Replace deprecated 0-length array in struct bpf_lpm_trie_key with flexible array. Found with GCC 13:

../kernel/bpf/lpm_trie.c:207:51: warning: array subscript i is outside array bounds of 'const __u8[0]' {aka 'const unsigned char[]'} [-Warray-bounds=] 207 | *(__be16 *)&key->data[i]); | ^~~~~~~~~~~~~ ../include/uapi/linux/swab.h:102:54: note: in definition of macro '__swab16' 102 | #define __swab16(x) (__u16)__builtin_bswap16((__u16)(x)) | ^ ../include/linux/byteorder/generic.h:97:21: note: in expansion of macro '__be16_to_cpu' 97 | #define be16_to_cpu __be16_to_cpu | ^~~~~~~~~~~~~ ../kernel/bpf/lpm_trie.c:206:28: note: in expansion of macro 'be16_to_cpu' 206 | u16 diff = be16_to_cpu(*(__be16 *)&node->data[i] ^ | ^~~~~~~~~~~ In file included from ../include/linux/bpf.h:7: ../include/uapi/linux/bpf.h:82:17: note: while referencing 'data' 82 | __u8 data[0]; /* Arbitrary size */ | ^~~~

And found at run-time under CONFIG_FORTIFY_SOURCE:

UBSAN: array-index-out-of-bounds in kernel/bpf/lpm_trie.c:218:49 index 0 is out of range for type '__u8 [*]'

Changing struct bpf_lpm_trie_key is difficult since has been used by userspace. For example, in Cilium:

struct egress_gw_policy_key { struct bpf_lpm_trie_key lpm_key; __u32 saddr; __u32 daddr; };

While direct references to the "data" member haven't been found, there are static initializers what include the final member. For example, the "{}" here:

struct egress_gw_policy_key in_key = { .lpm_key = { 32 + 24, {} }, .saddr = CLIENT_IP, .daddr = EXTERNAL_SVC_IP & 0Xffffff, };

To avoid the build time and run time warnings seen with a 0-sized trailing array for struct bpf_lpm_trie_key, introduce a new struct that correctly uses a flexible array for the trailing bytes, struct bpf_lpm_trie_key_u8. As part of this, include the "header" portion (which is just the "prefixlen" member), so it can be used by anything building a bpf_lpr_trie_key that has trailing members that aren't a u8 flexible array (like the self-test[1]), which is named struct bpf_lpm_trie_key_hdr.

Unfortunately, C++ refuses to parse the __struct_group() helper, so it is not possible to define struct bpf_lpm_trie_key_hdr directly in struct bpf_lpm_trie_key_u8, so we must open-code the union directly.

Adjust the kernel code to use struct bpf_lpm_trie_key_u8 through-out, and for the selftest to use struct bpf_lpm_trie_key_hdr. Add a comment to the UAPI header directing folks to the two new options.

Link: https://lore.kernel.org/all/202206281009.4332AA33@keescook/ [1] Reported-by: Mark Rutland mark.rutland@arm.com Closes: https://paste.debian.net/hidden/ca500597/ Acked-by: Gustavo A. R. Silva gustavoars@kernel.org Signed-off-by: Kees Cook keescook@chromium.org --- Cc: Daniel Borkmann daniel@iogearbox.net Cc: Alexei Starovoitov ast@kernel.org Cc: Andrii Nakryiko andrii@kernel.org Cc: Martin KaFai Lau martin.lau@linux.dev Cc: Song Liu song@kernel.org Cc: Yonghong Song yhs@fb.com Cc: John Fastabend john.fastabend@gmail.com Cc: KP Singh kpsingh@kernel.org Cc: Stanislav Fomichev sdf@google.com Cc: Hao Luo haoluo@google.com Cc: Jiri Olsa jolsa@kernel.org Cc: Mykola Lysenko mykolal@fb.com Cc: Shuah Khan shuah@kernel.org Cc: Haowen Bai baihaowen@meizu.com Cc: bpf@vger.kernel.org Cc: linux-kselftest@vger.kernel.org v5- remove __struct_group() usage, which C++ appears to be allergic to. v4- https://lore.kernel.org/lkml/20240220185421.it.949-kees@kernel.org/ v3- https://lore.kernel.org/lkml/20240219234121.make.373-kees@kernel.org/ v2- https://lore.kernel.org/lkml/20240216235536.it.234-kees@kernel.org/ v1- https://lore.kernel.org/lkml/20230204183241.never.481-kees@kernel.org/ --- Documentation/bpf/map_lpm_trie.rst | 2 +- include/uapi/linux/bpf.h | 19 +++++++++++++++++- kernel/bpf/lpm_trie.c | 20 +++++++++---------- samples/bpf/map_perf_test_user.c | 2 +- samples/bpf/xdp_router_ipv4_user.c | 2 +- tools/include/uapi/linux/bpf.h | 15 +++++++++++++- .../selftests/bpf/progs/map_ptr_kern.c | 2 +- tools/testing/selftests/bpf/test_lpm_map.c | 18 ++++++++--------- 8 files changed, 55 insertions(+), 25 deletions(-)

diff --git a/Documentation/bpf/map_lpm_trie.rst b/Documentation/bpf/map_lpm_trie.rst index 74d64a30f500..f9cd579496c9 100644 --- a/Documentation/bpf/map_lpm_trie.rst +++ b/Documentation/bpf/map_lpm_trie.rst @@ -17,7 +17,7 @@ significant byte.

