[PATCH] etherdevice: Adjust ether_addr* prototypes to silence -Wstringop-overead

[PATCH] etherdevice: Adjust ether_addr* prototypes to silence -Wstringop-overead

[Kees Cook]

With GCC 12, -Wstringop-overread was warning about an implicit cast from
char[6] to char[8]. However, the extra 2 bytes are always thrown away,
alignment doesn't matter, and the risk of hitting the edge of unallocated
memory has been accepted, so this prototype can just be converted to a
regular char *. Silences:

net/core/dev.c: In function ‘bpf_prog_run_generic_xdp’: net/core/dev.c:4618:21: warning: ‘ether_addr_equal_64bits’ reading 8 bytes from a region of size 6 [-Wstringop-overread]
 4618 |         orig_host = ether_addr_equal_64bits(eth->h_dest, > skb->dev->dev_addr);
      |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
net/core/dev.c:4618:21: note: referencing argument 1 of type ‘const u8[8]’ {aka ‘const unsigned char[8]’}
net/core/dev.c:4618:21: note: referencing argument 2 of type ‘const u8[8]’ {aka ‘const unsigned char[8]’}
In file included from net/core/dev.c:91: include/linux/etherdevice.h:375:20: note: in a call to function ‘ether_addr_equal_64bits’
  375 | static inline bool ether_addr_equal_64bits(const u8 addr1[6+2],
      |                    ^~~~~~~~~~~~~~~~~~~~~~~

Reported-by: Marc Kleine-Budde <mkl@pengutronix.de>
Tested-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/netdev/20220212090811.uuzk6d76agw2vv73@pengutronix.de
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 include/linux/etherdevice.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/include/linux/etherdevice.h b/include/linux/etherdevice.h
index 2ad71cc90b37..92b10e67d5f8 100644
--- a/include/linux/etherdevice.h
+++ b/include/linux/etherdevice.h
@@ -134,7 +134,7 @@ static inline bool is_multicast_ether_addr(const u8 *addr)
 #endif
 }
 
-static inline bool is_multicast_ether_addr_64bits(const u8 addr[6+2])
+static inline bool is_multicast_ether_addr_64bits(const u8 *addr)
 {
 #if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64
 #ifdef __BIG_ENDIAN
@@ -372,8 +372,7 @@ static inline bool ether_addr_equal(const u8 *addr1, const u8 *addr2)
  * Please note that alignment of addr1 & addr2 are only guaranteed to be 16 bits.
  */
 
-static inline bool ether_addr_equal_64bits(const u8 addr1[6+2],
-					   const u8 addr2[6+2])
+static inline bool ether_addr_equal_64bits(const u8 *addr1, const u8 *addr2)
 {
 #if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64
 	u64 fold = (*(const u64 *)addr1) ^ (*(const u64 *)addr2);
-- 
2.30.2

Re: [PATCH] etherdevice: Adjust ether_addr* prototypes to silence -Wstringop-overead

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (master)
by David S. Miller <davem@davemloft.net>:

On Sat, 12 Feb 2022 09:14:49 -0800 you wrote:
> With GCC 12, -Wstringop-overread was warning about an implicit cast from
> char[6] to char[8]. However, the extra 2 bytes are always thrown away,
> alignment doesn't matter, and the risk of hitting the edge of unallocated
> memory has been accepted, so this prototype can just be converted to a
> regular char *. Silences:
> 
> net/core/dev.c: In function ‘bpf_prog_run_generic_xdp’: net/core/dev.c:4618:21: warning: ‘ether_addr_equal_64bits’ reading 8 bytes from a region of size 6 [-Wstringop-overread]
>  4618 |         orig_host = ether_addr_equal_64bits(eth->h_dest, > skb->dev->dev_addr);
>       |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> net/core/dev.c:4618:21: note: referencing argument 1 of type ‘const u8[8]’ {aka ‘const unsigned char[8]’}
> net/core/dev.c:4618:21: note: referencing argument 2 of type ‘const u8[8]’ {aka ‘const unsigned char[8]’}
> In file included from net/core/dev.c:91: include/linux/etherdevice.h:375:20: note: in a call to function ‘ether_addr_equal_64bits’
>   375 | static inline bool ether_addr_equal_64bits(const u8 addr1[6+2],
>       |                    ^~~~~~~~~~~~~~~~~~~~~~~
> 
> [...]

Here is the summary with links:
  - etherdevice: Adjust ether_addr* prototypes to silence -Wstringop-overead
    https://git.kernel.org/netdev/net-next/c/2618a0dae09e

You are awesome, thank you!
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