linux-kernel - [PATCH 1/1] swapfile: swap_info_get: Check for swap

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Date:	Mon, 26 Dec 2011 17:26:39 +0530
From:	Kautuk Consul <consul.kautuk@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Cesar Eduardo Barros <cesarb@...arb.net>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Eric B Munson <emunson@...bm.net>,
	Pekka Enberg <penberg@...nel.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Kautuk Consul <consul.kautuk@...il.com>
Subject: [PATCH 1/1] swapfile: swap_info_get: Check for swap_info[type] == NULL

From: Kautuk Consul <consul.kautuk@...il.com>

If the swapfile type encoded within entry.val is corrupted in
such a way that the swap_info[type] == NULL, then the code in
swap_info_get will cause a NULL pointer exception.

Assuming that the code in swap_info_get attempts to validate the
swapfile type by checking its range, another bad_nofile check would
be to check for check whether the swap_info[type] pointer is NULL.

Adding a NULL check for swap_info[type] to be reagrded as a "bad_nofile"
error scenario.

Signed-off-by: Kautuk Consul <consul.kautuk@...il.com>
---
 mm/swapfile.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index b1cd120..7bdbe91 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -483,6 +483,8 @@ static struct swap_info_struct *swap_info_get(swp_entry_t entry)
 	if (type >= nr_swapfiles)
 		goto bad_nofile;
 	p = swap_info[type];
+	if (!p)
+		goto bad_nofile;
 	if (!(p->flags & SWP_USED))
 		goto bad_device;
 	offset = swp_offset(entry);
-- 
1.7.6

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