[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-ID: <202308162257.F7876776C9@keescook>
Date: Wed, 16 Aug 2023 23:09:00 -0700
From: Kees Cook <keescook@...omium.org>
To: "GONG, Ruiqi" <gongruiqi1@...wei.com>
Cc: kernel test robot <lkp@...el.com>, llvm@...ts.linux.dev,
oe-kbuild-all@...ts.linux.dev, Florian Westphal <fw@...len.de>,
linux-hardening@...r.kernel.org
Subject: Re: [netfilter-nf-next:testing 2/9]
./usr/include/linux/netfilter_bridge/ebtables.h:163:26: warning: field
'target' with variable sized type 'struct ebt_entry_target' not at the end
of a struct or class is a GNU extension
On Thu, Aug 17, 2023 at 01:03:20PM +0800, kernel test robot wrote:
> tree: git://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf-next.git testing
> head: 015e2d9101d3713c7bee16dccad171df04a3bbd5
> commit: 61b9e6bd48a6317c0a44ee4f3fecdec9de5baa9e [2/9] netfilter: ebtables: replace zero-length array members
> config: i386-buildonly-randconfig-r004-20230817 (https://download.01.org/0day-ci/archive/20230817/202308171249.g1ywxhII-lkp@intel.com/config)
> compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
> reproduce: (https://download.01.org/0day-ci/archive/20230817/202308171249.g1ywxhII-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@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202308171249.g1ywxhII-lkp@intel.com/
>
> All warnings (new ones prefixed by >>):
>
> In file included from <built-in>:1:
> >> ./usr/include/linux/netfilter_bridge/ebtables.h:163:26: warning: field 'target' with variable sized type 'struct ebt_entry_target' not at the end of a struct or class is a GNU extension [-Wgnu-variable-sized-type-not-at-end]
> struct ebt_entry_target target;
> ^
> 1 warning generated.
Eww, it looks like "struct ebt_entry_target" is used _within_ another
struct:
struct ebt_standard_target {
struct ebt_entry_target target;
int verdict;
};
So "verdict" overlaps with the "data" FAM:
struct ebt_entry_target {
union {
struct {
char name[EBT_EXTENSION_MAXNAMELEN];
__u8 revision;
};
struct xt_target *target;
} u;
/* size of data */
unsigned int target_size;
unsigned char data[0] __attribute__ ((aligned (__alignof__(struct ebt_replace))));
};
These have been fixed in the past in a variety of ways -- it all depends
on how userspace is using them. In looking at Debian Code Search:
https://codesearch.debian.net/search?q=struct+ebt_standard_target&literal=1
It is exclusively doing casts and looking at the "verdict" member. So
the easiest conversion might be this:
struct ebt_standard_target {
- struct ebt_entry_target target;
+ unsigned char hdr[sizeof(struct ebt_entry_target)];
int verdict;
};
Or this might work (not tested):
diff --git a/include/uapi/linux/netfilter_bridge/ebtables.h b/include/uapi/linux/netfilter_bridge/ebtables.h
index a494cf43a755..d6f10163b14a 100644
--- a/include/uapi/linux/netfilter_bridge/ebtables.h
+++ b/include/uapi/linux/netfilter_bridge/ebtables.h
@@ -146,23 +146,25 @@ struct ebt_entry_watcher {
};
struct ebt_entry_target {
- union {
- struct {
- char name[EBT_EXTENSION_MAXNAMELEN];
- __u8 revision;
- };
- struct xt_target *target;
- } u;
- /* size of data */
- unsigned int target_size;
- unsigned char data[0] __attribute__ ((aligned (__alignof__(struct ebt_replace))));
+ struct ebt_entry_target_hdr {
+ union {
+ struct {
+ char name[EBT_EXTENSION_MAXNAMELEN];
+ __u8 revision;
+ };
+ struct xt_target *target;
+ } u;
+ /* size of data */
+ unsigned int target_size;
+ };
+ unsigned char data[] __attribute__ ((aligned (__alignof__(struct ebt_replace))));
};
#define EBT_STANDARD_TARGET "standard"
struct ebt_standard_target {
- struct ebt_entry_target target;
- int verdict;
+ struct ebt_entry_target_hdr target;
+ int verdict __attribute__ ((aligned (__alignof__(struct ebt_replace))));
};
/* one entry */
--
Kees Cook
Powered by blists - more mailing lists