linux-kernel - [PATCH v4] scatterlist: prevent invalid free when alloc fails

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Message-Id: <20100830160556.7F840603843@il93ubuntu.localdomain>
Date:	Mon, 30 Aug 2010 11:04:15 -0500
From:	Jeffrey Carlyle <jeff.carlyle@...orola.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	OLUSANYA SOYANNWO <olusanya.soyannwo@...orola.com>,
	<linux-kernel@...r.kernel.org>, Hu Tao <taohu@...orola.com>,
	<jaxboe@...ionio.com>, <torvalds@...l.org>,
	Jeffrey Carlyle <jeff.carlyle@...orola.com>
Subject: [PATCH v4] scatterlist: prevent invalid free when alloc fails

When alloc fails, free_table is being called. Depending on the number of
bytes requested, we determine if we are going to call _get_free_page()
or kmalloc(). When alloc fails, our math is wrong (due to sg_size - 1),
and the last buffer is wrongfully assumed to have been allocated by
kmalloc. Hence, kfree gets called and a panic occurs.

Signed-off-by: Jeffrey Carlyle <jeff.carlyle@...orola.com>
Signed-off-by: Olusanya Soyannwo <c23746@...orola.com>
Cc: Tejun Heo <tj@...nel.org>
Cc: Jens Axboe <jaxboe@...ionio.com>
---
 lib/scatterlist.c |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index a5ec428..a654897 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -248,8 +248,18 @@ int __sg_alloc_table(struct sg_table *table, unsigned int nents,
 		left -= sg_size;
 
 		sg = alloc_fn(alloc_size, gfp_mask);
-		if (unlikely(!sg))
+		if (unlikely(!sg)) {
+			/*
+			 * Adjust entry count to reflect that the last
+			 * entry of the previous table won't be used for
+			 * linkage.  Without this, sg_kfree() may get
+			 * confused.
+			 */
+			if(pvr)
+				table->nents = ++table->orig_nents;
+
 			return -ENOMEM;
+		}
 
 		sg_init_table(sg, alloc_size);
 		table->nents = table->orig_nents += sg_size;
-- 
1.6.3.3

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