linux-kernel - [PATCH 3.2 83/87] uml: check length in exitcode_proc

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Message-ID: <lsq.1385387069.351537312@decadent.org.uk>
Date:	Mon, 25 Nov 2013 13:44:29 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Fabian Yamaguchi" <fabs@...sec.de>,
	"Dan Carpenter" <dan.carpenter@...cle.com>,
	"Nico Golde" <nico@...lde.de>
Subject: [PATCH 3.2 83/87] uml: check length in exitcode_proc_write()

3.2.53-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Carpenter <dan.carpenter@...cle.com>

commit 201f99f170df14ba52ea4c52847779042b7a623b upstream.

We don't cap the size of buffer from the user so we could write past the
end of the array here.  Only root can write to this file.

Reported-by: Nico Golde <nico@...lde.de>
Reported-by: Fabian Yamaguchi <fabs@...sec.de>
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/um/kernel/exitcode.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/um/kernel/exitcode.c
+++ b/arch/um/kernel/exitcode.c
@@ -40,9 +40,11 @@ static ssize_t exitcode_proc_write(struc
 		const char __user *buffer, size_t count, loff_t *pos)
 {
 	char *end, buf[sizeof("nnnnn\0")];
+	size_t size;
 	int tmp;
 
-	if (copy_from_user(buf, buffer, count))
+	size = min(count, sizeof(buf));
+	if (copy_from_user(buf, buffer, size))
 		return -EFAULT;
 
 	tmp = simple_strtol(buf, &end, 0);

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