[PATCH][next] firewire: Replace zero-length array with flexible-array member

[PATCH][next] firewire: Replace zero-length array with flexible-array member

[Gustavo A. R. Silva]

Zero-length and one-element arrays are deprecated, and we are moving
towards adopting C99 flexible-array members, instead.

Address the following warnings found with GCC-13 and
-fstrict-flex-arrays=3 enabled:
sound/firewire/amdtp-stream.c: In function ‘build_it_pkt_header’:
sound/firewire/amdtp-stream.c:694:17: warning: ‘generate_cip_header’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
  694 |                 generate_cip_header(s, cip_header, data_block_counter, syt);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
sound/firewire/amdtp-stream.c:694:17: note: referencing argument 2 of type ‘__be32[2]’ {aka ‘unsigned int[2]’}
sound/firewire/amdtp-stream.c:667:13: note: in a call to function ‘generate_cip_header’
  667 | static void generate_cip_header(struct amdtp_stream *s, __be32 cip_header[2],
      |             ^~~~~~~~~~~~~~~~~~~

This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
routines on memcpy() and help us make progress towards globally
enabling -fstrict-flex-arrays=3 [1].

Link: https://github.com/KSPP/linux/issues/21
Link: https://github.com/KSPP/linux/issues/303
Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 include/linux/firewire.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/firewire.h b/include/linux/firewire.h
index 1716c01c4e54..efb6e2cf2034 100644
--- a/include/linux/firewire.h
+++ b/include/linux/firewire.h
@@ -391,7 +391,7 @@ struct fw_iso_packet {
 	u32 tag:2;		/* tx: Tag in packet header		*/
 	u32 sy:4;		/* tx: Sy in packet header		*/
 	u32 header_length:8;	/* Length of immediate header		*/
-	u32 header[0];		/* tx: Top of 1394 isoch. data_block	*/
+	u32 header[];		/* tx: Top of 1394 isoch. data_block	*/
 };
 
 #define FW_ISO_CONTEXT_TRANSMIT			0
-- 
2.34.1

Re: [PATCH][next] firewire: Replace zero-length array with flexible-array member

[Takashi Sakamoto]

Hi,

On Mon, May 29, 2023 at 12:52:07PM -0600, Gustavo A. R. Silva wrote:
> Zero-length and one-element arrays are deprecated, and we are moving
> towards adopting C99 flexible-array members, instead.
> 
> Address the following warnings found with GCC-13 and
> -fstrict-flex-arrays=3 enabled:
> sound/firewire/amdtp-stream.c: In function ‘build_it_pkt_header’:
> sound/firewire/amdtp-stream.c:694:17: warning: ‘generate_cip_header’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
>   694 |                 generate_cip_header(s, cip_header, data_block_counter, syt);
>       |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> sound/firewire/amdtp-stream.c:694:17: note: referencing argument 2 of type ‘__be32[2]’ {aka ‘unsigned int[2]’}
> sound/firewire/amdtp-stream.c:667:13: note: in a call to function ‘generate_cip_header’
>   667 | static void generate_cip_header(struct amdtp_stream *s, __be32 cip_header[2],
>       |             ^~~~~~~~~~~~~~~~~~~
> 
> This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
> routines on memcpy() and help us make progress towards globally
> enabling -fstrict-flex-arrays=3 [1].
> 
> Link: https://github.com/KSPP/linux/issues/21
> Link: https://github.com/KSPP/linux/issues/303
> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
>  include/linux/firewire.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Thanks for the patch. I applied it to for-linus branch as a fix for
v6.4-rc4, instead of for-next branch.

* https://git.kernel.org/ieee1394/linux1394/c/41dd10a086c5


Thanks

Takashi Sakamoto

Re: [PATCH][next] firewire: Replace zero-length array with flexible-array member

[Kees Cook]

On Mon, May 29, 2023 at 12:52:07PM -0600, Gustavo A. R. Silva wrote:
> Zero-length and one-element arrays are deprecated, and we are moving
> towards adopting C99 flexible-array members, instead.
> 
> Address the following warnings found with GCC-13 and
> -fstrict-flex-arrays=3 enabled:
> sound/firewire/amdtp-stream.c: In function ‘build_it_pkt_header’:
> sound/firewire/amdtp-stream.c:694:17: warning: ‘generate_cip_header’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
>   694 |                 generate_cip_header(s, cip_header, data_block_counter, syt);
>       |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> sound/firewire/amdtp-stream.c:694:17: note: referencing argument 2 of type ‘__be32[2]’ {aka ‘unsigned int[2]’}
> sound/firewire/amdtp-stream.c:667:13: note: in a call to function ‘generate_cip_header’
>   667 | static void generate_cip_header(struct amdtp_stream *s, __be32 cip_header[2],
>       |             ^~~~~~~~~~~~~~~~~~~
> 
> This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
> routines on memcpy() and help us make progress towards globally
> enabling -fstrict-flex-arrays=3 [1].
> 
> Link: https://github.com/KSPP/linux/issues/21
> Link: https://github.com/KSPP/linux/issues/303
> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook