linux-kernel - [PATCH] ucounts: Fix UCOUNT_RLIMIT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri,  2 Jul 2021 19:54:42 +0200
From:   Alexey Gladkov <legion@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux.dev>,
        Alexey Gladkov <legion@...nel.org>
Subject: [PATCH] ucounts: Fix UCOUNT_RLIMIT_SIGPENDING counter leak

If get_ucounts() could not increase the reference counter, then in case
of an error it will be impossible to decrease the counter.

In case of an error, the ucounts variable cannot be set to NULL. Also
dec_rlimit_ucounts() has to be REGARDLESS of whether get_ucounts() was
successful or not.

Signed-off-by: Alexey Gladkov <legion@...nel.org>
---
 kernel/signal.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index de0920353d30..87a64b3307a8 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -412,7 +412,7 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t gfp_flags,
 		 int override_rlimit, const unsigned int sigqueue_flags)
 {
 	struct sigqueue *q = NULL;
-	struct ucounts *ucounts = NULL;
+	struct ucounts *ucounts, *ucounts_new;
 	long sigpending;
 
 	/*
@@ -424,10 +424,10 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t gfp_flags,
 	 * changes from/to zero.
 	 */
 	rcu_read_lock();
-	ucounts = task_ucounts(t);
+	ucounts = ucounts_new = task_ucounts(t);
 	sigpending = inc_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING, 1);
 	if (sigpending == 1)
-		ucounts = get_ucounts(ucounts);
+		ucounts_new = get_ucounts(ucounts);
 	rcu_read_unlock();
 
 	if (override_rlimit || (sigpending < LONG_MAX && sigpending <= task_rlimit(t, RLIMIT_SIGPENDING))) {
@@ -437,13 +437,24 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t gfp_flags,
 	}
 
 	if (unlikely(q == NULL)) {
-		if (ucounts && dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING, 1))
-			put_ucounts(ucounts);
+		ucounts_new = NULL;
 	} else {
 		INIT_LIST_HEAD(&q->list);
 		q->flags = sigqueue_flags;
-		q->ucounts = ucounts;
+		q->ucounts = ucounts_new;
 	}
+
+	/*
+	 * In case it failed to allocate sigqueue or ucounts reference counter
+	 * overflow, we decrement UCOUNT_RLIMIT_SIGPENDING to avoid counter
+	 * leaks.
+	 */
+	if (unlikely(ucounts_new == NULL)) {
+		dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING, 1);
+		if (sigpending == 1)
+			put_ucounts(ucounts);
+	}
+
 	return q;
 }
 
@@ -451,7 +462,7 @@ static void __sigqueue_free(struct sigqueue *q)
 {
 	if (q->flags & SIGQUEUE_PREALLOC)
 		return;
-	if (q->ucounts && dec_rlimit_ucounts(q->ucounts, UCOUNT_RLIMIT_SIGPENDING, 1)) {
+	if (dec_rlimit_ucounts(q->ucounts, UCOUNT_RLIMIT_SIGPENDING, 1)) {
 		put_ucounts(q->ucounts);
 		q->ucounts = NULL;
 	}
-- 
2.29.3