From: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
commit 8f2f9c4d82f24f172ae439e5035fc1e0e4c229dd upstream.
Michal Koutný <mkoutny@xxxxxxxx> wrote:
> It was reported that v5.14 behaves differently when enforcing
> RLIMIT_NPROC limit, namely, it allows one more task than previously.
> This is consequence of the commit 21d1c5e386bc ("Reimplement
> RLIMIT_NPROC on top of ucounts") that missed the sharpness of
> equality in the forking path.
This can be fixed either by fixing the test or by moving the increment
to be before the test. Fix it my moving copy_creds which contains
the increment before is_ucounts_overlimit.
In the case of CLONE_NEWUSER the ucounts in the task_cred changes.
The function is_ucounts_overlimit needs to use the final version of
the ucounts for the new process. Which means moving the
is_ucounts_overlimit test after copy_creds is necessary.
Both the test in fork and the test in set_user were semantically
changed when the code moved to ucounts. The change of the test in
fork was bad because it was before the increment. The test in
set_user was wrong and the change to ucounts fixed it. So this
fix only restores the old behavior in one lcation not two.
Link: https://lkml.kernel.org/r/20220204181144.24462-1-mkoutny@xxxxxxxx
Link: https://lkml.kernel.org/r/20220216155832.680775-2-ebiederm@xxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Michal Koutný <mkoutny@xxxxxxxx>
Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx>
Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts")
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/fork.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2055,18 +2055,18 @@ static __latent_entropy struct task_stru
#ifdef CONFIG_PROVE_LOCKING
DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
#endif
+ retval = copy_creds(p, clone_flags);
+ if (retval < 0)
+ goto bad_fork_free;
+
retval = -EAGAIN;
if (is_ucounts_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) {
if (p->real_cred->user != INIT_USER &&
!capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
- goto bad_fork_free;
+ goto bad_fork_cleanup_count;
}
current->flags &= ~PF_NPROC_EXCEEDED;
- retval = copy_creds(p, clone_flags);
- if (retval < 0)
- goto bad_fork_free;
-
/*
* If multiple threads are within copy_process(), then this check
* triggers too late. This doesn't hurt, the check is only there
