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  1. 29 Sep, 2023 2 commits
    • John Fastabend's avatar
      bpf, sockmap: Do not inc copied_seq when PEEK flag set · da9e915e
      John Fastabend authored 
      When data is peek'd off the receive queue we shouldn't considered it
copied from tcp_sock side. When we increment copied_seq this will confuse
tcp_data_ready() because copied_seq can be arbitrarily increased. From
application side it results in poll() operations not waking up when
expected.

Notice tcp stack without BPF recvmsg programs also does not increment
copied_seq.

We broke this when we moved copied_seq into recvmsg to only update when
actual copy was happening. But, it wasn't working correctly either before
because the tcp_data_ready() tried to use the copied_seq value to see
if data was read by user yet. See fixes tags.

Fixes: e5c6de5f ("bpf, sockmap: Incorrectly handling copied_seq")
Fixes: 04919bed ("tcp: Introduce tcp_read_skb()")
Signed-off-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarJakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20230926035300.135096-3-john.fastabend@gmail.com
      da9e915e
    • John Fastabend's avatar
      bpf: tcp_read_skb needs to pop skb regardless of seq · 9b7177b1
      John Fastabend authored 
      Before fix e5c6de5f tcp_read_skb() would increment the tp->copied-seq
value. This (as described in the commit) would cause an error for apps
because once that is incremented the application might believe there is no
data to be read. Then some apps would stall or abort believing no data is
available.

However, the fix is incomplete because it introduces another issue in
the skb dequeue. The loop does tcp_recv_skb() in a while loop to consume
as many skbs as possible. The problem is the call is ...

  tcp_recv_skb(sk, seq, &offset)

... where 'seq' is:

  u32 seq = tp->copied_seq;

Now we can hit a case where we've yet incremented copied_seq from BPF side,
but then tcp_recv_skb() fails this test ...

 if (offset < skb->len || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))

... so that instead of returning the skb we call tcp_eat_recv_skb() which
frees the skb. This is because the routine believes the SKB has been collapsed
per comment:

 /* This looks weird, but this can happen if TCP collapsing
  * splitted a fat GRO packet, while we released socket lock
  * in skb_splice_bits()
  */

This can't happen here we've unlinked the full SKB and orphaned it. Anyways
it would confuse any BPF programs if the data were suddenly moved underneath
it.

To fix this situation do simpler operation and just skb_peek() the data
of the queue followed by the unlink. It shouldn't need to check this
condition and tcp_read_skb() reads entire skbs so there is no need to
handle the 'offset!=0' case as we would see in tcp_read_sock().

Fixes: e5c6de5f ("bpf, sockmap: Incorrectly handling copied_seq")
Fixes: 04919bed ("tcp: Introduce tcp_read_skb()")
Signed-off-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarJakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20230926035300.135096-2-john.fastabend@gmail.com
      9b7177b1
  3. 20 Sep, 2023 1 commit
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  13. 15 Sep, 2023 3 commits
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