[PATCH 3.16.y-ckt 020/104] zram: fix possible use after free in zcomp_create()

[Luis Henriques]

3.16.7-ckt19 -stable review patch.  If anyone has any objections, please let me know.

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

From: Luis Henriques <luis.henriques at canonical.com>

commit 3aaf14da807a4e9931a37f21e4251abb8a67021b upstream.

zcomp_create() verifies the success of zcomp_strm_{multi,single}_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")
Acked-by: Sergey Senozhatsky <sergey.senozhatsky at gmail.com>
Acked-by: Minchan Kim <minchan at kernel.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 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 f1ff39a3d1c1..54d946a9eee6 100644
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -325,12 +325,14 @@ 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)
@@ -342,12 +344,12 @@ 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;
 }