From 41c87425a1ac9b633e0fcc78eb1f19640c8fb5a0 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Mon, 9 Oct 2017 14:14:51 +0200 Subject: netlink: do not set cb_running if dump's start() errs It turns out that multiple places can call netlink_dump(), which means it's still possible to dereference partially initialized values in dump() that were the result of a faulty returned start(). This fixes the issue by calling start() _before_ setting cb_running to true, so that there's no chance at all of hitting the dump() function through any indirect paths. It also moves the call to start() to be when the mutex is held. This has the nice side effect of serializing invocations to start(), which is likely desirable anyway. It also prevents any possible other races that might come out of this logic. In testing this with several different pieces of tricky code to trigger these issues, this commit fixes all avenues that I'm aware of. Signed-off-by: Jason A. Donenfeld Cc: Johannes Berg Reviewed-by: Johannes Berg Signed-off-by: David S. Miller --- net/netlink/af_netlink.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) (limited to 'net/netlink') diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 94c11cf0459d..f34750691c5c 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -2266,16 +2266,17 @@ int __netlink_dump_start(struct sock *ssk, struct sk_buff *skb, cb->min_dump_alloc = control->min_dump_alloc; cb->skb = skb; + if (cb->start) { + ret = cb->start(cb); + if (ret) + goto error_unlock; + } + nlk->cb_running = true; mutex_unlock(nlk->cb_mutex); - ret = 0; - if (cb->start) - ret = cb->start(cb); - - if (!ret) - ret = netlink_dump(sk); + ret = netlink_dump(sk); sock_put(sk); -- cgit v1.2.3-59-g8ed1b