Re: [PATCH] netfilter: nf_conntrack: use get_unaligned_be32() in tcp_sack()

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Mon, May 25, 2026 at 02:58:40PM -0700, Rosen Penev wrote:
> The timestamp-only fast path dereferences the option stream as
> *(__be32 *)ptr, which assumes 4-byte alignment that the TCP option
> stream does not guarantee. Use get_unaligned_be32() instead, which
> reads the value safely and already returns host byte order, so the
> htonl() on the comparison constant can be dropped.
> 
> This matches the existing get_unaligned_be32() use later in the same
> function.
> 
> Assisted-by: Claude:Opus-4.7
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
>  net/netfilter/nf_conntrack_proto_tcp.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
> index b67426c2189b..8993374c9df2 100644
> --- a/net/netfilter/nf_conntrack_proto_tcp.c
> +++ b/net/netfilter/nf_conntrack_proto_tcp.c
> @@ -405,11 +405,11 @@ static void tcp_sack(const struct sk_buff *skb, unsigned int dataoff,
>  		return;
>  
>  	/* Fast path for timestamp-only option */
> -	if (length == TCPOLEN_TSTAMP_ALIGNED
> -	    && *(__be32 *)ptr == htonl((TCPOPT_NOP << 24)
> -				       | (TCPOPT_NOP << 16)
> -				       | (TCPOPT_TIMESTAMP << 8)
> -				       | TCPOLEN_TIMESTAMP))
> +	if (length == TCPOLEN_TSTAMP_ALIGNED &&
> +	    get_unaligned_be32(ptr) == ((TCPOPT_NOP << 24) |
> +					(TCPOPT_NOP << 16) |
> +					(TCPOPT_TIMESTAMP << 8) |
> +					TCPOLEN_TIMESTAMP))

Missing put_unaligned_be32(), BTW.

>  		return;
>  
>  	while (length > 0) {
> -- 
> 2.54.0
>