sysctl: check length at deprecated_sysctl_warning

Original patch assumed args->nlen < CTL_MAXNAME, but it can be false.
Signed-off-by: NTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/sysctl.c

@@ -2620,6 +2620,10 @@ static int deprecated_sysctl_warning(struct __sysctl_args *args)
 	int name[CTL_MAXNAME];
 	int i;
 
+	/* Check args->nlen. */
+	if (args->nlen < 0 || args->nlen > CTL_MAXNAME)
+		return -ENOTDIR;
+
 	/* Read in the sysctl name for better debug message logging */
 	for (i = 0; i < args->nlen; i++)
 		if (get_user(name[i], args->name + i))