linux-kernel - [PATCH v2] 9p/cache.c: Fix memory leak in v9fs_cache_session_get

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Date:   Thu, 23 May 2019 01:15:19 +0530
From:   Bharath Vedartham <linux.bhar@...il.com>
To:     ericvh@...il.com, asmadeus@...ewreck.org, lucho@...kov.net
Cc:     linux-kernel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net,
        linux.bhar@...il.com
Subject: [PATCH v2] 9p/cache.c: Fix memory leak in
 v9fs_cache_session_get_cookie

v9fs_cache_session_get_cookie assigns a random cachetag to v9ses->cachetag,
if the cachetag is not assigned previously.

v9fs_random_cachetag allocates memory to v9ses->cachetag with kmalloc and uses
scnprintf to fill it up with a cachetag.

But if scnprintf fails, v9ses->cachetag is not freed in the current
code causing a memory leak.

Fix this by freeing v9ses->cachetag it v9fs_random_cachetag fails.

This was reported by syzbot, the link to the report is below:
https://syzkaller.appspot.com/bug?id=f012bdf297a7a4c860c38a88b44fbee43fd9bbf3

Reported-by: syzbot+3a030a73b6c1e9833815@...kaller.appspotmail.com
Signed-off-by: Bharath Vedartham <linux.bhar@...il.com>

---
Changes since v2
	- Made v9ses->cachetag NULL after freeing to avoid any
	  side effects.
---
 fs/9p/cache.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/9p/cache.c b/fs/9p/cache.c
index 9eb3470..baf72da 100644
--- a/fs/9p/cache.c
+++ b/fs/9p/cache.c
@@ -66,6 +66,8 @@ void v9fs_cache_session_get_cookie(struct v9fs_session_info *v9ses)
 	if (!v9ses->cachetag) {
 		if (v9fs_random_cachetag(v9ses) < 0) {
 			v9ses->fscache = NULL;
+			kfree(v9ses->cachetag);
+			v9ses->cachetag = NULL; 
 			return;
 		}
 	}
-- 
2.7.4