From 14834c4f4eb3c8c0af40f6203dbf09d232044d9d Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 25 Oct 2021 09:48:23 -0700 Subject: [PATCH] ipv4: annotate data races arount inet->min_ttl No report yet from KCSAN, yet worth documenting the races. Signed-off-by: Eric Dumazet Acked-by: Soheil Hassas Yeganeh Signed-off-by: Jakub Kicinski --- net/ipv4/ip_sockglue.c | 5 ++++- net/ipv4/tcp_ipv4.c | 7 +++++-- 2 files changed, 9 insertions(+), 3 deletions(-) diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c index b297bb28556e..d5487c858067 100644 --- a/net/ipv4/ip_sockglue.c +++ b/net/ipv4/ip_sockglue.c @@ -1352,7 +1352,10 @@ static int do_ip_setsockopt(struct sock *sk, int level, int optname, goto e_inval; if (val < 0 || val > 255) goto e_inval; - inet->min_ttl = val; + /* tcp_v4_err() and tcp_v4_rcv() might read min_ttl + * while we are changint it. + */ + WRITE_ONCE(inet->min_ttl, val); break; default: diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 2bdc32c1afb6..a9cbc8e6b796 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -508,7 +508,8 @@ int tcp_v4_err(struct sk_buff *skb, u32 info) if (sk->sk_state == TCP_CLOSE) goto out; - if (unlikely(iph->ttl < inet_sk(sk)->min_ttl)) { + /* min_ttl can be changed concurrently from do_ip_setsockopt() */ + if (unlikely(iph->ttl < READ_ONCE(inet_sk(sk)->min_ttl))) { __NET_INC_STATS(net, LINUX_MIB_TCPMINTTLDROP); goto out; } @@ -2068,7 +2069,9 @@ int tcp_v4_rcv(struct sk_buff *skb) return 0; } } - if (unlikely(iph->ttl < inet_sk(sk)->min_ttl)) { + + /* min_ttl can be changed concurrently from do_ip_setsockopt() */ + if (unlikely(iph->ttl < READ_ONCE(inet_sk(sk)->min_ttl))) { __NET_INC_STATS(net, LINUX_MIB_TCPMINTTLDROP); goto discard_and_relse; }