linux-kernel - [slabinfo PATCH v2] Fix off-by-one buffer corruption after readlink() call

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Date:	Mon, 17 Oct 2011 16:48:10 +0200
From:	Thomas Jarosch <thomas.jarosch@...ra2net.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	David Rientjes <rientjes@...gle.com>,
	Christoph Lameter <cl@...two.org>, linux-kernel@...r.kernel.org
Subject: [slabinfo PATCH v2] Fix off-by-one buffer corruption after readlink() call

readlink() never zero terminates the provided buffer.
Therefore we already do

    buffer[count] = 0;

This leads to an off-by-one buffer corruption as readlink()
might return the full size of the buffer.

The common technique is to reduce the buffer size by one.
Another fix would be to check

"
if (count < 0 || count == sizeof(buffer))
    fatal();
"

Reducing the buffer size by one is easier IMHO.

Signed-off-by: Thomas Jarosch <thomas.jarosch@...ra2net.com>
Acked-by: David Rientjes <rientjes@...gle.com>
Acked-by: Christoph Lameter <cl@...two.org>
---
 tools/slub/slabinfo.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/tools/slub/slabinfo.c b/tools/slub/slabinfo.c
index 868cc93..cc1a378 100644
--- a/tools/slub/slabinfo.c
+++ b/tools/slub/slabinfo.c
@@ -1145,7 +1145,7 @@ static void read_slab_dir(void)
 		switch (de->d_type) {
 		   case DT_LNK:
 			alias->name = strdup(de->d_name);
-			count = readlink(de->d_name, buffer, sizeof(buffer));
+			count = readlink(de->d_name, buffer, sizeof(buffer)-1);
 
 			if (count < 0)
 				fatal("Cannot read symlink %s\n", de->d_name);
-- 
1.7.6.4
--
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