From 58ad436fcf49810aa006016107f494c9ac9013db Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Tue, 13 Aug 2013 09:04:05 +0200 Subject: [PATCH] genetlink: fix family dump race When dumping generic netlink families, only the first dump call is locked with genl_lock(), which protects the list of families, and thus subsequent calls can access the data without locking, racing against family addition/removal. This can cause a crash. Fix it - the locking needs to be conditional because the first time around it's already locked. A similar bug was reported to me on an old kernel (3.4.47) but the exact scenario that happened there is no longer possible, on those kernels the first round wasn't locked either. Looking at the current code I found the race described above, which had also existed on the old kernel. Cc: stable@vger.kernel.org Reported-by: Andrei Otcheretianski Signed-off-by: Johannes Berg Signed-off-by: David S. Miller --- net/netlink/genetlink.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c index 512718adb0d5..f85f8a2ad6cf 100644 --- a/net/netlink/genetlink.c +++ b/net/netlink/genetlink.c @@ -789,6 +789,10 @@ static int ctrl_dumpfamily(struct sk_buff *skb, struct netlink_callback *cb) struct net *net = sock_net(skb->sk); int chains_to_skip = cb->args[0]; int fams_to_skip = cb->args[1]; + bool need_locking = chains_to_skip || fams_to_skip; + + if (need_locking) + genl_lock(); for (i = chains_to_skip; i < GENL_FAM_TAB_SIZE; i++) { n = 0; @@ -810,6 +814,9 @@ errout: cb->args[0] = i; cb->args[1] = n; + if (need_locking) + genl_unlock(); + return skb->len; } -- 2.20.1