On 2/20/24 7:54 PM, 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.
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@xxxxxxx>
Closes: https://paste.debian.net/hidden/ca500597/
Acked-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
[...]
The build in BPF CI is still broken, did you try to build selftests?
https://github.com/kernel-patches/bpf/actions/runs/7978647641
[...]
GEN-SKEL [test_progs] linked_funcs.skel.h
LINK-BPF [test_progs] test_usdt.bpf.o
GEN-SKEL [test_progs-no_alu32] profiler1.skel.h
GEN-SKEL [test_progs] test_usdt.skel.h
In file included from /tmp/work/bpf/bpf/tools/include/uapi/linux/bpf.h:11,
from test_cpp.cpp:4:
/tmp/work/bpf/bpf/tools/include/uapi/linux/bpf.h:92:17: error: ‘struct bpf_lpm_trie_key_u8::<unnamed union>::bpf_lpm_trie_key_hdr’ invalid; an anonymous union may only have public non-static data members [-fpermissive]
92 | __struct_group(bpf_lpm_trie_key_hdr, hdr, /* no attrs */,
| ^~~~~~~~~~~~~~~~~~~~
/tmp/work/bpf/bpf/tools/include/uapi/linux/stddef.h:29:10: note: in definition of macro ‘__struct_group’
29 | struct TAG { MEMBERS } ATTRS NAME; \
| ^~~
BINARY bench
make: *** [Makefile:703: /tmp/work/bpf/bpf/tools/testing/selftests/bpf/test_cpp] Error 1
make: *** Waiting for unfinished jobs....
make: Leaving directory '/tmp/work/bpf/bpf/tools/testing/selftests/bpf'
Error: Process completed with exit code 2.
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 754e68ca8744..31e9bdd4641e 100644
--- a/include/uapi/linux/bpf.h
+++ b/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) */
