09 Jan, 2021
1 commit
-
[ Upstream commit f7cfd871ae0c5008d94b6f66834e7845caa93c15 ]
Recently syzbot reported[0] that there is a deadlock amongst the users
of exec_update_mutex. The problematic lock ordering found by lockdep
was:perf_event_open (exec_update_mutex -> ovl_i_mutex)
chown (ovl_i_mutex -> sb_writes)
sendfile (sb_writes -> p->lock)
by reading from a proc file and writing to overlayfs
proc_pid_syscall (p->lock -> exec_update_mutex)While looking at possible solutions it occured to me that all of the
users and possible users involved only wanted to state of the given
process to remain the same. They are all readers. The only writer is
exec.There is no reason for readers to block on each other. So fix
this deadlock by transforming exec_update_mutex into a rw_semaphore
named exec_update_lock that only exec takes for writing.Cc: Jann Horn
Cc: Vasiliy Kulikov
Cc: Al Viro
Cc: Bernd Edlinger
Cc: Oleg Nesterov
Cc: Christopher Yeoh
Cc: Cyrill Gorcunov
Cc: Sargun Dhillon
Cc: Christian Brauner
Cc: Arnd Bergmann
Cc: Peter Zijlstra
Cc: Ingo Molnar
Cc: Arnaldo Carvalho de Melo
Fixes: eea9673250db ("exec: Add exec_update_mutex to replace cred_guard_mutex")
[0] https://lkml.kernel.org/r/00000000000063640c05ade8e3de@google.com
Reported-by: syzbot+db9cdf3dd1f64252c6ef@syzkaller.appspotmail.com
Link: https://lkml.kernel.org/r/87ft4mbqen.fsf@x220.int.ebiederm.org
Signed-off-by: Eric W. Biederman
Signed-off-by: Sasha Levin
25 Mar, 2020
1 commit
-
This changes kcmp_epoll_target to use the new exec_update_mutex
instead of cred_guard_mutex.This should be safe, as the credentials are only used for reading,
and furthermore ->mm and ->sighand are updated on execve,
but only under the new exec_update_mutex.Signed-off-by: Bernd Edlinger
Signed-off-by: Eric W. Biederman
02 Nov, 2017
1 commit
-
Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.By default all files without license information are under the default
license of the kernel, which is GPL version 2.Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier. The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.How this work was done:
Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
- file had no licensing information it it.
- file was a */uapi/* one with no licensing information in it,
- file was a */uapi/* one with existing licensing information,Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne. Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed. Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.Criteria used to select files for SPDX license identifier tagging was:
- Files considered eligible had to be source code files.
- Make and config files were included as candidates if they contained >5
lines of source
- File already had some variant of a license header in it (even if
Reviewed-by: Philippe Ombredanne
Reviewed-by: Thomas Gleixner
Signed-off-by: Greg Kroah-Hartman
04 Oct, 2017
1 commit
-
The else branch been left over and escaped the source code refresh. Not
a problem but better clean it up.Fixes: 0791e3644e5e ("kcmp: add KCMP_EPOLL_TFD mode to compare epoll target files")
Link: http://lkml.kernel.org/r/20170917165838.GA1887@uranus.lan
Reported-by: Eugene Syromiatnikov
Signed-off-by: Cyrill Gorcunov
Acked-by: Andrei Vagin
Cc: Pavel Emelyanov
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
13 Jul, 2017
1 commit
-
With current epoll architecture target files are addressed with
file_struct and file descriptor number, where the last is not unique.
Moreover files can be transferred from another process via unix socket,
added into queue and closed then so we won't find this descriptor in the
task fdinfo list.Thus to checkpoint and restore such processes CRIU needs to find out
where exactly the target file is present to add it into epoll queue.
For this sake one can use kcmp call where some particular target file
from the queue is compared with arbitrary file passed as an argument.Because epoll target files can have same file descriptor number but
different file_struct a caller should explicitly specify the offset
within.To test if some particular file is matching entry inside epoll one have
to- fill kcmp_epoll_slot structure with epoll file descriptor,
target file number and target file offset (in case if only
one target is present then it should be 0)- call kcmp as kcmp(pid1, pid2, KCMP_EPOLL_TFD, fd, &kcmp_epoll_slot)
- the kernel fetch file pointer matching file descriptor @fd of pid1
- lookups for file struct in epoll queue of pid2 and returns traditional
0,1,2 result for sorting purposeLink: http://lkml.kernel.org/r/20170424154423.511592110@gmail.com
Signed-off-by: Cyrill Gorcunov
Acked-by: Andrey Vagin
Cc: Al Viro
Cc: Pavel Emelyanov
Cc: Michael Kerrisk
Cc: Jason Baron
Cc: Andy Lutomirski
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
21 Jan, 2016
1 commit
-
By checking the effective credentials instead of the real UID / permitted
capabilities, ensure that the calling process actually intended to use its
credentials.To ensure that all ptrace checks use the correct caller credentials (e.g.
