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Subject[GIT PULL] ucount fixes for v5.15

Linus,

Please pull the ucount-fixes-for-v5.15 branch from the git tree:

git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git ucount-fixes-for-v5.15

HEAD: 5ebcbe342b1c12fae44b4f83cbeae1520e09857e ucounts: Move get_ucounts from cred_alloc_blank to key_change_session_keyring

There has been one very hard to track down bug in the ucount code that
we have been tracking since roughly v5.14 was released. Alex managed to
find a reliable reproducer a few days ago and then I was able to
instrument the code and figure out what the issue was.

It turns out the sigqueue_alloc single atomic operation optimization did
not play nicely with ucounts multiple level rlimits. It turned out that
either sigqueue_alloc or sigqueue_free could be operating on multiple
levels and trigger the conditions for the optimization on more than one
level at the same time.

To deal with that situation I have introduced inc_rlimit_get_ucounts
and dec_rlimit_put_ucounts that just focuses on the optimization and
the rlimit and ucount changes.

While looking into the big bug I found I couple of other little issues
so I am including those fixes here as well.


When I have time I would very much like to dig into process ownership of
the shared signal queue and see if we could pick a single owner for the
entire queue so that all of the rlimits can count to that owner. Which
should entirely remove the need to call get_ucounts and put_ucounts
in sigqueue_alloc and sigqueue_free. It is difficult because Linux
unlike POSIX supports setuid that works on a single thread.

Eric W. Biederman (4):
ucounts: Fix signal ucount refcounting
ucounts: Pair inc_rlimit_ucounts with dec_rlimit_ucoutns in commit_creds
ucounts: Proper error handling in set_cred_ucounts
ucounts: Move get_ucounts from cred_alloc_blank to key_change_session_keyring

kernel/cred.c | 9 ++++-----
security/keys/process_keys.c | 8 ++++++++
2 files changed, 12 insertions(+), 5 deletions(-)

Eric

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