From 14dd92d0a1174d3fe052bf87a3ae3a6914946170 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 14 Nov 2023 17:23:40 +0000 Subject: [PATCH 1/2] tcp: use tp->total_rto to track number of linear timeouts in SYN_SENT state In commit ccce324dabfe ("tcp: make the first N SYN RTO backoffs linear") David used icsk->icsk_backoff field to track the number of linear timeouts. Since then, tp->total_rto has been added. This commit uses tp->total_rto instead of icsk->icsk_backoff so that tcp_ld_RTO_revert() no longer can trigger an overflow in inet_csk_rto_backoff(). Other than the potential UBSAN report, there was no issue because receiving an ICMP message currently aborts the connect(). In the following patch, we want to adhere to RFC 6069 and RFC 1122 4.2.3.9. Signed-off-by: Eric Dumazet Cc: David Morley Cc: Neal Cardwell Cc: Yuchung Cheng Signed-off-by: David S. Miller --- net/ipv4/tcp_timer.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index 1f9f6c1c196b..d1ad20ce1c8c 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -626,7 +626,6 @@ void tcp_retransmit_timer(struct sock *sk) * implemented ftp to mars will work nicely. We will have to fix * the 120 second clamps though! */ - icsk->icsk_backoff++; out_reset_timer: /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is @@ -647,11 +646,12 @@ void tcp_retransmit_timer(struct sock *sk) tcp_rto_min(sk), TCP_RTO_MAX); } else if (sk->sk_state != TCP_SYN_SENT || - icsk->icsk_backoff > + tp->total_rto > READ_ONCE(net->ipv4.sysctl_tcp_syn_linear_timeouts)) { /* Use normal (exponential) backoff unless linear timeouts are * activated. */ + icsk->icsk_backoff++; icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); } inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, From 0a8de364ff7a14558e9676f424283148110384d6 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 14 Nov 2023 17:23:41 +0000 Subject: [PATCH 2/2] tcp: no longer abort SYN_SENT when receiving some ICMP Currently, non fatal ICMP messages received on behalf of SYN_SENT sockets do call tcp_ld_RTO_revert() to implement RFC 6069, but immediately call tcp_done(), thus aborting the connect() attempt. This violates RFC 1122 following requirement: 4.2.3.9 ICMP Messages ... o Destination Unreachable -- codes 0, 1, 5 Since these Unreachable messages indicate soft error conditions, TCP MUST NOT abort the connection, and it SHOULD make the information available to the application. This patch makes sure non 'fatal' ICMP[v6] messages do not abort the connection attempt. It enables RFC 6069 for SYN_SENT sockets as a result. Signed-off-by: Eric Dumazet Cc: David Morley Cc: Neal Cardwell Cc: Yuchung Cheng Signed-off-by: David S. Miller --- net/ipv4/tcp_ipv4.c | 6 ++++++ net/ipv6/tcp_ipv6.c | 9 ++++++--- 2 files changed, 12 insertions(+), 3 deletions(-) diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 5f693bbd578d..86cc6d36f818 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -482,6 +482,7 @@ int tcp_v4_err(struct sk_buff *skb, u32 info) const int code = icmp_hdr(skb)->code; struct sock *sk; struct request_sock *fastopen; + bool harderr = false; u32 seq, snd_una; int err; struct net *net = dev_net(skb->dev); @@ -555,6 +556,7 @@ int tcp_v4_err(struct sk_buff *skb, u32 info) goto out; case ICMP_PARAMETERPROB: err = EPROTO; + harderr = true; break; case ICMP_DEST_UNREACH: if (code > NR_ICMP_UNREACH) @@ -579,6 +581,7 @@ int tcp_v4_err(struct sk_buff *skb, u32 info) } err = icmp_err_convert[code].errno; + harderr = icmp_err_convert[code].fatal; /* check if this ICMP message allows revert of backoff. * (see RFC 6069) */ @@ -604,6 +607,9 @@ int tcp_v4_err(struct sk_buff *skb, u32 info) ip_icmp_error(sk, skb, err, th->dest, info, (u8 *)th); + if (!harderr) + break; + if (!sock_owned_by_user(sk)) { WRITE_ONCE(sk->sk_err, err); diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c index 937a02c2e534..43deda49cc52 100644 --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -381,7 +381,7 @@ static int tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt, struct tcp_sock *tp; __u32 seq, snd_una; struct sock *sk; - bool fatal; + bool harderr; int err; sk = __inet6_lookup_established(net, net->ipv4.tcp_death_row.hashinfo, @@ -402,9 +402,9 @@ static int tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt, return 0; } seq = ntohl(th->seq); - fatal = icmpv6_err_convert(type, code, &err); + harderr = icmpv6_err_convert(type, code, &err); if (sk->sk_state == TCP_NEW_SYN_RECV) { - tcp_req_err(sk, seq, fatal); + tcp_req_err(sk, seq, harderr); return 0; } @@ -489,6 +489,9 @@ static int tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt, ipv6_icmp_error(sk, skb, err, th->dest, ntohl(info), (u8 *)th); + if (!harderr) + break; + if (!sock_owned_by_user(sk)) { WRITE_ONCE(sk->sk_err, err); sk_error_report(sk); /* Wake people up to see the error (see connect in sock.c) */