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 [*]'
This includes fixing the selftest which was incorrectly using a
variable length struct as a header, identified earlier[1]. Avoid this
by just explicitly including the prefixlen member instead of struct
bpf_lpm_trie_key.
Note that it is not possible to simply remove the "data" member, as it
is referenced by userspace
cilium:
struct egress_gw_policy_key in_key = {
.lpm_key = { 32 + 24, {} },
.saddr = CLIENT_IP,
.daddr = EXTERNAL_SVC_IP & 0Xffffff,
};
systemd:
ipv6_map_fd = bpf_map_new(
BPF_MAP_TYPE_LPM_TRIE,
offsetof(struct bpf_lpm_trie_key, data) + sizeof(uint32_t)*4,
sizeof(uint64_t),
...
The only risk to UAPI would be if sizeof() were used directly on the
data member, which it does not seem to be. It is only used as a static
initializer destination and to find its location via offsetof().
Link: https://lore.kernel.org/all/202206281009.4332AA33@keescook/ [1]
Reported-by: Mark Rutland <[email protected]>
Closes: https://paste.debian.net/hidden/ca500597/
Signed-off-by: Kees Cook <[email protected]>
---
Cc: Alexei Starovoitov <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Yonghong Song <[email protected]>
Cc: John Fastabend <[email protected]>
Cc: KP Singh <[email protected]>
Cc: Stanislav Fomichev <[email protected]>
Cc: Hao Luo <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Mykola Lysenko <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Haowen Bai <[email protected]>
Cc: [email protected]
Cc: [email protected]
v2- clarify commit log, add more failure examples
v1- https://lore.kernel.org/all/[email protected]/
---
include/uapi/linux/bpf.h | 2 +-
tools/testing/selftests/bpf/progs/map_ptr_kern.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 754e68ca8744..359dd8a429c1 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -80,7 +80,7 @@ struct bpf_insn {
/* Key of an a BPF_MAP_TYPE_LPM_TRIE entry */
struct bpf_lpm_trie_key {
__u32 prefixlen; /* up to 32 for AF_INET, 128 for AF_INET6 */
- __u8 data[0]; /* Arbitrary size */
+ __u8 data[]; /* Arbitrary size */
};
struct bpf_cgroup_storage_key {
diff --git a/tools/testing/selftests/bpf/progs/map_ptr_kern.c b/tools/testing/selftests/bpf/progs/map_ptr_kern.c
index 3325da17ec81..1d476c6ae284 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;
+ __u32 prefixlen;
__u32 data;
};
--
2.34.1
On 2/16/24 17:55, 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 [*]'
>
> This includes fixing the selftest which was incorrectly using a
> variable length struct as a header, identified earlier[1]. Avoid this
> by just explicitly including the prefixlen member instead of struct
> bpf_lpm_trie_key.
>
> Note that it is not possible to simply remove the "data" member, as it
> is referenced by userspace
>
> cilium:
> struct egress_gw_policy_key in_key = {
> .lpm_key = { 32 + 24, {} },
> .saddr = CLIENT_IP,
> .daddr = EXTERNAL_SVC_IP & 0Xffffff,
> };
>
> systemd:
> ipv6_map_fd = bpf_map_new(
> BPF_MAP_TYPE_LPM_TRIE,
> offsetof(struct bpf_lpm_trie_key, data) + sizeof(uint32_t)*4,
> sizeof(uint64_t),
> ...
>
> The only risk to UAPI would be if sizeof() were used directly on the
> data member, which it does not seem to be. It is only used as a static
> initializer destination and to find its location via offsetof().
>
> Link: https://lore.kernel.org/all/202206281009.4332AA33@keescook/ [1]
> Reported-by: Mark Rutland <[email protected]>
> Closes: https://paste.debian.net/hidden/ca500597/
mmh... this URL expires: 2024-05-15
> Signed-off-by: Kees Cook <[email protected]>
Acked-by: Gustavo A. R. Silva <[email protected]>
Thanks!
--
Gustavo
> ---
> Cc: Alexei Starovoitov <[email protected]>
> Cc: Daniel Borkmann <[email protected]>
> Cc: Andrii Nakryiko <[email protected]>
> Cc: Martin KaFai Lau <[email protected]>
> Cc: Song Liu <[email protected]>
> Cc: Yonghong Song <[email protected]>
> Cc: John Fastabend <[email protected]>
> Cc: KP Singh <[email protected]>
> Cc: Stanislav Fomichev <[email protected]>
> Cc: Hao Luo <[email protected]>
> Cc: Jiri Olsa <[email protected]>
> Cc: Mykola Lysenko <[email protected]>
> Cc: Shuah Khan <[email protected]>
> Cc: Haowen Bai <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
>
> v2- clarify commit log, add more failure examples
> v1- https://lore.kernel.org/all/[email protected]/
> ---
> include/uapi/linux/bpf.h | 2 +-
> tools/testing/selftests/bpf/progs/map_ptr_kern.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 754e68ca8744..359dd8a429c1 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -80,7 +80,7 @@ struct bpf_insn {
> /* Key of an a BPF_MAP_TYPE_LPM_TRIE entry */
> struct bpf_lpm_trie_key {
> __u32 prefixlen; /* up to 32 for AF_INET, 128 for AF_INET6 */
> - __u8 data[0]; /* Arbitrary size */
> + __u8 data[]; /* Arbitrary size */
> };
>
> struct bpf_cgroup_storage_key {
> diff --git a/tools/testing/selftests/bpf/progs/map_ptr_kern.c b/tools/testing/selftests/bpf/progs/map_ptr_kern.c
> index 3325da17ec81..1d476c6ae284 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;
> + __u32 prefixlen;
> __u32 data;
> };
>
On Fri, Feb 16, 2024 at 06:27:08PM -0600, Gustavo A. R. Silva wrote:
>
>
> On 2/16/24 17:55, 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 [*]'
> >
> > This includes fixing the selftest which was incorrectly using a
> > variable length struct as a header, identified earlier[1]. Avoid this
> > by just explicitly including the prefixlen member instead of struct
> > bpf_lpm_trie_key.
