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

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Date:	Mon, 7 Sep 2015 20:11:48 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Luis Henriques <luis.henriques@...onical.com>
Cc:	Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] zram: fix possible use after free in zcomp_create()

On (09/07/15 11:33), Luis Henriques wrote:
> 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.
> 

good catch.

we probably better start checking the zcomp_strm_multi_create()/
zcomp_strm_single_create() status in zcomp_create(); that's much
more obvious and that's why we return it in the first place.

what do you think?

---

 drivers/block/zram/zcomp.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index 3456d5a..16bbc8c 100644
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -360,6 +360,7 @@ struct zcomp *zcomp_create(const char *compress, int max_strm)
 {
 	struct zcomp *comp;
 	struct zcomp_backend *backend;
+	int ret;
 
 	backend = find_backend(compress);
 	if (!backend)
@@ -371,10 +372,10 @@ struct zcomp *zcomp_create(const char *compress, int max_strm)
 
 	comp->backend = backend;
 	if (max_strm > 1)
-		zcomp_strm_multi_create(comp, max_strm);
+		ret = zcomp_strm_multi_create(comp, max_strm);
 	else
-		zcomp_strm_single_create(comp);
-	if (!comp->stream) {
+		ret = zcomp_strm_single_create(comp);
+	if (ret != 0) {
 		kfree(comp);
 		return ERR_PTR(-ENOMEM);
 	}

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