Re: [held lock freed] Re: [GIT] Networking

On Monday 21 March 2011, Eric Dumazet wrote:

quoted

diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
index 4680b1e..b2cf1db 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c

@@ -669,8 +669,8 @@ static int x25_release(struct socket *sock)
 
      sock_orphan(sk);
 out:
-     release_sock(sk);
      sock_put(sk);
+     release_sock(sk);
      return 0;
 }
 

Hmm, x25_release() looks fine, I believe no fix is needed.

D'oh. You're right of course. My patch would introduce the bug,
not fix it. Updated patch below.

	Arnd
8<-------------------------
net/appletalk: fix atalk_release use after free

The BKL removal in appletalk introduced a use-after-free problem,
where atalk_destroy_socket frees a sock, but we still release
the socket lock on it.

An easy fix is to take an extra reference on the sock and sock_put
it when returning from atalk_release.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

index 3d4f4b0..206e771 100644

--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c

@@ -1051,6 +1051,7 @@ static int atalk_release(struct socket *sock)
 {
 	struct sock *sk = sock->sk;
 
+	sock_hold(sk);
 	lock_sock(sk);
 	if (sk) {
 		sock_orphan(sk);

@@ -1058,6 +1059,8 @@ static int atalk_release(struct socket *sock)
 		atalk_destroy_socket(sk);
 	}
 	release_sock(sk);
+	sock_put(sk);
+
 	return 0;
 }