From 48044eb490be71c203e14dd89e8bae87209eab52 Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Mon, 16 Oct 2017 17:09:53 +0200 Subject: [PATCH] netlink: fix netlink_ack() extack race It seems that it's possible to toggle NETLINK_F_EXT_ACK through setsockopt() while another thread/CPU is building a message inside netlink_ack(), which could then trigger the WARN_ON()s I added since if it goes from being turned off to being turned on between allocating and filling the message, the skb could end up being too small. Avoid this whole situation by storing the value of this flag in a separate variable and using that throughout the function instead. Fixes: 2d4bc93368f5 ("netlink: extended ACK reporting") Signed-off-by: Johannes Berg Signed-off-by: David S. Miller --- net/netlink/af_netlink.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index f34750691c5c..b93148e8e9fb 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -2307,6 +2307,7 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err, size_t tlvlen = 0; struct netlink_sock *nlk = nlk_sk(NETLINK_CB(in_skb).sk); unsigned int flags = 0; + bool nlk_has_extack = nlk->flags & NETLINK_F_EXT_ACK; /* Error messages get the original request appened, unless the user * requests to cap the error message, and get extra error data if @@ -2317,7 +2318,7 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err, payload += nlmsg_len(nlh); else flags |= NLM_F_CAPPED; - if (nlk->flags & NETLINK_F_EXT_ACK && extack) { + if (nlk_has_extack && extack) { if (extack->_msg) tlvlen += nla_total_size(strlen(extack->_msg) + 1); if (extack->bad_attr) @@ -2326,8 +2327,7 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err, } else { flags |= NLM_F_CAPPED; - if (nlk->flags & NETLINK_F_EXT_ACK && - extack && extack->cookie_len) + if (nlk_has_extack && extack && extack->cookie_len) tlvlen += nla_total_size(extack->cookie_len); } @@ -2355,7 +2355,7 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err, errmsg->error = err; memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) ? nlh->nlmsg_len : sizeof(*nlh)); - if (nlk->flags & NETLINK_F_EXT_ACK && extack) { + if (nlk_has_extack && extack) { if (err) { if (extack->_msg) WARN_ON(nla_put_string(skb, NLMSGERR_ATTR_MSG, -- 2.30.2