[PATCH v2] ucounts: fix counter leak in inc_rlimit_get_ucounts()

[PATCH v2] ucounts: fix counter leak in inc_rlimit_get_ucounts()

[Roman Gushchin]

From: Andrei Vagin <avagin@google.com>

The inc_rlimit_get_ucounts() increments the specified rlimit counter and
then checks its limit. If the value exceeds the limit, the function
returns an error without decrementing the counter.

v2: changed the goto label name [Roman]

Fixes: 15bc01effefe ("ucounts: Fix signal ucount refcounting")
Signed-off-by: Andrei Vagin <avagin@google.com>
Co-developed-by: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Tested-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Alexey Gladkov <legion@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Andrei Vagin <avagin@google.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Alexey Gladkov <legion@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: <stable@vger.kernel.org>
---
 kernel/ucount.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/ucount.c b/kernel/ucount.c
index 8c07714ff27d..9469102c5ac0 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -317,7 +317,7 @@ long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type)
 	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
 		long new = atomic_long_add_return(1, &iter->rlimit[type]);
 		if (new < 0 || new > max)
-			goto unwind;
+			goto dec_unwind;
 		if (iter == ucounts)
 			ret = new;
 		max = get_userns_rlimit_max(iter->ns, type);
@@ -334,7 +334,6 @@ long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type)
 dec_unwind:
 	dec = atomic_long_sub_return(1, &iter->rlimit[type]);
 	WARN_ON_ONCE(dec < 0);
-unwind:
 	do_dec_rlimit_put_ucounts(ucounts, iter, type);
 	return 0;
 }
-- 
2.47.0.163.g1226f6d8fa-goog

Re: [PATCH v2] ucounts: fix counter leak in inc_rlimit_get_ucounts()

[Andrew Morton]

On Fri,  1 Nov 2024 19:19:40 +0000 Roman Gushchin <roman.gushchin@linux.dev> wrote:

> The inc_rlimit_get_ucounts() increments the specified rlimit counter and
> then checks its limit. If the value exceeds the limit, the function
> returns an error without decrementing the counter.

Please (always) provide a description of the userspace visible effects
of the flaw.

> Cc: <stable@vger.kernel.org>

Especially when proposing this!