linux-kernel - [PATCH v3] zram: fix possible use after free in zcomp

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Date:	Tue,  8 Sep 2015 10:39:28 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH v3] zram: fix possible use after free in zcomp_create()

zcomp_create() verifies the success of zcomp_strm_{multi,siggle}_create()
through comp->stream, which can potentially be pointing to memory that was
freed if these functions returned an error.

While at it, replace a 'ERR_PTR(-ENOMEM)' by a more generic
'ERR_PTR(error)' as in the future zcomp_strm_{multi,siggle}_create() could
return other error codes.  Function documentation updated accordingly.

Fixes: beca3ec71fe5 ("zram: add multi stream functionality")
Cc: stable@...r.kernel.org
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc: Minchan Kim <minchan@...nel.org>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---

Changes since v2:
 * Renamed local variable 'ret' to 'error'
 * Usage of 'ERR_PTR(error)' to accommodate future error codes returned by
   zcomp_strm_{multi,siggle}_create
 (all suggested by Minchan)

Changes since v1:
 * Check zcomp_strm_{multi,siggle}_create() return code instead
   comp->stream (suggested by Sergey)

drivers/block/zram/zcomp.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index 965d1afb0eaa..5cb13ca3a3ac 100644
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -330,12 +330,14 @@ void zcomp_destroy(struct zcomp *comp)
  * allocate new zcomp and initialize it. return compressing
  * backend pointer or ERR_PTR if things went bad. ERR_PTR(-EINVAL)
  * if requested algorithm is not supported, ERR_PTR(-ENOMEM) in
- * case of allocation error.
+ * case of allocation error, or any other error potentially
+ * returned by functions zcomp_strm_{multi,single}_create.
  */
 struct zcomp *zcomp_create(const char *compress, int max_strm)
 {
 	struct zcomp *comp;
 	struct zcomp_backend *backend;
+	int error;
 
 	backend = find_backend(compress);
 	if (!backend)
@@ -347,12 +349,12 @@ struct zcomp *zcomp_create(const char *compress, int max_strm)
 
 	comp->backend = backend;
 	if (max_strm > 1)
-		zcomp_strm_multi_create(comp, max_strm);
+		error = zcomp_strm_multi_create(comp, max_strm);
 	else
-		zcomp_strm_single_create(comp);
-	if (!comp->stream) {
+		error = zcomp_strm_single_create(comp);
+	if (error) {
 		kfree(comp);
-		return ERR_PTR(-ENOMEM);
+		return ERR_PTR(error);
 	}
 	return comp;
 }
--
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