26 Apr, 2012
1 commit
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- Convert the old uid mapping functions into compatibility wrappers
- Add a uid/gid mapping layer from user space uid and gids to kernel
internal uids and gids that is extent based for simplicty and speed.
* Working with number space after mapping uids/gids into their kernel
internal version adds only mapping complexity over what we have today,
leaving the kernel code easy to understand and test.
- Add proc files /proc/self/uid_map /proc/self/gid_map
These files display the mapping and allow a mapping to be added
if a mapping does not exist.
- Allow entering the user namespace without a uid or gid mapping.
Since we are starting with an existing user our uids and gids
still have global mappings so are still valid and useful they just don't
have local mappings. The requirement for things to work are global uid
and gid so it is odd but perfectly fine not to have a local uid
and gid mapping.
Not requiring global uid and gid mappings greatly simplifies
the logic of setting up the uid and gid mappings by allowing
the mappings to be set after the namespace is created which makes the
slight weirdness worth it.
- Make the mappings in the initial user namespace to the global
uid/gid space explicit. Today it is an identity mapping
but in the future we may want to twist this for debugging, similar
to what we do with jiffies.
- Document the memory ordering requirements of setting the uid and
gid mappings. We only allow the mappings to be set once
and there are no pointers involved so the requirments are
trivial but a little atypical.Performance:
In this scheme for the permission checks the performance is expected to
stay the same as the actuall machine instructions should remain the same.The worst case I could think of is ls -l on a large directory where
all of the stat results need to be translated with from kuids and
kgids to uids and gids. So I benchmarked that case on my laptop
with a dual core hyperthread Intel i5-2520M cpu with 3M of cpu cache.My benchmark consisted of going to single user mode where nothing else
was running. On an ext4 filesystem opening 1,000,000 files and looping
through all of the files 1000 times and calling fstat on the
individuals files. This was to ensure I was benchmarking stat times
where the inodes were in the kernels cache, but the inode values were
not in the processors cache. My results:v3.4-rc1: ~= 156ns (unmodified v3.4-rc1 with user namespace support disabled)
v3.4-rc1-userns-: ~= 155ns (v3.4-rc1 with my user namespace patches and user namespace support disabled)
v3.4-rc1-userns+: ~= 164ns (v3.4-rc1 with my user namespace patches and user namespace support enabled)All of the configurations ran in roughly 120ns when I performed tests
that ran in the cpu cache.So in summary the performance impact is:
1ns improvement in the worst case with user namespace support compiled out.
8ns aka 5% slowdown in the worst case with user namespace support compiled in.Acked-by: Serge Hallyn
Signed-off-by: Eric W. Biederman
08 Apr, 2012
2 commits
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Make it possible to easily switch between strong mandatory
type checks and relaxed type checks so that the code can
easily be tested with the type checks and then built
with the strong type checks disabled so the resulting
code can be used.Require strong mandatory type checks when enabling the user namespace.
It is very simple to make a typo and use the wrong type allowing
conversions to/from userspace values to be bypassed by accident,
the strong type checks prevent this.Acked-by: Serge Hallyn
Signed-off-by: Eric W. Biederman -
Start distinguishing between internal kernel uids and gids and
values that userspace can use. This is done by introducing two
new types: kuid_t and kgid_t. These types and their associated
functions are infrastructure are declared in the new header
uidgid.h.Ultimately there will be a different implementation of the mapping
functions for use with user namespaces. But to keep it simple
we introduce the mapping functions first to separate the meat
from the mechanical code conversions.Export overflowuid and overflowgid so we can use from_kuid_munged
and from_kgid_munged in modular code.Acked-by: Serge Hallyn
Signed-off-by: Eric W. Biederman