From 6805fc79f8dc39bfc90aaa4cd5b9c2cc470320a6 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Thu, 30 Apr 2020 23:30:47 +0200 Subject: [PATCH] bpf: Avoid gcc-10 stringop-overflow warning in struct bpf_prog gcc-10 warns about accesses to zero-length arrays: kernel/bpf/core.c: In function 'bpf_patch_insn_single': cc1: warning: writing 8 bytes into a region of size 0 [-Wstringop-overflow=] In file included from kernel/bpf/core.c:21: include/linux/filter.h:550:20: note: at offset 0 to object 'insnsi' with size 0 declared here 550 | struct bpf_insn insnsi[0]; | ^~~~~~ In this case, we really want to have two flexible-array members, but that is not possible. Removing the union to make insnsi a flexible-array member while leaving insns as a zero-length array fixes the warning, as nothing writes to the other one in that way. This trick only works on linux-3.18 or higher, as older versions had additional members in the union. Fixes: 073a09ee970b ("net: bpf: make eBPF interpreter images read-only") Signed-off-by: Arnd Bergmann Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20200430213101.135134-6-arnd@arndb.de --- include/linux/filter.h | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/include/linux/filter.h b/include/linux/filter.h index af37318bb1c56..73d06a39e2d61 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -545,10 +545,8 @@ struct bpf_prog { unsigned int (*bpf_func)(const void *ctx, const struct bpf_insn *insn); /* Instructions for interpreter */ - union { - struct sock_filter insns[0]; - struct bpf_insn insnsi[0]; - }; + struct sock_filter insns[0]; + struct bpf_insn insnsi[]; }; struct sk_filter { -- 2.39.5