bprm->executable is being reassigned.In search_binary_handler remove the test for !bprm->file. With all
reassignments of bprm->file moved to exec_binprm bprm->file can never
be NULL in search_binary_handler.Link: https://lkml.kernel.org/r/87sgfwyd84.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds
Reviewed-by: Kees Cook
Signed-off-by: "Eric W. Biederman" -
Most of the support for passing the file descriptor of an executable
to an interpreter already lives in the generic code and in binfmt_elf.
Rework the fields in binfmt_elf that deal with executable file
descriptor passing to make executable file descriptor passing a first
class concept.Move the fd_install from binfmt_misc into begin_new_exec after the new
creds have been installed. This means that accessing the file through
/proc//fd/N is able to see the creds for the new executable
before allowing access to the new executables files.Performing the install of the executables file descriptor after
the point of no return also means that nothing special needs to
be done on error. The exiting of the process will close all
of it's open files.Move the would_dump from binfmt_misc into begin_new_exec right
after would_dump is called on the bprm->file. This makes it
obvious this case exists and that no nesting of bprm->file is
currently supported.In binfmt_misc the movement of fd_install into generic code means
that it's special error exit path is no longer needed.Link: https://lkml.kernel.org/r/87y2poyd91.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds
Reviewed-by: Kees Cook
Signed-off-by: "Eric W. Biederman" -
The code in prepare_binary_handler needs to be run every time
search_binary_handler is called so move the call into search_binary_handler
itself to make the code simpler and easier to understand.Link: https://lkml.kernel.org/r/87d070zrvx.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds
Reviewed-by: Kees Cook
Reviewed-by: James Morris
Signed-off-by: "Eric W. Biederman" -
Add a flag preserve_creds that binfmt_misc can set to prevent
credentials from being updated. This allows binfmt_misc to always
call prepare_binprm. Allowing the credential computation logic to be
consolidated.Not replacing the credentials with the interpreters credentials is
safe because because an open file descriptor to the executable is
passed to the interpreter. As the interpreter does not need to
reopen the executable it is guaranteed to see the same file that
exec sees.Ref: c407c033de84 ("[PATCH] binfmt_misc: improve calculation of interpreter's credentials")
Link: https://lkml.kernel.org/r/87imgszrwo.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds
Reviewed-by: Kees Cook
Signed-off-by: "Eric W. Biederman" -
Rename bprm->cap_elevated to bprm->active_secureexec and initialize it
in prepare_binprm instead of in cap_bprm_set_creds. Initializing
bprm->active_secureexec in prepare_binprm allows multiple
implementations of security_bprm_repopulate_creds to play nicely with
each other.Rename security_bprm_set_creds to security_bprm_reopulate_creds to
emphasize that this path recomputes part of bprm->cred. This
recomputation avoids the time of check vs time of use problems that
are inherent in unix #! interpreters.In short two renames and a move in the location of initializing
bprm->active_secureexec.Link: https://lkml.kernel.org/r/87o8qkzrxp.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds
Reviewed-by: Kees Cook
Signed-off-by: "Eric W. Biederman" -
Today security_bprm_set_creds has several implementations:
apparmor_bprm_set_creds, cap_bprm_set_creds, selinux_bprm_set_creds,
smack_bprm_set_creds, and tomoyo_bprm_set_creds.Except for cap_bprm_set_creds they all test bprm->called_set_creds and
return immediately if it is true. The function cap_bprm_set_creds
ignores bprm->calld_sed_creds entirely.Create a new LSM hook security_bprm_creds_for_exec that is called just
before prepare_binprm in __do_execve_file, resulting in a LSM hook
that is called exactly once for the entire of exec. Modify the bits
of security_bprm_set_creds that only want to be called once per exec
into security_bprm_creds_for_exec, leaving only cap_bprm_set_creds
behind.Remove bprm->called_set_creds all of it's former users have been moved
to security_bprm_creds_for_exec.Add or upate comments a appropriate to bring them up to date and
to reflect this change.Link: https://lkml.kernel.org/r/87v9kszrzh.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds
Acked-by: Casey Schaufler # For the LSM and Smack bits
Reviewed-by: Kees Cook
Signed-off-by: "Eric W. Biederman"
18 May, 2020
1 commit
-
The change to exec is relevant to the cleanup work I have been doing.
