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Kees Cook d9a429fec7 bpf: Replace bpf_lpm_trie_key 0-length array with flexible array 
[ Upstream commit 896880ff30866f386ebed14ab81ce1ad3710cfc4 ]

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: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Gustavo 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
Stable-dep-of: 59f2f841179a ("bpf: Avoid kfree_rcu() under lock in bpf_lpm_trie.")
Signed-off-by: Sasha Levin <sashal@kernel.org>
2024-08-29 17:30:22 +02:00
..
libbpf bpf, docs: Remove deprecated xsk libbpf APIs description 2022-07-08 14:18:50 +02:00
bpf_design_QA.rst bpf: Update bpf_design_QA.rst to clarify that BTF_ID does not ABIify a function 2022-08-04 13:17:24 -07:00
bpf_devel_QA.rst docs: netdev: move the netdev-FAQ to the process pages 2022-03-31 10:49:39 +02:00
bpf_licensing.rst bpf: Document BPF licensing. 2021-09-22 23:13:13 +02:00
bpf_prog_run.rst Documentation/bpf: Add documentation for BPF_PROG_RUN 2022-03-09 14:19:22 -08:00
btf.rst docs/bpf: Update documentation for BTF_KIND_FUNC 2022-07-19 09:42:09 -07:00
clang-notes.rst bpf, docs: Add Clang note about BPF_ALU 2022-09-30 13:41:25 -07:00
classic_vs_extended.rst bpf, docs: Split the comparism to classic BPF from instruction-set.rst 2021-12-30 16:31:44 -08:00
drgn.rst bpf: Document bpf_inspect drgn tool 2020-03-26 00:08:36 +01:00
faq.rst bpf, docs: Fix ordering of bpf documentation 2021-11-17 23:24:01 +01:00
helpers.rst bpf, docs: Fix ordering of bpf documentation 2021-11-17 23:24:01 +01:00
index.rst Documentation: bpf: Add implementation notes documentations to table of contents 2022-10-03 09:16:52 -07:00
instruction-set.rst bpf, docs: Fix modulo zero, division by zero, overflow, and underflow 2023-03-10 09:33:50 +01:00
kfuncs.rst bpf: Tweak definition of KF_TRUSTED_ARGS 2022-09-21 19:25:26 -07:00
linux-notes.rst bpf, docs: Delete misformatted table. 2022-10-01 08:51:26 -07:00
llvm_reloc.rst bpf, docs: Add llvm_reloc.rst to explain llvm bpf relocations 2021-05-28 22:12:04 +02:00
map_cgroup_storage.rst Remove duplicate words inside documentation 2022-09-27 13:21:43 -06:00
map_hash.rst bpf, docs: document BPF_MAP_TYPE_HASH and variants 2022-07-19 10:38:03 -07:00
map_lpm_trie.rst bpf: Replace bpf_lpm_trie_key 0-length array with flexible array 2024-08-29 17:30:22 +02:00
maps.rst bpf, docs: Move handling of maps to Documentation/bpf/maps.rst 2021-11-30 10:52:11 -08:00
other.rst bpf, docs: Fix ordering of bpf documentation 2021-11-17 23:24:01 +01:00
prog_cgroup_sockopt.rst bpf: Document optval > PAGE_SIZE behavior for sockopt hooks 2020-06-17 10:54:05 -07:00
prog_cgroup_sysctl.rst bpf: Document BPF_PROG_TYPE_CGROUP_SYSCTL 2019-04-18 16:05:36 -07:00
prog_flow_dissector.rst bpf/flow_dissector: add mode to enforce global BPF flow dissector 2019-10-07 20:16:33 -07:00
prog_lsm.rst bpf, docs: Rename bpf_lsm.rst to prog_lsm.rst 2021-11-17 23:23:58 +01:00
prog_sk_lookup.rst bpf: sk_lookup: Add user documentation 2020-08-24 14:46:50 -07:00
programs.rst bpf, docs: Fix ordering of bpf documentation 2021-11-17 23:24:01 +01:00
ringbuf.rst docs/bpf: Remove source code links 2020-09-14 18:46:54 -07:00
s390.rst bpf: Add s390 testing documentation 2019-10-30 16:25:31 +01:00
syscall_api.rst bpf, docs: Fix ordering of bpf documentation 2021-11-17 23:24:01 +01:00
test_debug.rst bpf, docs: Fix ordering of bpf documentation 2021-11-17 23:24:01 +01:00
verifier.rst bpf, docs: Add a missing colon in verifier.rst 2022-02-28 18:20:35 +01:00