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kernel: Revert "tcp: do not lock listener to process SYN packets" 

This commit belongs to the patch set (https://lwn.net/Articles/659199/)
that attempts to remove the use of locks on the socket table by
relocating the SYN table to a separate hash table and adding a spin lock
to protect the SYN request queue. Adding only this commit introduces a
race condition for LineageOS kernels for TCP listens, since the TCP SYN
data structures can be corrupted.

A TCP curl bomb on a TCP listen port will corrupt the SYN accept backlog:

for i in $(seq 1 400); do curl -x localhost:443 https://myhost.com -L  --connect-timeout 30 -o /dev/null -sS & done

Run `ss -nltp` and usually the RecVQ column does not drain to 0.

This reverts commit 7d9f104f9cabe1d72a50c4816a48f64fc1da7a64.

This really needs to be reverted across all LineageOS forks:
https://gitlab.com/LineageOS/issues/android/-/issues/3916#note_669493796

Change-Id: Ia7969aeedae411677b307a8e094f9a4cc02b801d
This commit is contained in:
Roger Hu 2021-09-04 09:17:12 -07:00 committed by Nolen Johnson
parent 0b02bd0ec5
commit 7c56badc9a
2 changed files with 2 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
net/ipv4/tcp_ipv4.c
View File

@ -1589,7 +1589,7 @@ static __sum16 tcp_v4_checksum_init(struct sk_buff *skb)
/* The socket must have it's spinlock held when we get
* here, unless it is a TCP_LISTEN socket.
* here.
*
* We have a potential double-lock case here, so even when
* doing backlog processing we use the BH locking scheme.
@ -1728,11 +1728,6 @@ process:
skb->dev = NULL;
if (sk->sk_state == TCP_LISTEN) {
ret = tcp_v4_do_rcv(sk, skb);
goto put_and_return;
}
bh_lock_sock_nested(sk);
tcp_sk(sk)->segs_in += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
ret = 0;
@ -1756,7 +1751,6 @@ process:
}
bh_unlock_sock(sk);
put_and_return:
sock_put(sk);
return ret;

8
net/ipv6/tcp_ipv6.c
View File

@ -1464,7 +1464,7 @@ static __sum16 tcp_v6_checksum_init(struct sk_buff *skb)
}
/* The socket must have it's spinlock held when we get
* here, unless it is a TCP_LISTEN socket.
* here.
*
* We have a potential double-lock case here, so even when
* doing backlog processing we use the BH locking scheme.
@ -1658,11 +1658,6 @@ process:
skb->dev = NULL;
if (sk->sk_state == TCP_LISTEN) {
ret = tcp_v6_do_rcv(sk, skb);
goto put_and_return;
}
bh_lock_sock_nested(sk);
tcp_sk(sk)->segs_in += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
ret = 0;
@ -1686,7 +1681,6 @@ process:
}
bh_unlock_sock(sk);
put_and_return:
sock_put(sk);
return ret ? -1 : 0;