netdev - Re: [PATCH] net: ipv4: Avoid bounds check warning

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Date:   Thu, 26 May 2022 10:22:25 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Genjian Zhang <zhanggenjian123@...il.com>, edumazet@...gle.com,
        davem@...emloft.net, yoshfuji@...ux-ipv6.org, dsahern@...nel.org,
        kuba@...nel.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        huhai@...inos.cn
Subject: Re: [PATCH] net: ipv4: Avoid bounds check warning

On Tue, 2022-05-24 at 15:23 +0800, Genjian Zhang wrote:
> From: huhai <huhai@...inos.cn>
> 
> Fix the following build warning when CONFIG_IPV6 is not set:
> 
> In function ‘fortify_memcpy_chk’,
>     inlined from ‘tcp_md5_do_add’ at net/ipv4/tcp_ipv4.c:1211:2:
> ./include/linux/fortify-string.h:328:4: error: call to ‘__write_overflow_field’ declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
>   328 |    __write_overflow_field(p_size_field, size);
>       |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Signed-off-by: huhai <huhai@...inos.cn>
> ---
>  net/ipv4/tcp_ipv4.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index 457f5b5d5d4a..ed03b8c48443 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1207,9 +1207,14 @@ int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
>  	key->prefixlen = prefixlen;
>  	key->l3index = l3index;
>  	key->flags = flags;
> +#if IS_ENABLED(CONFIG_IPV6)
>  	memcpy(&key->addr, addr,
>  	       (family == AF_INET6) ? sizeof(struct in6_addr) :
>  				      sizeof(struct in_addr));

I'm wondering if you could avoid the extra compiler conditional with
something alike:

 	memcpy(&key->addr, addr,
  	       (IS_ENABLED(CONFIG_IPV6) && family == AF_INET6) ? sizeof(struct in6_addr) :
								 sizeof(struct in_addr));

Thanks!

Paolo