[PATCH] afs: Fix afs_cb_interest refcnt leak in afs_select_fileserver()

[PATCH] afs: Fix afs_cb_interest refcnt leak in afs_select_fileserver()

[Xiyu Yang]

afs_select_fileserver() invokes afs_get_cb_interest(), which returns a
reference of the specified afs_cb_interest object to "fc->cbi" with
increased refcnt.

The reference counting issue happens in one exception handling path of
afs_select_fileserver(). When error occurred in
afs_wait_for_fs_probes(), the function forgets to decrease the refcnt
increased by afs_get_cb_interest(), causing a refcnt leak.

Fix this issue by calling afs_put_cb_interest() when error occurred in
afs_wait_for_fs_probes().

Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
---
 fs/afs/rotate.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/afs/rotate.c b/fs/afs/rotate.c
index 2a3305e42b14..f73af16cdb92 100644
--- a/fs/afs/rotate.c
+++ b/fs/afs/rotate.c
@@ -357,8 +357,10 @@ bool afs_select_fileserver(struct afs_fs_cursor *fc)
 	_debug("pick [%lx]", fc->untried);
 
 	error = afs_wait_for_fs_probes(fc->server_list, fc->untried);
-	if (error < 0)
+	if (error < 0) {
+		afs_put_cb_interest(afs_v2net(vnode), fc->cbi);
 		goto failed_set_error;
+	}
 
 	/* Pick the untried server with the lowest RTT.  If we have outstanding
 	 * callbacks, we stick with the server we're already using if we can.
-- 
2.7.4

Re: [PATCH] afs: Fix afs_cb_interest refcnt leak in afs_select_fileserver()

[David Howells]

Xiyu Yang <xiyuyang19@fudan.edu.cn> wrote:

>  	error = afs_wait_for_fs_probes(fc->server_list, fc->untried);
> -	if (error < 0)
> +	if (error < 0) {
> +		afs_put_cb_interest(afs_v2net(vnode), fc->cbi);
>  		goto failed_set_error;
> +	}

Ummm...  Did you try this?  afs_end_vnode_operation() should then cause a
double free because you don't clear fc->cbi.

You can try it by installing the kafs-client package if your distribution has
it available and starting the afs.mount service or doing:

	mount -t afs none /afs -o dyn

and then:

	ls /afs/grand.central.org/

David