* [PATCH] crypto: img-hash - Replace zero-length array with flexible-array member
@ 2020-02-13 16:50 Gustavo A. R. Silva
2020-02-22 1:43 ` Herbert Xu
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-13 16:50 UTC (permalink / raw)
To: Herbert Xu, David S. Miller
Cc: linux-crypto, linux-kernel, Gustavo A. R. Silva
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
drivers/crypto/img-hash.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/crypto/img-hash.c b/drivers/crypto/img-hash.c
index 25d5227f74a1..0e25fc3087f3 100644
--- a/drivers/crypto/img-hash.c
+++ b/drivers/crypto/img-hash.c
@@ -103,7 +103,7 @@ struct img_hash_request_ctx {
struct ahash_request fallback_req;
/* Zero length buffer must remain last member of struct */
- u8 buffer[0] __aligned(sizeof(u32));
+ u8 buffer[] __aligned(sizeof(u32));
};
struct img_hash_ctx {
--
2.25.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] crypto: img-hash - Replace zero-length array with flexible-array member
2020-02-13 16:50 [PATCH] crypto: img-hash - Replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-02-22 1:43 ` Herbert Xu
0 siblings, 0 replies; 2+ messages in thread
From: Herbert Xu @ 2020-02-22 1:43 UTC (permalink / raw)
To: Gustavo A. R. Silva; +Cc: David S. Miller, linux-crypto, linux-kernel
On Thu, Feb 13, 2020 at 10:50:54AM -0600, Gustavo A. R. Silva wrote:
> The current codebase makes use of the zero-length array language
> extension to the C90 standard, but the preferred mechanism to declare
> variable-length types such as these ones is a flexible array member[1][2],
> introduced in C99:
>
> struct foo {
> int stuff;
> struct boo array[];
> };
>
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertently introduced[3] to the codebase from now on.
>
> Also, notice that, dynamic memory allocations won't be affected by
> this change:
>
> "Flexible array members have incomplete type, and so the sizeof operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
>
> This issue was found with the help of Coccinelle.
>
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
> drivers/crypto/img-hash.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
Patch applied. Thanks.
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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