6.1-stable review patch. If anyone has any objections, please let me know.
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From: John Fastabend john.fastabend@gmail.com
[ Upstream commit 9b7177b1df64b8d7f85700027c324aadd6aded00 ]
Before fix e5c6de5fa0258 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: e5c6de5fa0258 ("bpf, sockmap: Incorrectly handling copied_seq") Fixes: 04919bed948dc ("tcp: Introduce tcp_read_skb()") Signed-off-by: John Fastabend john.fastabend@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: Jakub Sitnicki jakub@cloudflare.com Link: https://lore.kernel.org/bpf/20230926035300.135096-2-john.fastabend@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/tcp.c | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index fab25d4f3a6f1..96fdde6e42b1b 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1755,16 +1755,13 @@ EXPORT_SYMBOL(tcp_read_sock);
int tcp_read_skb(struct sock *sk, skb_read_actor_t recv_actor) { - struct tcp_sock *tp = tcp_sk(sk); - u32 seq = tp->copied_seq; struct sk_buff *skb; int copied = 0; - u32 offset;
if (sk->sk_state == TCP_LISTEN) return -ENOTCONN;
- while ((skb = tcp_recv_skb(sk, seq, &offset)) != NULL) { + while ((skb = skb_peek(&sk->sk_receive_queue)) != NULL) { u8 tcp_flags; int used;
@@ -1777,13 +1774,10 @@ int tcp_read_skb(struct sock *sk, skb_read_actor_t recv_actor) copied = used; break; } - seq += used; copied += used;
- if (tcp_flags & TCPHDR_FIN) { - ++seq; + if (tcp_flags & TCPHDR_FIN) break; - } } return copied; }