From 70f1451ec98ee43d2c66d2caa5ae6935ee97f90a Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Mon, 23 Mar 2020 19:08:58 -0500 Subject: [PATCH] posix_acl.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/posix_acl.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/posix_acl.h b/include/linux/posix_acl.h index 540595a321a7..90797f1b421d 100644 --- a/include/linux/posix_acl.h +++ b/include/linux/posix_acl.h @@ -28,7 +28,7 @@ struct posix_acl { refcount_t a_refcount; struct rcu_head a_rcu; unsigned int a_count; - struct posix_acl_entry a_entries[0]; + struct posix_acl_entry a_entries[]; }; #define FOREACH_ACL_ENTRY(pa, acl, pe) \ -- 2.34.1