5.10-stable review patch. If anyone has any objections, please let me know.
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From: Wang Hai wanghai38@huawei.com
[ Upstream commit 8d52da23b6c68a0f6bad83959ebb61a2cf623c4e ]
Recently a bug was discovered where the server had entered TCP_ESTABLISHED state, but the upper layers were not notified.
The same 5-tuple packet may be processed by different CPUSs, so two CPUs may receive different ack packets at the same time when the state is TCP_NEW_SYN_RECV.
In that case, req->ts_recent in tcp_check_req may be changed concurrently, which will probably cause the newsk's ts_recent to be incorrectly large. So that tcp_validate_incoming will fail. At this point, newsk will not be able to enter the TCP_ESTABLISHED.
cpu1 cpu2 tcp_check_req tcp_check_req req->ts_recent = rcv_tsval = t1 req->ts_recent = rcv_tsval = t2
syn_recv_sock tcp_sk(child)->rx_opt.ts_recent = req->ts_recent = t2 // t1 < t2 tcp_child_process tcp_rcv_state_process tcp_validate_incoming tcp_paws_check if ((s32)(rx_opt->ts_recent - rx_opt->rcv_tsval) <= paws_win) // t2 - t1 > paws_win, failed tcp_v4_do_rcv tcp_rcv_state_process // TCP_ESTABLISHED
The cpu2's skb or a newly received skb will call tcp_v4_do_rcv to get the newsk into the TCP_ESTABLISHED state, but at this point it is no longer possible to notify the upper layer application. A notification mechanism could be added here, but the fix is more complex, so the current fix is used.
In tcp_check_req, req->ts_recent is used to assign a value to tcp_sk(child)->rx_opt.ts_recent, so removing the change in req->ts_recent and changing tcp_sk(child)->rx_opt.ts_recent directly after owning the req fixes this bug.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Wang Hai wanghai38@huawei.com Reviewed-by: Jason Xing kerneljasonxing@gmail.com Reviewed-by: Eric Dumazet edumazet@google.com Reviewed-by: Kuniyuki Iwashima kuniyu@amazon.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/tcp_minisocks.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c index 01e27620b7ee5..866055e1b8014 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -726,12 +726,6 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
/* In sequence, PAWS is OK. */
- /* TODO: We probably should defer ts_recent change once - * we take ownership of @req. - */ - if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) - WRITE_ONCE(req->ts_recent, tmp_opt.rcv_tsval); - if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { /* Truncate SYN, it is out of window starting at tcp_rsk(req)->rcv_isn + 1. */ @@ -780,6 +774,10 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, if (!child) goto listen_overflow;
+ if (own_req && tmp_opt.saw_tstamp && + !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) + tcp_sk(child)->rx_opt.ts_recent = tmp_opt.rcv_tsval; + if (own_req && rsk_drop_req(req)) { reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req); inet_csk_reqsk_queue_drop_and_put(sk, req);