From: Al Viro <viro@zeniv.linux.org.uk>
Date: Sun, 21 Jul 2024 18:45:08 +0000 (-0400)
Subject: memcg_write_event_control(): fix a user-triggerable oops
X-Git-Tag: v6.10.7~205
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=21b578f1d599edb87462f11113c5b0fc7a04ac61;p=thirdparty%2Fkernel%2Fstable.git

memcg_write_event_control(): fix a user-triggerable oops

commit 046667c4d3196938e992fba0dfcde570aa85cd0e upstream.

we are *not* guaranteed that anything past the terminating NUL
is mapped (let alone initialized with anything sane).

Fixes: 0dea116876ee ("cgroup: implement eventfd-based generic API for notifications")
Cc: stable@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 88c7a0861017c..332f190bf3d6b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5282,9 +5282,12 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
 	buf = endp + 1;
 
 	cfd = simple_strtoul(buf, &endp, 10);
-	if ((*endp != ' ') && (*endp != '\0'))
+	if (*endp == '\0')
+		buf = endp;
+	else if (*endp == ' ')
+		buf = endp + 1;
+	else
 		return -EINVAL;
-	buf = endp + 1;
 
 	event = kzalloc(sizeof(*event), GFP_KERNEL);
 	if (!event)