LPM tries may be created with a maximum prefix length that is a multiple of 8, in the range from 8 to 2048. The key used for lookup and update -operations is a ``struct bpf_lpm_trie_key``, extended by +operations is a ``struct bpf_lpm_trie_key_u8``, extended by ``max_prefixlen/8`` bytes.

- For IPv4 addresses the data length is 4 bytes diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 754e68ca8744..2241d894f952 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -77,12 +77,29 @@ struct bpf_insn { __s32 imm; /* signed immediate constant */ };

-/* Key of an a BPF_MAP_TYPE_LPM_TRIE entry */ +/* Deprecated: use struct bpf_lpm_trie_key_u8 (when the "data" member is needed for + * byte access) or struct bpf_lpm_trie_key_hdr (when using an alternative type for + * the trailing flexible array member) instead. + */ struct bpf_lpm_trie_key { __u32 prefixlen; /* up to 32 for AF_INET, 128 for AF_INET6 */ __u8 data[0]; /* Arbitrary size */ };

+/* Header for bpf_lpm_trie_key structs */ +struct bpf_lpm_trie_key_hdr { + __u32 prefixlen; +}; + +/* Key of an a BPF_MAP_TYPE_LPM_TRIE entry, with trailing byte array. */ +struct bpf_lpm_trie_key_u8 { + union { + struct bpf_lpm_trie_key_hdr hdr; + __u32 prefixlen; + }; + __u8 data[]; /* Arbitrary size */ +}; + struct bpf_cgroup_storage_key { __u64 cgroup_inode_id; /* cgroup inode id */ __u32 attach_type; /* program attach type (enum bpf_attach_type) */ diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c index b32be680da6c..050fe1ebf0f7 100644 --- a/kernel/bpf/lpm_trie.c +++ b/kernel/bpf/lpm_trie.c @@ -164,13 +164,13 @@ static inline int extract_bit(const u8 *data, size_t index) */ static size_t longest_prefix_match(const struct lpm_trie *trie, const struct lpm_trie_node *node, - const struct bpf_lpm_trie_key *key) + const struct bpf_lpm_trie_key_u8 *key) { u32 limit = min(node->prefixlen, key->prefixlen); u32 prefixlen = 0, i = 0;

BUILD_BUG_ON(offsetof(struct lpm_trie_node, data) % sizeof(u32)); - BUILD_BUG_ON(offsetof(struct bpf_lpm_trie_key, data) % sizeof(u32)); + BUILD_BUG_ON(offsetof(struct bpf_lpm_trie_key_u8, data) % sizeof(u32));

#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && defined(CONFIG_64BIT)

@@ -229,7 +229,7 @@ static void *trie_lookup_elem(struct bpf_map *map, void *_key) { struct lpm_trie *trie = container_of(map, struct lpm_trie, map); struct lpm_trie_node *node, *found = NULL; - struct bpf_lpm_trie_key *key = _key; + struct bpf_lpm_trie_key_u8 *key = _key;

if (key->prefixlen > trie->max_prefixlen) return NULL; @@ -309,7 +309,7 @@ static long trie_update_elem(struct bpf_map *map, struct lpm_trie *trie = container_of(map, struct lpm_trie, map); struct lpm_trie_node *node, *im_node = NULL, *new_node = NULL; struct lpm_trie_node __rcu **slot; - struct bpf_lpm_trie_key *key = _key; + struct bpf_lpm_trie_key_u8 *key = _key; unsigned long irq_flags; unsigned int next_bit; size_t matchlen = 0; @@ -437,7 +437,7 @@ static long trie_update_elem(struct bpf_map *map, static long trie_delete_elem(struct bpf_map *map, void *_key) { struct lpm_trie *trie = container_of(map, struct lpm_trie, map); - struct bpf_lpm_trie_key *key = _key; + struct bpf_lpm_trie_key_u8 *key = _key; struct lpm_trie_node __rcu **trim, **trim2; struct lpm_trie_node *node, *parent; unsigned long irq_flags; @@ -536,7 +536,7 @@ static long trie_delete_elem(struct bpf_map *map, void *_key) sizeof(struct lpm_trie_node)) #define LPM_VAL_SIZE_MIN 1

