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tcp: sack option handling improvements 

1) Don't early return when sack doesn't fit. AccECN code will be
   placed after this fragment so no early returns please.

2) Make sure opts->num_sack_blocks is not left undefined. E.g.,
   tcp_current_mss() does not memset its opts struct to zero.
   AccECN code checks if SACK option is present and may even
   alter it to make room for AccECN option when many SACK blocks
   are present. Thus, num_sack_blocks needs to be always valid.

Signed-off-by: Ilpo Järvinen <ij@kernel.org>
Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250916082434.100722-6-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Ilpo Järvinen 2025-09-16 10:24:29 +02:00 committed by Paolo Abeni
parent a92543d597
commit 77a4fdf43c
1 changed files with 13 additions and 10 deletions
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23
net/ipv4/tcp_output.c
View File

@ -985,17 +985,20 @@ static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb
eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
if (unlikely(eff_sacks)) {
const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
if (unlikely(remaining < TCPOLEN_SACK_BASE_ALIGNED +
TCPOLEN_SACK_PERBLOCK))
return size;
if (likely(remaining >= TCPOLEN_SACK_BASE_ALIGNED +
TCPOLEN_SACK_PERBLOCK)) {
opts->num_sack_blocks =
min_t(unsigned int, eff_sacks,
(remaining - TCPOLEN_SACK_BASE_ALIGNED) /
TCPOLEN_SACK_PERBLOCK);
opts->num_sack_blocks =
min_t(unsigned int, eff_sacks,
(remaining - TCPOLEN_SACK_BASE_ALIGNED) /
TCPOLEN_SACK_PERBLOCK);
size += TCPOLEN_SACK_BASE_ALIGNED +
opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
size += TCPOLEN_SACK_BASE_ALIGNED +
opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
} else {
opts->num_sack_blocks = 0;
}
} else {
opts->num_sack_blocks = 0;
}
if (unlikely(BPF_SOCK_OPS_TEST_FLAG(tp,