[v2] jbd2: Avoid dozens of -Wflex-array-member-not-at-end warnings

[PATCH v2][next] jbd2: Avoid dozens of -Wflex-array-member-not-at-end warnings

Posted by Gustavo A. R. Silva 3 weeks, 1 day ago

-Wflex-array-member-not-at-end was introduced in GCC-14, and we
are getting ready to enable it, globally.

Use the `DEFINE_RAW_FLEX()` helper for an on-stack definition of
a flexible structure (`struct shash_desc`) where the size of the
flexible-array member (`__ctx`) is known at compile-time, and
refactor the rest of the code, accordingly.

So, with this, fix 77 of the following warnings:

include/linux/jbd2.h:1800:35: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
Changes in v2:
 - Use DIV_ROUND_UP() to compute the number of elements for the flex
   array. (Jan Kara)

v1:
 - Link: https://lore.kernel.org/linux-hardening/ZxvyavDjXDaV9cNg@kspp/

 include/linux/jbd2.h | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 8aef9bb6ad57..50f7ea8714bf 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -1796,22 +1796,21 @@ static inline unsigned long jbd2_log_space_left(journal_t *journal)
 static inline u32 jbd2_chksum(journal_t *journal, u32 crc,
 			      const void *address, unsigned int length)
 {
-	struct {
-		struct shash_desc shash;
-		char ctx[JBD_MAX_CHECKSUM_SIZE];
-	} desc;
+	DEFINE_RAW_FLEX(struct shash_desc, desc, __ctx,
+		DIV_ROUND_UP(JBD_MAX_CHECKSUM_SIZE,
+			     sizeof(*((struct shash_desc *)0)->__ctx)));
 	int err;
 
 	BUG_ON(crypto_shash_descsize(journal->j_chksum_driver) >
 		JBD_MAX_CHECKSUM_SIZE);
 
-	desc.shash.tfm = journal->j_chksum_driver;
-	*(u32 *)desc.ctx = crc;
+	desc->tfm = journal->j_chksum_driver;
+	*(u32 *)desc->__ctx = crc;
 
-	err = crypto_shash_update(&desc.shash, address, length);
+	err = crypto_shash_update(desc, address, length);
 	BUG_ON(err);
 
-	return *(u32 *)desc.ctx;
+	return *(u32 *)desc->__ctx;
 }
 
 /* Return most recent uncommitted transaction */
-- 
2.43.0

Re: [PATCH v2][next] jbd2: Avoid dozens of -Wflex-array-member-not-at-end warnings

Posted by Theodore Ts'o 1 week, 3 days ago

On Fri, 01 Nov 2024 14:45:23 -0600, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we
> are getting ready to enable it, globally.
> 
> Use the `DEFINE_RAW_FLEX()` helper for an on-stack definition of
> a flexible structure (`struct shash_desc`) where the size of the
> flexible-array member (`__ctx`) is known at compile-time, and
> refactor the rest of the code, accordingly.
> 
> [...]

Applied, thanks!

[1/1] jbd2: Avoid dozens of -Wflex-array-member-not-at-end warnings
      commit: 2bd9077b6261b8f1281d0fa74d51afe090319263

Best regards,
-- 
Theodore Ts'o <tytso@mit.edu>

Re: [PATCH v2][next] jbd2: Avoid dozens of -Wflex-array-member-not-at-end warnings

Posted by Jan Kara 2 weeks, 6 days ago

On Fri 01-11-24 14:45:23, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we
> are getting ready to enable it, globally.
> 
> Use the `DEFINE_RAW_FLEX()` helper for an on-stack definition of
> a flexible structure (`struct shash_desc`) where the size of the
> flexible-array member (`__ctx`) is known at compile-time, and
> refactor the rest of the code, accordingly.
> 
> So, with this, fix 77 of the following warnings:
> 
> include/linux/jbd2.h:1800:35: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
> Changes in v2:
>  - Use DIV_ROUND_UP() to compute the number of elements for the flex
>    array. (Jan Kara)
> 
> v1:
>  - Link: https://lore.kernel.org/linux-hardening/ZxvyavDjXDaV9cNg@kspp/
> 
>  include/linux/jbd2.h | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 8aef9bb6ad57..50f7ea8714bf 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -1796,22 +1796,21 @@ static inline unsigned long jbd2_log_space_left(journal_t *journal)
>  static inline u32 jbd2_chksum(journal_t *journal, u32 crc,
>  			      const void *address, unsigned int length)
>  {
> -	struct {
> -		struct shash_desc shash;
> -		char ctx[JBD_MAX_CHECKSUM_SIZE];
> -	} desc;
> +	DEFINE_RAW_FLEX(struct shash_desc, desc, __ctx,
> +		DIV_ROUND_UP(JBD_MAX_CHECKSUM_SIZE,
> +			     sizeof(*((struct shash_desc *)0)->__ctx)));
>  	int err;
>  
>  	BUG_ON(crypto_shash_descsize(journal->j_chksum_driver) >
>  		JBD_MAX_CHECKSUM_SIZE);
>  
> -	desc.shash.tfm = journal->j_chksum_driver;
> -	*(u32 *)desc.ctx = crc;
> +	desc->tfm = journal->j_chksum_driver;
> +	*(u32 *)desc->__ctx = crc;
>  
> -	err = crypto_shash_update(&desc.shash, address, length);
> +	err = crypto_shash_update(desc, address, length);
>  	BUG_ON(err);
>  
> -	return *(u32 *)desc.ctx;
> +	return *(u32 *)desc->__ctx;
>  }
>  
>  /* Return most recent uncommitted transaction */
> -- 
> 2.43.0
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR