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* [PATCH] crypto: Replace zero-length array with flexible-array
@ 2020-05-07 18:51 Gustavo A. R. Silva
  2020-05-15  6:08 ` Herbert Xu
  0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-05-07 18:51 UTC (permalink / raw)
  To: Ayush Sawal, Vinay Kumar Yadav, Rohit Maheshwari
  Cc: linux-crypto, linux-kernel

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]

sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.

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 <gustavoars@kernel.org>
---
 drivers/crypto/chelsio/chcr_crypto.h |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/crypto/chelsio/chcr_crypto.h b/drivers/crypto/chelsio/chcr_crypto.h
index 542bebae001f..1cc522a07aac 100644
--- a/drivers/crypto/chelsio/chcr_crypto.h
+++ b/drivers/crypto/chelsio/chcr_crypto.h
@@ -223,7 +223,7 @@ struct chcr_authenc_ctx {
 
 struct __aead_ctx {
 	struct chcr_gcm_ctx gcm[0];
-	struct chcr_authenc_ctx authenc[0];
+	struct chcr_authenc_ctx authenc[];
 };
 
 struct chcr_aead_ctx {
@@ -235,7 +235,7 @@ struct chcr_aead_ctx {
 	u8 nonce[4];
 	u16 hmac_ctrl;
 	u16 mayverify;
-	struct	__aead_ctx ctx[0];
+	struct	__aead_ctx ctx[];
 };
 
 struct hmac_ctx {
@@ -247,7 +247,7 @@ struct hmac_ctx {
 struct __crypto_ctx {
 	struct hmac_ctx hmacctx[0];
 	struct ablk_ctx ablkctx[0];
-	struct chcr_aead_ctx aeadctx[0];
+	struct chcr_aead_ctx aeadctx[];
 };
 
 struct chcr_context {
@@ -257,7 +257,7 @@ struct chcr_context {
 	unsigned int  ntxq;
 	unsigned int  nrxq;
 	struct completion cbc_aes_aio_done;
-	struct __crypto_ctx crypto_ctx[0];
+	struct __crypto_ctx crypto_ctx[];
 };
 
 struct chcr_hctx_per_wr {


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [PATCH] crypto: Replace zero-length array with flexible-array
  2020-05-07 18:51 [PATCH] crypto: Replace zero-length array with flexible-array Gustavo A. R. Silva
@ 2020-05-15  6:08 ` Herbert Xu
  0 siblings, 0 replies; 2+ messages in thread
From: Herbert Xu @ 2020-05-15  6:08 UTC (permalink / raw)
  To: Gustavo A. R. Silva
  Cc: ayush.sawal, vinay.yadav, rohitm, linux-crypto, linux-kernel

Gustavo A. R. Silva <gustavoars@kernel.org> 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]
> 
> sizeof(flexible-array-member) triggers a warning because flexible array
> members have incomplete type[1]. There are some instances of code in
> which the sizeof operator is being incorrectly/erroneously applied to
> zero-length arrays and the result is zero. Such instances may be hiding
> some bugs. So, this work (flexible-array member conversions) will also
> help to get completely rid of those sorts of issues.
> 
> 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 <gustavoars@kernel.org>
> ---
> drivers/crypto/chelsio/chcr_crypto.h |    8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)

Please resend via netdev.  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

^ permalink raw reply	[flat|nested] 2+ messages in thread

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2020-05-07 18:51 [PATCH] crypto: Replace zero-length array with flexible-array Gustavo A. R. Silva
2020-05-15  6:08 ` Herbert Xu

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