Re: [PATCH] net: ipv6: rpl_iptunnel: Replace 0-length arrays with flexible arrays

[David Ahern <dsahern@kernel.org>]

On 1/5/23 3:15 PM, Kees Cook wrote:
> Zero-length arrays are deprecated[1]. Replace struct ipv6_rpl_sr_hdr's
> "segments" union of 0-length arrays with flexible arrays. Detected with
> GCC 13, using -fstrict-flex-arrays=3:
> 
> In function 'rpl_validate_srh',
>     inlined from 'rpl_build_state' at ../net/ipv6/rpl_iptunnel.c:96:7:
> ../net/ipv6/rpl_iptunnel.c:60:28: warning: array subscript <unknown> is outside array bounds of 'struct in6_addr[0]' [-Warray-bounds=]
>    60 |         if (ipv6_addr_type(&srh->rpl_segaddr[srh->segments_left - 1]) &
>       |                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> In file included from ../include/net/rpl.h:12,
>                  from ../net/ipv6/rpl_iptunnel.c:13:
> ../include/uapi/linux/rpl.h: In function 'rpl_build_state':
> ../include/uapi/linux/rpl.h:40:33: note: while referencing 'addr'
>    40 |                 struct in6_addr addr[0];
>       |                                 ^~~~
> 
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays
> 
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
> Cc: David Ahern <dsahern@kernel.org>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Cc: netdev@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  include/uapi/linux/rpl.h | 4 ++--
>  net/ipv6/rpl_iptunnel.c  | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 

Reviewed-by: David Ahern <dsahern@kernel.org>