lkml.org 
[lkml]   [2024]   [Feb]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
SubjectRe: [PATCH v4] bpf: Replace bpf_lpm_trie_key 0-length array with flexible array
From
Date
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@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>
[...]

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) */

\
 
 \ /
  Last update: 2024-05-27 15:14    [W:0.044 / U:0.076 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site