linux-kernel - [PATCH] memcg_write_event_control(): fix a user-triggerable oops

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Message-ID: <20240726054357.GD99483@ZenIV>
Date: Fri, 26 Jul 2024 06:43:57 +0100
From: Al Viro <viro@...iv.linux.org.uk>
To: cgroups@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] memcg_write_event_control(): fix a user-triggerable oops

We are *not* guaranteed that anything past the terminating NUL
is mapped (let alone initialized with anything sane).
    
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
index 2aeea4d8bf8e..417c96f2da28 100644
--- a/mm/memcontrol-v1.c
+++ b/mm/memcontrol-v1.c
@@ -1842,9 +1842,12 @@ 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)