The patch titled Subject: signal: restore the override_rlimit logic has been added to the -mm mm-hotfixes-unstable branch. Its filename is signal-restore-the-override_rlimit-logic.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Roman Gushchin roman.gushchin@linux.dev Subject: signal: restore the override_rlimit logic Date: Mon, 4 Nov 2024 19:54:19 +0000

Prior to commit d64696905554 ("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: d64696905554 ("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 Cc: Kees Cook kees@kernel.org Cc: "Eric W. Biederman" ebiederm@xmission.com Cc: Alexey Gladkov legion@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

include/linux/user_namespace.h | 3 ++- kernel/signal.c | 3 ++- kernel/ucount.c | 6 ++++-- 3 files changed, 8 insertions(+), 4 deletions(-)

--- a/include/linux/user_namespace.h~signal-restore-the-override_rlimit-logic +++ a/include/linux/user_namespace.h @@ -141,7 +141,8 @@ static inline long get_rlimit_value(stru

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);

--- a/kernel/signal.c~signal-restore-the-override_rlimit-logic +++ a/kernel/signal.c @@ -419,7 +419,8 @@ __sigqueue_alloc(int sig, struct task_st */ 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; --- a/kernel/ucount.c~signal-restore-the-override_rlimit-logic +++ a/kernel/ucount.c @@ -307,7 +307,8 @@ void dec_rlimit_put_ucounts(struct ucoun 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; @@ -320,7 +321,8 @@ long inc_rlimit_get_ucounts(struct ucoun goto dec_unwind; if (iter == ucounts) ret = new; - max = get_userns_rlimit_max(iter->ns, type); + if (!override_rlimit) + max = get_userns_rlimit_max(iter->ns, type); /* * Grab an extra ucount reference for the caller when * the rlimit count was previously 0. _

Patches currently in -mm which might be from roman.gushchin@linux.dev are

signal-restore-the-override_rlimit-logic.patch