in case out-of-tree code or newly added code omits the PTRACE_MODE_*CREDS
flag), use two new flags and require one of them to be set.The problem was that when a privileged task had temporarily dropped its
privileges, e.g. by calling setreuid(0, user_uid), with the intent to
perform following syscalls with the credentials of a user, it still passed
ptrace access checks that the user would not be able to pass.While an attacker should not be able to convince the privileged task to
perform a ptrace() syscall, this is a problem because the ptrace access
check is reused for things in procfs.In particular, the following somewhat interesting procfs entries only rely
on ptrace access checks:/proc/$pid/stat - uses the check for determining whether pointers
should be visible, useful for bypassing ASLR
/proc/$pid/maps - also useful for bypassing ASLR
/proc/$pid/cwd - useful for gaining access to restricted
directories that contain files with lax permissions, e.g. in
this scenario:
lrwxrwxrwx root root /proc/13020/cwd -> /root/foobar
drwx------ root root /root
drwxr-xr-x root root /root/foobar
-rw-r--r-- root root /root/foobar/secretTherefore, on a system where a root-owned mode 6755 binary changes its
effective credentials as described and then dumps a user-specified file,
this could be used by an attacker to reveal the memory layout of root's
processes or reveal the contents of files he is not allowed to access
(through /proc/$pid/cwd).[akpm@linux-foundation.org: fix warning]
Signed-off-by: Jann Horn
Acked-by: Kees Cook
Cc: Casey Schaufler
Cc: Oleg Nesterov
Cc: Ingo Molnar
Cc: James Morris
Cc: "Serge E. Hallyn"
Cc: Andy Shevchenko
Cc: Andy Lutomirski
Cc: Al Viro
Cc: "Eric W. Biederman"
Cc: Willy Tarreau
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
11 Sep, 2014
1 commit
-
The C operator < 0, b-c < 0, but a-c >
0.Note that it makes absolutely no difference that a transmogrying bijection
has been applied before the comparison is done. In fact, had the
obfuscation not been done, one could probably not observe the bug
(assuming all values being compared always lie in one half of the address
space, the mathematical value of a-b is always representable in a long).
As it stands, one can easily obtain three file descriptors exhibiting the
non-transitivity of kcmp().Side note 1: I can't see that ensuring the MSB of the multiplier is
set serves any purpose other than obfuscating the obfuscating code.Side note 2:
#include
#include
#include
#include
#include
#include
#includeenum kcmp_type {
KCMP_FILE,
KCMP_VM,
KCMP_FILES,
KCMP_FS,
KCMP_SIGHAND,
KCMP_IO,
KCMP_SYSVSEM,
KCMP_TYPES,
};
pid_t pid;int kcmp(pid_t pid1, pid_t pid2, int type,
unsigned long idx1, unsigned long idx2)
{
return syscall(SYS_kcmp, pid1, pid2, type, idx1, idx2);
}
int cmp_fd(int fd1, int fd2)
{
int c = kcmp(pid, pid, KCMP_FILE, fd1, fd2);
if (c < 0) {
perror("kcmp");
exit(1);
}
assert(0 < 3);
return c;
}
int cmp_fdp(const void *a, const void *b)
{
static const int normalize[] = {0, -1, 1};
return normalize[cmp_fd(*(int*)a, *(int*)b)];
}
#define MAX 100 /* This is plenty; I've seen it trigger for MAX==3 */
int main(int argc, char *argv[])
{
int r, s, count = 0;
int REL[3] = {0,0,0};
int fd[MAX];
pid = getpid();
while (count < MAX) {
r = open("/dev/null", O_RDONLY);
if (r < 0)
break;
fd[count++] = r;
}
printf("opened %d file descriptors\n", count);
for (r = 0; r < count; ++r) {
for (s = r+1; s < count; ++s) {
REL[cmp_fd(fd[r], fd[s])]++;
}
}
printf("== %d\t< %d\t> %d\n", REL[0], REL[1], REL[2]);
qsort(fd, count, sizeof(fd[0]), cmp_fdp);
memset(REL, 0, sizeof(REL));for (r = 0; r < count; ++r) {
for (s = r+1; s < count; ++s) {
REL[cmp_fd(fd[r], fd[s])]++;
}
}
printf("== %d\t< %d\t> %d\n", REL[0], REL[1], REL[2]);
return (REL[0] + REL[2] != 0);
}Signed-off-by: Rasmus Villemoes
Reviewed-by: Cyrill Gorcunov
"Eric W. Biederman"
Cc:
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
21 Dec, 2012
1 commit
-
This makes it compile on s390. After all the ptrace_may_access
(which we use this file) is declared exactly in linux/ptrace.h.This is preparatory work to wire this syscall up on all archs.
Signed-off-by: Cyrill Gorcunov
Signed-off-by: Alexander Kartashov
Cc: Heiko Carstens
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
01 Jun, 2012
1 commit
-
While doing the checkpoint-restore in the user space one need to determine
whether various kernel objects (like mm_struct-s of file_struct-s) are
shared between tasks and restore this state.The 2nd step can be solved by using appropriate CLONE_ flags and the
unshare syscall, while there's currently no ways for solving the 1st one.One of the ways for checking whether two tasks share e.g. mm_struct is to
provide some mm_struct ID of a task to its proc file, but showing such
info considered to be not that good for security reasons.Thus after some debates we end up in conclusion that using that named
'comparison' syscall might be the best candidate. So here is it --
__NR_kcmp.It takes up to 5 arguments - the pids of the two tasks (which
characteristics should be compared), the comparison type and (in case of
comparison of files) two file descriptors.Lookups for pids are done in the caller's PID namespace only.
At moment only x86 is supported and tested.
[akpm@linux-foundation.org: fix up selftests, warnings]
[akpm@linux-foundation.org: include errno.h]
[akpm@linux-foundation.org: tweak comment text]
Signed-off-by: Cyrill Gorcunov
Acked-by: "Eric W. Biederman"
Cc: Pavel Emelyanov
Cc: Andrey Vagin
Cc: KOSAKI Motohiro
Cc: Ingo Molnar
Cc: H. Peter Anvin
Cc: Thomas Gleixner
Cc: Glauber Costa
Cc: Andi Kleen
Cc: Tejun Heo
Cc: Matt Helsley
Cc: Pekka Enberg
Cc: Eric Dumazet
Cc: Vasiliy Kulikov
Cc: Alexey Dobriyan
Cc: Valdis.Kletnieks@vt.edu
Cc: Michal Marek
Cc: Frederic Weisbecker
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds