[PATCH] netfilter: ebtables: fix fortify warnings

[PATCH] netfilter: ebtables: fix fortify warnings

[GONG, Ruiqi]

From: "GONG, Ruiqi" <gongruiqi1@huawei.com>

When compiling with gcc 13 and CONFIG_FORTIFY_SOURCE=y, the following
warning appears:

In function ‘fortify_memcpy_chk’,
    inlined from ‘size_entry_mwt’ at net/bridge/netfilter/ebtables.c:2118:2:
./include/linux/fortify-string.h:592:25: error: call to ‘__read_overflow2_field’
declared with attribute warning: detected read beyond size of field (2nd parameter);
maybe use struct_group()? [-Werror=attribute-warning]
  592 |                         __read_overflow2_field(q_size_field, size);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The compiler is complaining:

memcpy(&offsets[1], &entry->watchers_offset,
                       sizeof(offsets) - sizeof(offsets[0]));

where memcpy reads beyong &entry->watchers_offset to copy
{watchers,target,next}_offset altogether into offsets[]. Silence the
warning by wrapping these three up via struct_group().

Signed-off-by: GONG, Ruiqi <gongruiqi1@huawei.com>
---
 include/uapi/linux/netfilter_bridge/ebtables.h | 14 ++++++++------
 net/bridge/netfilter/ebtables.c                |  3 +--
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/include/uapi/linux/netfilter_bridge/ebtables.h b/include/uapi/linux/netfilter_bridge/ebtables.h
index a494cf43a755..e634da196d08 100644
--- a/include/uapi/linux/netfilter_bridge/ebtables.h
+++ b/include/uapi/linux/netfilter_bridge/ebtables.h
@@ -182,12 +182,14 @@ struct ebt_entry {
 	unsigned char sourcemsk[ETH_ALEN];
 	unsigned char destmac[ETH_ALEN];
 	unsigned char destmsk[ETH_ALEN];
-	/* sizeof ebt_entry + matches */
-	unsigned int watchers_offset;
-	/* sizeof ebt_entry + matches + watchers */
-	unsigned int target_offset;
-	/* sizeof ebt_entry + matches + watchers + target */
-	unsigned int next_offset;
+	struct_group(offsets,
+		/* sizeof ebt_entry + matches */
+		unsigned int watchers_offset;
+		/* sizeof ebt_entry + matches + watchers */
+		unsigned int target_offset;
+		/* sizeof ebt_entry + matches + watchers + target */
+		unsigned int next_offset;
+	);
 	unsigned char elems[0] __attribute__ ((aligned (__alignof__(struct ebt_replace))));
 };
 
diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index 757ec46fc45a..5ec66b1ebb64 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -2115,8 +2115,7 @@ static int size_entry_mwt(const struct ebt_entry *entry, const unsigned char *ba
 		return ret;
 
 	offsets[0] = sizeof(struct ebt_entry); /* matches come first */
-	memcpy(&offsets[1], &entry->watchers_offset,
-			sizeof(offsets) - sizeof(offsets[0]));
+	memcpy(&offsets[1], &entry->offsets, sizeof(offsets) - sizeof(offsets[0]));
 
 	if (state->buf_kern_start) {
 		buf_start = state->buf_kern_start + state->buf_kern_offset;
-- 
2.41.0

Re: [PATCH] netfilter: ebtables: fix fortify warnings

[kernel test robot]

Hi Ruiqi,

kernel test robot noticed the following build errors:

[auto build test ERROR on linus/master]
[also build test ERROR on horms-ipvs/master v6.5-rc5 next-20230808]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/GONG-Ruiqi/netfilter-ebtables-fix-fortify-warnings/20230808-095125
base:   linus/master
patch link:    https://lore.kernel.org/r/20230808014821.241688-1-gongruiqi%40huaweicloud.com
patch subject: [PATCH] netfilter: ebtables: fix fortify warnings
config: i386-randconfig-r011-20230808 (https://download.01.org/0day-ci/archive/20230808/202308081840.VN5BvVWf-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce: (https://download.01.org/0day-ci/archive/20230808/202308081840.VN5BvVWf-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202308081840.VN5BvVWf-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from <command-line>:
>> ./usr/include/linux/netfilter_bridge/ebtables.h:185:9: error: expected specifier-qualifier-list before 'struct_group'
     185 |         struct_group(offsets,
         |         ^~~~~~~~~~~~
   ./usr/include/linux/netfilter_bridge/ebtables.h: In function 'ebt_get_target':
>> ./usr/include/linux/netfilter_bridge/ebtables.h:199:57: error: 'struct ebt_entry' has no member named 'target_offset'
     199 |         return (struct ebt_entry_target *)((char *)e + e->target_offset);
         |                                                         ^~