-#define LPM_KEY_SIZE(X) (sizeof(struct bpf_lpm_trie_key) + (X)) +#define LPM_KEY_SIZE(X) (sizeof(struct bpf_lpm_trie_key_u8) + (X)) #define LPM_KEY_SIZE_MAX LPM_KEY_SIZE(LPM_DATA_SIZE_MAX) #define LPM_KEY_SIZE_MIN LPM_KEY_SIZE(LPM_DATA_SIZE_MIN)

@@ -565,7 +565,7 @@ static struct bpf_map *trie_alloc(union bpf_attr *attr) /* copy mandatory map attributes */ bpf_map_init_from_attr(&trie->map, attr); trie->data_size = attr->key_size - - offsetof(struct bpf_lpm_trie_key, data); + offsetof(struct bpf_lpm_trie_key_u8, data); trie->max_prefixlen = trie->data_size * 8;

spin_lock_init(&trie->lock); @@ -616,7 +616,7 @@ static int trie_get_next_key(struct bpf_map *map, void *_key, void *_next_key) { struct lpm_trie_node *node, *next_node = NULL, *parent, *search_root; struct lpm_trie *trie = container_of(map, struct lpm_trie, map); - struct bpf_lpm_trie_key *key = _key, *next_key = _next_key; + struct bpf_lpm_trie_key_u8 *key = _key, *next_key = _next_key; struct lpm_trie_node **node_stack = NULL; int err = 0, stack_ptr = -1; unsigned int next_bit; @@ -703,7 +703,7 @@ static int trie_get_next_key(struct bpf_map *map, void *_key, void *_next_key) } do_copy: next_key->prefixlen = next_node->prefixlen; - memcpy((void *)next_key + offsetof(struct bpf_lpm_trie_key, data), + memcpy((void *)next_key + offsetof(struct bpf_lpm_trie_key_u8, data), next_node->data, trie->data_size); free_stack: kfree(node_stack); @@ -715,7 +715,7 @@ static int trie_check_btf(const struct bpf_map *map, const struct btf_type *key_type, const struct btf_type *value_type) { - /* Keys must have struct bpf_lpm_trie_key embedded. */ + /* Keys must have struct bpf_lpm_trie_key_u8 embedded. */ return BTF_INFO_KIND(key_type->info) != BTF_KIND_STRUCT ? -EINVAL : 0; } diff --git a/samples/bpf/map_perf_test_user.c b/samples/bpf/map_perf_test_user.c index d2fbcf963cdf..07ff471ed6ae 100644 --- a/samples/bpf/map_perf_test_user.c +++ b/samples/bpf/map_perf_test_user.c @@ -370,7 +370,7 @@ static void run_perf_test(int tasks)

static void fill_lpm_trie(void) { - struct bpf_lpm_trie_key *key; + struct bpf_lpm_trie_key_u8 *key; unsigned long value = 0; unsigned int i; int r; diff --git a/samples/bpf/xdp_router_ipv4_user.c b/samples/bpf/xdp_router_ipv4_user.c index 9d41db09c480..266fdd0b025d 100644 --- a/samples/bpf/xdp_router_ipv4_user.c +++ b/samples/bpf/xdp_router_ipv4_user.c @@ -91,7 +91,7 @@ static int recv_msg(struct sockaddr_nl sock_addr, int sock) static void read_route(struct nlmsghdr *nh, int nll) { char dsts[24], gws[24], ifs[16], dsts_len[24], metrics[24]; - struct bpf_lpm_trie_key *prefix_key; + struct bpf_lpm_trie_key_u8 *prefix_key; struct rtattr *rt_attr; struct rtmsg *rt_msg; int rtm_family; diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 7f24d898efbb..76b1b41c0dce 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -8,6 +8,7 @@ #ifndef _UAPI__LINUX_BPF_H__ #define _UAPI__LINUX_BPF_H__

+#include <linux/stddef.h> #include <linux/types.h> #include <linux/bpf_common.h>

@@ -77,12 +78,24 @@ struct bpf_insn { __s32 imm; /* signed immediate constant */ };

-/* Key of an a BPF_MAP_TYPE_LPM_TRIE entry */ +/* Deprecated: use struct bpf_lpm_trie_key_u8 (when the "data" member is needed for + * byte access) or struct bpf_lpm_trie_key_hdr (when using an alternative type for + * the trailing flexible array member) instead. + */ struct bpf_lpm_trie_key { __u32 prefixlen; /* up to 32 for AF_INET, 128 for AF_INET6 */ __u8 data[0]; /* Arbitrary size */ };

+/* Key of an a BPF_MAP_TYPE_LPM_TRIE entry, with trailing byte array. */ +struct bpf_lpm_trie_key_u8 { + __struct_group(bpf_lpm_trie_key_hdr, hdr, /* no attrs */, + /* up to 32 for AF_INET, 128 for AF_INET6 */ + __u32 prefixlen; + ); + __u8 data[]; /* Arbitrary size */ +}; + struct bpf_cgroup_storage_key { __u64 cgroup_inode_id; /* cgroup inode id */ __u32 attach_type; /* program attach type (enum bpf_attach_type) */ diff --git a/tools/testing/selftests/bpf/progs/map_ptr_kern.c b/tools/testing/selftests/bpf/progs/map_ptr_kern.c index 3325da17ec81..efaf622c28dd 100644 --- a/tools/testing/selftests/bpf/progs/map_ptr_kern.c +++ b/tools/testing/selftests/bpf/progs/map_ptr_kern.c @@ -316,7 +316,7 @@ struct lpm_trie { } __attribute__((preserve_access_index));

struct lpm_key { - struct bpf_lpm_trie_key trie_key; + struct bpf_lpm_trie_key_hdr trie_key; __u32 data; };

diff --git a/tools/testing/selftests/bpf/test_lpm_map.c b/tools/testing/selftests/bpf/test_lpm_map.c index c028d621c744..d98c72dc563e 100644 --- a/tools/testing/selftests/bpf/test_lpm_map.c +++ b/tools/testing/selftests/bpf/test_lpm_map.c @@ -211,7 +211,7 @@ static void test_lpm_map(int keysize) volatile size_t n_matches, n_matches_after_delete; size_t i, j, n_nodes, n_lookups; struct tlpm_node *t, *list = NULL; - struct bpf_lpm_trie_key *key; + struct bpf_lpm_trie_key_u8 *key; uint8_t *data, *value; int r, map;

@@ -331,8 +331,8 @@ static void test_lpm_map(int keysize) static void test_lpm_ipaddr(void) { LIBBPF_OPTS(bpf_map_create_opts, opts, .map_flags = BPF_F_NO_PREALLOC); - struct bpf_lpm_trie_key *key_ipv4; - struct bpf_lpm_trie_key *key_ipv6; + struct bpf_lpm_trie_key_u8 *key_ipv4; + struct bpf_lpm_trie_key_u8 *key_ipv6; size_t key_size_ipv4; size_t key_size_ipv6; int map_fd_ipv4; @@ -423,7 +423,7 @@ static void test_lpm_ipaddr(void) static void test_lpm_delete(void) { LIBBPF_OPTS(bpf_map_create_opts, opts, .map_flags = BPF_F_NO_PREALLOC); - struct bpf_lpm_trie_key *key; + struct bpf_lpm_trie_key_u8 *key; size_t key_size; int map_fd; __u64 value; @@ -532,7 +532,7 @@ static void test_lpm_delete(void) static void test_lpm_get_next_key(void) { LIBBPF_OPTS(bpf_map_create_opts, opts, .map_flags = BPF_F_NO_PREALLOC); - struct bpf_lpm_trie_key *key_p, *next_key_p; + struct bpf_lpm_trie_key_u8 *key_p, *next_key_p; size_t key_size; __u32 value = 0; int map_fd; @@ -693,9 +693,9 @@ static void *lpm_test_command(void *arg) { int i, j, ret, iter, key_size; struct lpm_mt_test_info *info = arg; - struct bpf_lpm_trie_key *key_p; + struct bpf_lpm_trie_key_u8 *key_p;

- key_size = sizeof(struct bpf_lpm_trie_key) + sizeof(__u32); + key_size = sizeof(*key_p) + sizeof(__u32); key_p = alloca(key_size); for (iter = 0; iter < info->iter; iter++) for (i = 0; i < MAX_TEST_KEYS; i++) { @@ -717,7 +717,7 @@ static void *lpm_test_command(void *arg) ret = bpf_map_lookup_elem(info->map_fd, key_p, &value); assert(ret == 0 || errno == ENOENT); } else { - struct bpf_lpm_trie_key *next_key_p = alloca(key_size); + struct bpf_lpm_trie_key_u8 *next_key_p = alloca(key_size); ret = bpf_map_get_next_key(info->map_fd, key_p, next_key_p); assert(ret == 0 || errno == ENOENT || errno == ENOMEM); } @@ -752,7 +752,7 @@ static void test_lpm_multi_thread(void)

/* create a trie */ value_size = sizeof(__u32); - key_size = sizeof(struct bpf_lpm_trie_key) + value_size; + key_size = sizeof(struct bpf_lpm_trie_key_hdr) + value_size; map_fd = bpf_map_create(BPF_MAP_TYPE_LPM_TRIE, NULL, key_size, value_size, 100, &opts);

/* create 4 threads to test update, delete, lookup and get_next_key */