From c61a2a76e5da267d8f5070a34c074d104155c0f6 Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Fri, 28 Feb 2020 18:51:41 -0600 Subject: [PATCH] net: ipv6: mld: 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 Signed-off-by: David S. Miller --- include/net/mld.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/net/mld.h b/include/net/mld.h index b0f5b3105ef0..496bddb59942 100644 --- a/include/net/mld.h +++ b/include/net/mld.h @@ -24,12 +24,12 @@ struct mld2_grec { __u8 grec_auxwords; __be16 grec_nsrcs; struct in6_addr grec_mca; - struct in6_addr grec_src[0]; + struct in6_addr grec_src[]; }; struct mld2_report { struct icmp6hdr mld2r_hdr; - struct mld2_grec mld2r_grec[0]; + struct mld2_grec mld2r_grec[]; }; #define mld2r_type mld2r_hdr.icmp6_type @@ -55,7 +55,7 @@ struct mld2_query { #endif __u8 mld2q_qqic; __be16 mld2q_nsrcs; - struct in6_addr mld2q_srcs[0]; + struct in6_addr mld2q_srcs[]; }; #define mld2q_type mld2q_hdr.icmp6_type