From d7f10df86202273155a9d8f8553bc2ad28e0dd46 Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Wed, 26 Feb 2020 18:17:44 -0600 Subject: [PATCH] bpf: 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: Daniel Borkmann Acked-by: Song Liu Link: https://lore.kernel.org/bpf/20200227001744.GA3317@embeddedor --- include/linux/bpf-cgroup.h | 2 +- include/linux/bpf.h | 2 +- include/uapi/linux/bpf.h | 2 +- kernel/bpf/bpf_struct_ops.c | 2 +- kernel/bpf/hashtab.c | 2 +- kernel/bpf/lpm_trie.c | 2 +- 6 files changed, 6 insertions(+), 6 deletions(-) diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h index a11d5b7..a7cd5c7 100644 --- a/include/linux/bpf-cgroup.h +++ b/include/linux/bpf-cgroup.h @@ -36,7 +36,7 @@ struct bpf_cgroup_storage_map; struct bpf_storage_buffer { struct rcu_head rcu; - char data[0]; + char data[]; }; struct bpf_cgroup_storage { diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 1acd5bf..9aa33b8 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -859,7 +859,7 @@ struct bpf_prog_array_item { struct bpf_prog_array { struct rcu_head rcu; - struct bpf_prog_array_item items[0]; + struct bpf_prog_array_item items[]; }; struct bpf_prog_array *bpf_prog_array_alloc(u32 prog_cnt, gfp_t flags); diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 906e9f2..8e98ced 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -73,7 +73,7 @@ struct bpf_insn { /* Key of an a BPF_MAP_TYPE_LPM_TRIE entry */ struct bpf_lpm_trie_key { __u32 prefixlen; /* up to 32 for AF_INET, 128 for AF_INET6 */ - __u8 data[0]; /* Arbitrary size */ + __u8 data[]; /* Arbitrary size */ }; struct bpf_cgroup_storage_key { diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c index 042f955..c498f0f 100644 --- a/kernel/bpf/bpf_struct_ops.c +++ b/kernel/bpf/bpf_struct_ops.c @@ -23,7 +23,7 @@ enum bpf_struct_ops_state { struct bpf_struct_ops_value { BPF_STRUCT_OPS_COMMON_VALUE; - char data[0] ____cacheline_aligned_in_smp; + char data[] ____cacheline_aligned_in_smp; }; struct bpf_struct_ops_map { diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index 53d9483..d541c84 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -118,7 +118,7 @@ struct htab_elem { struct bpf_lru_node lru_node; }; u32 hash; - char key[0] __aligned(8); + char key[] __aligned(8); }; static inline bool htab_is_prealloc(const struct bpf_htab *htab) diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c index 3b3c420..65c236c 100644 --- a/kernel/bpf/lpm_trie.c +++ b/kernel/bpf/lpm_trie.c @@ -25,7 +25,7 @@ struct lpm_trie_node { struct lpm_trie_node __rcu *child[2]; u32 prefixlen; u32 flags; - u8 data[0]; + u8 data[]; }; struct lpm_trie { -- 2.7.4