crypto: Replace zero-length array with flexible-array
Subsystems (2)
PATCH 1/1 crypto: Replace zero-length array with flexible-array
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")
--- drivers/crypto/chelsio/chcr_crypto.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
drivers/crypto/chelsio/chcr_crypto.h +4 -4
@@ -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 {
Herbert Xu
maintainerQuoted 31 lines · 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]
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.
Quoted 8 lines
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit76497732932f("cxgb3/l2t: Fix undefined behaviour")Signed-off-by Gustavo A. R. Silva <[email protected]>---
drivers/crypto/chelsio/chcr_crypto.h| 8 ++++----1 file changed, 4 insertions(+), 4 deletions(-)
Please resend via netdev. Thanks.
Signature · 3 lines
Email: Herbert Xu <[email protected]> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt