On 5/14/25 3:56 PM, chia-yu.chang@xxxxxxxxxxxxxxxxxxx wrote:
> From: Ilpo Järvinen <ij@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Signed-off-by: Chia-Yu Chang <chia-yu.chang@xxxxxxxxxxxxxxxxxxx>
> ---
> net/ipv4/tcp_output.c | 23 ++++++++++++-----------
> 1 file changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index d0f0fee8335e..d7fef3d2698b 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -1092,17 +1092,18 @@ 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;
> -
> - 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;
> + 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);
> +
> + size += TCPOLEN_SACK_BASE_ALIGNED +
> + opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
> + }
> + } else {
> + opts->num_sack_blocks = 0;
> }
AFAICS here opts->num_sack_blocks is still uninitialized when:
eff_acks != 0 &&
remaining < (TCPOLEN_SACK_BASE_ALIGNED + TCPOLEN_SACK_PERBLOCK)
/P
