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Message-ID: <afc55d46-111e-4536-a885-c5902f993002@embeddedor.com>
Date: Mon, 19 Feb 2024 21:45:00 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Kees Cook <keescook@...omium.org>, Daniel Borkmann <daniel@...earbox.net>
Cc: Mark Rutland <mark.rutland@....com>, Alexei Starovoitov <ast@...nel.org>,
Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
<martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
Yonghong Song <yhs@...com>, John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>,
Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
Haowen Bai <baihaowen@...zu.com>, bpf@...r.kernel.org,
linux-kselftest@...r.kernel.org, Yonghong Song <yonghong.song@...ux.dev>,
Jonathan Corbet <corbet@....net>, "David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>, Jesper Dangaard Brouer <hawk@...nel.org>,
Joanne Koong <joannelkoong@...il.com>, Yafang Shao <laoar.shao@...il.com>,
Kui-Feng Lee <kuifeng@...a.com>, Anton Protopopov <aspsk@...valent.com>,
linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
netdev@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3] bpf: Replace bpf_lpm_trie_key 0-length array with
flexible array
On 2/19/24 17:41, Kees Cook wrote:
> 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.
Yep, this `_hdr` tagged struct adds flexibility (no pun intended :p)
to flexible structures currently nested in the middle of other
structs. We can just use the header members grouped together in the
`_hdr` struct, and avoid embedding the flexible-array member. :)
>
> 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@....com>
> Closes: https://paste.debian.net/hidden/ca500597/
> Signed-off-by: Kees Cook <keescook@...omium.org>
Acked-by: Gustavo A. R. Silva <gustavoars@...nel.org>
Thanks!
--
Gustavo
> ---
> v3- create a new pair of structs -- leave old struct alone
> v2- https://lore.kernel.org/lkml/20240216235536.it.234-kees@kernel.org/
> v1- https://lore.kernel.org/lkml/20230204183241.never.481-kees@kernel.org/
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Andrii Nakryiko <andrii@...nel.org>
> Cc: Martin KaFai Lau <martin.lau@...ux.dev>
> Cc: Song Liu <song@...nel.org>
> Cc: Yonghong Song <yhs@...com>
> Cc: John Fastabend <john.fastabend@...il.com>
> Cc: KP Singh <kpsingh@...nel.org>
> Cc: Stanislav Fomichev <sdf@...gle.com>
> Cc: Hao Luo <haoluo@...gle.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Mykola Lysenko <mykolal@...com>
> Cc: Shuah Khan <shuah@...nel.org>
> Cc: Haowen Bai <baihaowen@...zu.com>
> Cc: bpf@...r.kernel.org
> Cc: linux-kselftest@...r.kernel.org
> ---
> Documentation/bpf/map_lpm_trie.rst | 2 +-
> include/uapi/linux/bpf.h | 14 ++++++++++++-
> 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 | 14 ++++++++++++-
> .../selftests/bpf/progs/map_ptr_kern.c | 2 +-
> tools/testing/selftests/bpf/test_lpm_map.c | 18 ++++++++---------
> 8 files changed, 49 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..c5a46d12076e 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -77,12 +77,24 @@ 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/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..c55244bf1a20 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -77,12 +77,24 @@ 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 */
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