Commit 896880ff authored by Kees Cook's avatar Kees Cook Committed by Daniel Borkmann
Browse files

bpf: Replace bpf_lpm_trie_key 0-length array with flexible array 



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.

Reported-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarGustavo A. R. Silva <gustavoars@kernel.org>
Closes: https://paste.debian.net/hidden/ca500597/
Link: https://lore.kernel.org/all/202206281009.4332AA33@keescook/ [1]
Link: https://lore.kernel.org/bpf/20240222155612.it.533-kees@kernel.org
parent b9a62998

Documentation/bpf/map_lpm_trie.rst

+1 −1
Original line number Diff line number Diff line
@@ -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

include/uapi/linux/bpf.h

+18 −1
Original line number Diff line number Diff line
@@ -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) */

kernel/bpf/lpm_trie.c

+10 −10
Original line number Diff line number Diff line
@@ -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;

}

samples/bpf/map_perf_test_user.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

samples/bpf/xdp_router_ipv4_user.c

+1 −1
Original line number Diff line number Diff line
@@ -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;