9p/cache.c: Fix memory leak in v9fs_cache_session_get_cookie

commit 962a991c5de18452d6c429d99f3039387cf5cbb0 upstream.

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

Link: http://lkml.kernel.org/r/20190522194519.GA5313@bharath12345-Inspiron-5559
Reported-by: syzbot+3a030a73b6c1e9833815@syzkaller.appspotmail.com
Signed-off-by: Bharath Vedartham <linux.bhar@gmail.com>
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/9p/cache.c b/fs/9p/cache.c
index 9eb34701a566c84cd05b4923427c5ca3f73ba12c..a43a8d2436db5de30bf9d852256a4806e894bee2 100644 (file)
--- 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;
                }
        }