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

From: Arnd Bergmann
Date: Mon Mar 21 2011 - 10:50:26 EST

On Monday 21 March 2011, Eric Dumazet wrote:
> [PATCH] ipx: fix ipx_release()
> Commit b0d0d915d1d1a0 (remove the BKL) added a regression, because
> sock_put() can free memory while we are going to use it later.
> Fix is to delay sock_put() after release_sock().
> Reported-by: Ingo Molnar <mingo@xxxxxxx>
> Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>

Your fix looks good, thanks Eric!

Acked-by: Arnd Bergmann <arnd@xxxxxxxx>

I believe I made the same mistake in atalk_release and x25_release:

net: fix atalk_release and x25_release

The recent BKL removal has introduced a use-after-free problem
in multiple network protocols. This fixes the problem in appletalk
and x25 by ensuring that we call the final sock_put() after
releasing the socket lock.

Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
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);
if (sk) {
@@ -1058,6 +1059,8 @@ static int atalk_release(struct socket *sock)
+ sock_put(sk);
return 0;

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)

- release_sock(sk);
+ release_sock(sk);
return 0;

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