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signal: restore the override_rlimit logic

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Prior to commit d646969055 ("Reimplement RLIMIT_SIGPENDING on top of
ucounts") UCOUNT_RLIMIT_SIGPENDING rlimit was not enforced for a class of
signals.  However now it's enforced unconditionally, even if
override_rlimit is set.  This behavior change caused production issues.  

For example, if the limit is reached and a process receives a SIGSEGV
signal, sigqueue_alloc fails to allocate the necessary resources for the
signal delivery, preventing the signal from being delivered with siginfo. 
This prevents the process from correctly identifying the fault address and
handling the error.  From the user-space perspective, applications are
unaware that the limit has been reached and that the siginfo is
effectively 'corrupted'.  This can lead to unpredictable behavior and
crashes, as we observed with java applications.

Fix this by passing override_rlimit into inc_rlimit_get_ucounts() and skip
the comparison to max there if override_rlimit is set.  This effectively
restores the old behavior.

Link: https://lkml.kernel.org/r/20241104195419.3962584-1-roman.gushchin@linux.dev
Fixes: d646969055 ("Reimplement RLIMIT_SIGPENDING on top of ucounts")
Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Co-developed-by: Andrei Vagin <avagin@google.com>
Signed-off-by: Andrei Vagin <avagin@google.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Alexey Gladkov <legion@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Roman Gushchin 2024-11-04 19:54:19 +00:00 committed by Andrew Morton
parent b8ee299855
commit 9e05e5c7ee
3 changed files with 8 additions and 4 deletions
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3
include/linux/user_namespace.h
View File

@ -141,7 +141,8 @@ static inline long get_rlimit_value(struct ucounts *ucounts, enum rlimit_type ty
long inc_rlimit_ucounts(struct ucounts *ucounts, enum rlimit_type type, long v);
bool dec_rlimit_ucounts(struct ucounts *ucounts, enum rlimit_type type, long v);
long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type);
long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type,
bool override_rlimit);
void dec_rlimit_put_ucounts(struct ucounts *ucounts, enum rlimit_type type);
bool is_rlimit_overlimit(struct ucounts *ucounts, enum rlimit_type type, unsigned long max);

3
kernel/signal.c
View File

@ -419,7 +419,8 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t gfp_flags,
*/
rcu_read_lock();
ucounts = task_ucounts(t);
sigpending = inc_rlimit_get_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING);
sigpending = inc_rlimit_get_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING,
override_rlimit);
rcu_read_unlock();
if (!sigpending)
return NULL;

4
kernel/ucount.c
View File

@ -307,7 +307,8 @@ void dec_rlimit_put_ucounts(struct ucounts *ucounts, enum rlimit_type type)
do_dec_rlimit_put_ucounts(ucounts, NULL, type);
}
long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type)
long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type,
bool override_rlimit)
{
/* Caller must hold a reference to ucounts */
struct ucounts *iter;
@ -320,6 +321,7 @@ long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type)
goto dec_unwind;
if (iter == ucounts)
ret = new;
if (!override_rlimit)
max = get_userns_rlimit_max(iter->ns, type);
/*
* Grab an extra ucount reference for the caller when