From 0af0e1dba97dc53b9f14795ca49b0b1b24aa0ce1 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Wed, 8 Oct 2014 23:44:00 -0400 Subject: fix misuses of f_count() in ppp and netlink commit 24dff96a37a2ca319e75a74d3929b2de22447ca6 upstream. we used to check for "nobody else could start doing anything with that opened file" by checking that refcount was 2 or less - one for descriptor table and one we'd acquired in fget() on the way to wherever we are. That was race-prone (somebody else might have had a reference to descriptor table and do fget() just as we'd been checking) and it had become flat-out incorrect back when we switched to fget_light() on those codepaths - unlike fget(), it doesn't grab an extra reference unless the descriptor table is shared. The same change allowed a race-free check, though - we are safe exactly when refcount is less than 2. It was a long time ago; pre-2.6.12 for ioctl() (the codepath leading to ppp one) and 2.6.17 for sendmsg() (netlink one). OTOH, netlink hadn't grown that check until 3.9 and ppp used to live in drivers/net, not drivers/net/ppp until 3.1. The bug existed well before that, though, and the same fix used to apply in old location of file. Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman --- net/netlink/af_netlink.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net/netlink') diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 5ed562dfe74..afe41178c9f 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -571,7 +571,7 @@ static int netlink_mmap_sendmsg(struct sock *sk, struct msghdr *msg, * after validation, the socket and the ring may only be used by a * single process, otherwise we fall back to copying. */ - if (atomic_long_read(&sk->sk_socket->file->f_count) > 2 || + if (atomic_long_read(&sk->sk_socket->file->f_count) > 1 || atomic_read(&nlk->mapped) > 1) excl = false; -- cgit v1.2.3