On Fri, Jan 6, 2023 at 5:28 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> Zero-length arrays are deprecated[1]. Replace struct ethtool_rxnfc's
> "rule_locs" 0-length array with a flexible array. Detected with GCC 13,
> using -fstrict-flex-arrays=3:
>
> net/ethtool/common.c: In function 'ethtool_get_max_rxnfc_channel':
> net/ethtool/common.c:558:55: warning: array subscript i is outside array bounds of '__u32[0]' {aka 'unsigned int[]'} [-Warray-bounds=]
> 558 | .fs.location = info->rule_locs[i],
> | ~~~~~~~~~~~~~~~^~~
> In file included from include/linux/ethtool.h:19,
> from include/uapi/linux/ethtool_netlink.h:12,
> from include/linux/ethtool_netlink.h:6,
> from net/ethtool/common.c:3:
> include/uapi/linux/ethtool.h:1186:41: note: while referencing
> 'rule_locs'
> 1186 | __u32 rule_locs[0];
> | ^~~~~~~~~
>
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays
>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Andrew Lunn <andrew@xxxxxxx>
> Cc: kernel test robot <lkp@xxxxxxxxx>
> Cc: Oleksij Rempel <linux@xxxxxxxxxxxxxxxx>
> Cc: Sean Anderson <sean.anderson@xxxxxxxx>
> Cc: Alexandru Tachici <alexandru.tachici@xxxxxxxxxx>
> Cc: Amit Cohen <amcohen@xxxxxxxxxx>
> Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
> Cc: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> v3: don't use helper (vincent)
> v2: https://lore.kernel.org/lkml/20230105233420.gonna.036-kees@xxxxxxxxxx
> ---
> include/uapi/linux/ethtool.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/ethtool.h b/include/uapi/linux/ethtool.h
> index 58e587ba0450..3135fa0ba9a4 100644
> --- a/include/uapi/linux/ethtool.h
> +++ b/include/uapi/linux/ethtool.h
> @@ -1183,7 +1183,7 @@ struct ethtool_rxnfc {
> __u32 rule_cnt;
> __u32 rss_context;
> };
> - __u32 rule_locs[0];
> + __u32 rule_locs[];
Stupid question: Is this syntax allowed in UAPI headers despite not
being part of standard C90 or C++? Are we relying on all C/C++
compilers for pre-C99 having gcc/clang extensions?
