From 1fa0949bede6de2b595da535c3ce69de8e130db2 Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Mon, 23 Mar 2020 17:03:49 -0500 Subject: [PATCH] digsig.h: Replace zero-length array with flexible-array member 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 --- include/linux/digsig.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/digsig.h b/include/linux/digsig.h index 594fc66a395a..2ace69e41088 100644 --- a/include/linux/digsig.h +++ b/include/linux/digsig.h @@ -29,7 +29,7 @@ struct pubkey_hdr { uint32_t timestamp; /* key made, always 0 for now */ uint8_t algo; uint8_t nmpi; - char mpi[0]; + char mpi[]; } __packed; struct signature_hdr { @@ -39,7 +39,7 @@ struct signature_hdr { uint8_t hash; uint8_t keyid[8]; uint8_t nmpi; - char mpi[0]; + char mpi[]; } __packed; #if defined(CONFIG_SIGNATURE) || defined(CONFIG_SIGNATURE_MODULE) -- 2.30.2