Merge it here so that I can build on top of it, and so hopefully
that other merge logic can pick up on this and see how to deal
with the conflict between that change and my exec cleanup work.Signed-off-by: "Eric W. Biederman"
17 May, 2020
1 commit
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I goofed when I added mm->user_ns support to would_dump. I missed the
fact that in the case of binfmt_loader, binfmt_em86, binfmt_misc, and
binfmt_script bprm->file is reassigned. Which made the move of
would_dump from setup_new_exec to __do_execve_file before exec_binprm
incorrect as it can result in would_dump running on the script instead
of the interpreter of the script.The net result is that the code stopped making unreadable interpreters
undumpable. Which allows them to be ptraced and written to disk
without special permissions. Oops.The move was necessary because the call in set_new_exec was after
bprm->mm was no longer valid.To correct this mistake move the misplaced would_dump from
__do_execve_file into flos_old_exec, before exec_mmap is called.I tested and confirmed that without this fix I can attach with gdb to
a script with an unreadable interpreter, and with this fix I can not.Cc: stable@vger.kernel.org
Fixes: f84df2a6f268 ("exec: Ensure mm->user_ns contains the execed files")
Signed-off-by: "Eric W. Biederman"
12 May, 2020
3 commits
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Make the code more robust by marking the point of no return sooner.
This ensures that future code changes don't need to worry about how
they return errors if they are past this point.This results in no actual change in behavior as __do_execve_file does
not force SIGSEGV when there is a pending fatal signal pending past
the point of no return. Further the only error returns from de_thread
and exec_mmap that can occur result in fatal signals being pending.Reviewed-by: Kees Cook
Link: https://lkml.kernel.org/r/87sgga5klu.fsf_-_@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" -
Move the handing of the point of no return from search_binary_handler
into __do_execve_file so that it is easier to find, and to keep
things robust in the face of change.Make it clear that an existing fatal signal will take precedence over
a forced SIGSEGV by not forcing SIGSEGV if a fatal signal is already
pending. This does not change the behavior but it saves a reader
of the code the tedium of reading and understanding force_sig
and the signal delivery code.Update the comment in begin_new_exec about where SIGSEGV is forced.
Keep point_of_no_return from being a mystery by documenting
what the code is doing where it forces SIGSEGV if the
code is past the point of no return.Reviewed-by: Kees Cook
Link: https://lkml.kernel.org/r/87y2q25knl.fsf_-_@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" -
Like exec_mm_release sync_mm_rss is about flushing out the state of
the old_mm, which does not need to happen under exec_update_mutex.Make this explicit by moving sync_mm_rss outside of exec_update_mutex.
Reviewed-by: Kees Cook
Link: https://lkml.kernel.org/r/875zd66za3.fsf_-_@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman"
09 May, 2020
2 commits
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Link: https://lkml.kernel.org/r/87h7wq6zc1.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Kees Cook
Signed-off-by: "Eric W. Biederman" -
The comment describes work that now happens in unshare_sighand so
move the comment where it makes sense.Link: https://lkml.kernel.org/r/87mu6i6zcs.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Kees Cook
Signed-off-by: "Eric W. Biederman"
08 May, 2020
4 commits
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There is and has been for a very long time been a lot more going on in
flush_old_exec than just flushing the old state. After the movement
of code from setup_new_exec there is a whole lot more going on than
just flushing the old executables state.Rename flush_old_exec to begin_new_exec to more accurately reflect
what this function does.Reviewed-by: Kees Cook
Reviewed-by: Greg Ungerer
Signed-off-by: "Eric W. Biederman" -
The current idiom for the callers is:
flush_old_exec(bprm);
set_personality(...);
setup_new_exec(bprm);In 2010 Linus split flush_old_exec into flush_old_exec and
setup_new_exec. With the intention that setup_new_exec be what is
called after the processes new personality is set.Move the code that doesn't depend upon the personality from
setup_new_exec into flush_old_exec. This is to facilitate future
changes by having as much code together in one function as possible.To see why it is safe to move this code please note that effectively
this change moves the personality setting in the binfmt and the following
three lines of code after everything except unlocking the mutexes:
arch_pick_mmap_layout
arch_setup_new_exec
mm->task_size = TASK_SIZEThe function arch_pick_mmap_layout at most sets:
mm->get_unmapped_area
mm->mmap_base
mm->mmap_legacy_base
mm->mmap_compat_base
mm->mmap_compat_legacy_base
which nothing in flush_old_exec or setup_new_exec depends on.The function arch_setup_new_exec only sets architecture specific
state and the rest of the functions only deal in state that applies
to all architectures.The last line just sets mm->task_size and again nothing in flush_old_exec
or setup_new_exec depend on task_size.Ref: 221af7f87b97 ("Split 'flush_old_exec' into two functions")
Reviewed-by: Kees Cook
Reviewed-by: Greg Ungerer
Signed-off-by: "Eric W. Biederman" -
At least gcc 8.3 when generating code for x86_64 has a hard time
consolidating multiple calls to current aka get_current(), and winds
up unnecessarily rereading %gs:current_task several times in
setup_new_exec.Caching the value of current in the local variable of me generates
slightly better and shorter assembly.Reviewed-by: Kees Cook
Reviewed-by: Greg Ungerer
Signed-off-by: "Eric W. Biederman" -
The two functions are now always called one right after the
other so merge them together to make future maintenance easier.Reviewed-by: Kees Cook
Reviewed-by: Greg Ungerer
Signed-off-by: "Eric W. Biederman"