linux-kernel - [ 37/73] udf: Improve table length check to avoid possible overflow

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Date:	Tue, 31 Jul 2012 05:43:47 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Jan Kara <jack@...e.cz>
Subject: [ 37/73] udf: Improve table length check to avoid possible overflow

3.2-stable review patch.  If anyone has any objections, please let me know.

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

From: Jan Kara <jack@...e.cz>

commit 57b9655d01ef057a523e810d29c37ac09b80eead upstream.

When a partition table length is corrupted to be close to 1 << 32, the
check for its length may overflow on 32-bit systems and we will think
the length is valid. Later on the kernel can crash trying to read beyond
end of buffer. Fix the check to avoid possible overflow.

Reported-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/udf/super.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/udf/super.c b/fs/udf/super.c
index 8a75838..dcbf987 100644
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -1340,7 +1340,7 @@ static int udf_load_logicalvol(struct super_block *sb, sector_t block,
 	BUG_ON(ident != TAG_IDENT_LVD);
 	lvd = (struct logicalVolDesc *)bh->b_data;
 	table_len = le32_to_cpu(lvd->mapTableLength);
-	if (sizeof(*lvd) + table_len > sb->s_blocksize) {
+	if (table_len > sb->s_blocksize - sizeof(*lvd)) {
 		udf_err(sb, "error loading logical volume descriptor: "
 			"Partition table too long (%u > %lu)\n", table_len,
 			sb->s_blocksize - sizeof(*lvd));


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