Re: [PATCH net-next] tcp: Fix tcp_syn_flood_action() if CONFIG_IPV6=n

[Matthieu Baerts <matthieu.baerts@tessares.net>]

Hi Geert,

On 15/11/2022 11:12, Geert Uytterhoeven wrote:
> If CONFIG_IPV6=n:
> 
>     net/ipv4/tcp_input.c: In function ‘tcp_syn_flood_action’:
>     include/net/sock.h:387:37: error: ‘const struct sock_common’ has no member named ‘skc_v6_rcv_saddr’; did you mean ‘skc_rcv_saddr’?
>       387 | #define sk_v6_rcv_saddr __sk_common.skc_v6_rcv_saddr
> 	  |                                     ^~~~~~~~~~~~~~~~
>     include/linux/printk.h:429:19: note: in definition of macro ‘printk_index_wrap’
>       429 |   _p_func(_fmt, ##__VA_ARGS__);    \
> 	  |                   ^~~~~~~~~~~
>     include/linux/printk.h:530:2: note: in expansion of macro ‘printk’
>       530 |  printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)
> 	  |  ^~~~~~
>     include/linux/net.h:272:3: note: in expansion of macro ‘pr_info’
>       272 |   function(__VA_ARGS__);    \
> 	  |   ^~~~~~~~
>     include/linux/net.h:288:2: note: in expansion of macro ‘net_ratelimited_function’
>       288 |  net_ratelimited_function(pr_info, fmt, ##__VA_ARGS__)
> 	  |  ^~~~~~~~~~~~~~~~~~~~~~~~
>     include/linux/net.h:288:43: note: in expansion of macro ‘sk_v6_rcv_saddr’
>       288 |  net_ratelimited_function(pr_info, fmt, ##__VA_ARGS__)
> 	  |                                           ^~~~~~~~~~~
>     net/ipv4/tcp_input.c:6847:4: note: in expansion of macro ‘net_info_ratelimited’
>      6847 |    net_info_ratelimited("%s: Possible SYN flooding on port [%pI6c]:%u. %s.\n",
> 	  |    ^~~~~~~~~~~~~~~~~~~~
> 
> Fix this by using "#if" instead of "if", like is done for all other
> checks for CONFIG_IPV6.

Thank you for the patch!

Our CI validating MPTCP also found the issue. I was going to suggest a
similar one before I saw yours :)

Everything is fixed on my side after having applied the patch!

Tested-by: Matthieu Baerts <matthieu.baerts@tessares.net>

> Fixes: d9282e48c6088105 ("tcp: Add listening address to SYN flood message")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
>  net/ipv4/tcp_input.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 94024fdc2da1b28a..e5d7a33fac6666bb 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -6843,11 +6843,14 @@ static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
>  
>  	if (!queue->synflood_warned && syncookies != 2 &&
>  	    xchg(&queue->synflood_warned, 1) == 0) {
> -		if (IS_ENABLED(CONFIG_IPV6) && sk->sk_family == AF_INET6) {
> +#if IS_ENABLED(CONFIG_IPV6)
> +		if (sk->sk_family == AF_INET6) {
>  			net_info_ratelimited("%s: Possible SYN flooding on port [%pI6c]:%u. %s.\n",
>  					proto, &sk->sk_v6_rcv_saddr,
>  					sk->sk_num, msg);
> -		} else {
> +		} else
> +#endif
> +		{

I was going to suggest to remove the unneeded braces here and just
before + eventually fix the indentation under net_info_ratelimited()
while at it but that's just some details not directly linked to the fix
here.

Cheers,
Matt
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