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH] netfilter: ebtables: fix fortify warnings

[Florian Westphal]

GONG, Ruiqi <gongruiqi@huaweicloud.com> wrote:
> From: "GONG, Ruiqi" <gongruiqi1@huawei.com>
> 
> When compiling with gcc 13 and CONFIG_FORTIFY_SOURCE=y, the following
> warning appears:
> 
> In function ‘fortify_memcpy_chk’,
>     inlined from ‘size_entry_mwt’ at net/bridge/netfilter/ebtables.c:2118:2:
> ./include/linux/fortify-string.h:592:25: error: call to ‘__read_overflow2_field’
> declared with attribute warning: detected read beyond size of field (2nd parameter);
> maybe use struct_group()? [-Werror=attribute-warning]
>   592 |                         __read_overflow2_field(q_size_field, size);
>       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> The compiler is complaining:
> 
> memcpy(&offsets[1], &entry->watchers_offset,
>                        sizeof(offsets) - sizeof(offsets[0]));
> 
> where memcpy reads beyong &entry->watchers_offset to copy
> {watchers,target,next}_offset altogether into offsets[]. Silence the
> warning by wrapping these three up via struct_group().
> 
> Signed-off-by: GONG, Ruiqi <gongruiqi1@huawei.com>
> ---
>  include/uapi/linux/netfilter_bridge/ebtables.h | 14 ++++++++------
>  net/bridge/netfilter/ebtables.c                |  3 +--
>  2 files changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/include/uapi/linux/netfilter_bridge/ebtables.h b/include/uapi/linux/netfilter_bridge/ebtables.h
> index a494cf43a755..e634da196d08 100644
> --- a/include/uapi/linux/netfilter_bridge/ebtables.h
> +++ b/include/uapi/linux/netfilter_bridge/ebtables.h
> @@ -182,12 +182,14 @@ struct ebt_entry {
>  	unsigned char sourcemsk[ETH_ALEN];
>  	unsigned char destmac[ETH_ALEN];
>  	unsigned char destmsk[ETH_ALEN];
> -	/* sizeof ebt_entry + matches */
> -	unsigned int watchers_offset;
> -	/* sizeof ebt_entry + matches + watchers */
> -	unsigned int target_offset;
> -	/* sizeof ebt_entry + matches + watchers + target */
> -	unsigned int next_offset;
> +	struct_group(offsets,
> +		/* sizeof ebt_entry + matches */

This is an UAPI header, I think you need to use __struct_group here.

Re: [PATCH] netfilter: ebtables: fix fortify warnings

[GONG, Ruiqi]

On 2023/08/08 23:54, Florian Westphal wrote:
> 
> [...]
>>
>> diff --git a/include/uapi/linux/netfilter_bridge/ebtables.h b/include/uapi/linux/netfilter_bridge/ebtables.h
>> index a494cf43a755..e634da196d08 100644
>> --- a/include/uapi/linux/netfilter_bridge/ebtables.h
>> +++ b/include/uapi/linux/netfilter_bridge/ebtables.h
>> @@ -182,12 +182,14 @@ struct ebt_entry {
>>  	unsigned char sourcemsk[ETH_ALEN];
>>  	unsigned char destmac[ETH_ALEN];
>>  	unsigned char destmsk[ETH_ALEN];
>> -	/* sizeof ebt_entry + matches */
>> -	unsigned int watchers_offset;
>> -	/* sizeof ebt_entry + matches + watchers */
>> -	unsigned int target_offset;
>> -	/* sizeof ebt_entry + matches + watchers + target */
>> -	unsigned int next_offset;
>> +	struct_group(offsets,
>> +		/* sizeof ebt_entry + matches */
> 
> This is an UAPI header, I think you need to use __struct_group here.

Thanks for the reminder! I've fixed it in v2:

https://lore.kernel.org/all/20230808133038.771316-1-gongruiqi@huaweicloud.com/

Please review it :)