zram: fix possible use after free in zcomp_create()

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")
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index 965d1af..5cb13ca 100644 (file)
--- 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;
 }