> >
> > Note that it is not possible to simply remove the "data" member, as it
> > is referenced by userspace
> >
> > cilium:
> > struct egress_gw_policy_key in_key = {
> > .lpm_key = { 32 + 24, {} },
> > .saddr = CLIENT_IP,
> > .daddr = EXTERNAL_SVC_IP & 0Xffffff,
> > };
> >
> > systemd:
> > ipv6_map_fd = bpf_map_new(
> > BPF_MAP_TYPE_LPM_TRIE,
> > offsetof(struct bpf_lpm_trie_key, data) + sizeof(uint32_t)*4,
> > sizeof(uint64_t),
> > ...
> >
> > The only risk to UAPI would be if sizeof() were used directly on the
> > data member, which it does not seem to be. It is only used as a static
> > initializer destination and to find its location via offsetof().
> >
> > Link: https://lore.kernel.org/all/202206281009.4332AA33@keescook/ [1]
> > Reported-by: Mark Rutland <[email protected]>
> > Closes: https://paste.debian.net/hidden/ca500597/
>
> mmh... this URL expires: 2024-05-15
Yup, but that's why I included the run-time splat above too. :)
--
Kees Cook
On 2/17/24 4:03 AM, Kees Cook wrote:
> On Fri, Feb 16, 2024 at 06:27:08PM -0600, Gustavo A. R. Silva wrote:
>> On 2/16/24 17:55, 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 [*]'
>>>
>>> This includes fixing the selftest which was incorrectly using a
>>> variable length struct as a header, identified earlier[1]. Avoid this
>>> by just explicitly including the prefixlen member instead of struct
>>> bpf_lpm_trie_key.
>>>
>>> Note that it is not possible to simply remove the "data" member, as it
>>> is referenced by userspace
>>>
>>> cilium:
>>> struct egress_gw_policy_key in_key = {
>>> .lpm_key = { 32 + 24, {} },
>>> .saddr = CLIENT_IP,
>>> .daddr = EXTERNAL_SVC_IP & 0Xffffff,
>>> };
>>>
>>> systemd:
>>> ipv6_map_fd = bpf_map_new(
>>> BPF_MAP_TYPE_LPM_TRIE,
>>> offsetof(struct bpf_lpm_trie_key, data) + sizeof(uint32_t)*4,
>>> sizeof(uint64_t),
>>> ...
>>>
>>> The only risk to UAPI would be if sizeof() were used directly on the
>>> data member, which it does not seem to be. It is only used as a static
>>> initializer destination and to find its location via offsetof().
>>>
>>> Link: https://lore.kernel.org/all/202206281009.4332AA33@keescook/ [1]
>>> Reported-by: Mark Rutland <[email protected]>
>>> Closes: https://paste.debian.net/hidden/ca500597/
>>
>> mmh... this URL expires: 2024-05-15
>
> Yup, but that's why I included the run-time splat above too. :)
I don't quite follow, this basically undoes 3024d95a4c52 ("bpf: Partially revert
flexible-array member replacement") again with the small change that this 'fixes'
up the BPF selftest to not embed struct bpf_lpm_trie_key.
Outside of BPF selftests though aren't we readding the same error that we fixed
earlier for BPF programs in the wild which embed struct bpf_lpm_trie_key into their
key structure?
Thanks,
Daniel
On Mon, Feb 19, 2024 at 06:48:41PM +0100, Daniel Borkmann wrote:
> On 2/17/24 4:03 AM, Kees Cook wrote:
> > On Fri, Feb 16, 2024 at 06:27:08PM -0600, Gustavo A. R. Silva wrote:
> > > On 2/16/24 17:55, 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 [*]'
> > > >
> > > > This includes fixing the selftest which was incorrectly using a
> > > > variable length struct as a header, identified earlier[1]. Avoid this
> > > > by just explicitly including the prefixlen member instead of struct
> > > > bpf_lpm_trie_key.
> > > >
> > > > Note that it is not possible to simply remove the "data" member, as it
> > > > is referenced by userspace
> > > >
> > > > cilium:
> > > > struct egress_gw_policy_key in_key = {
> > > > .lpm_key = { 32 + 24, {} },
> > > > .saddr = CLIENT_IP,
> > > > .daddr = EXTERNAL_SVC_IP & 0Xffffff,
> > > > };
> > > >
> > > > systemd:
> > > > ipv6_map_fd = bpf_map_new(
> > > > BPF_MAP_TYPE_LPM_TRIE,
> > > > offsetof(struct bpf_lpm_trie_key, data) + sizeof(uint32_t)*4,
> > > > sizeof(uint64_t),
> > > > ...
> > > >
> > > > The only risk to UAPI would be if sizeof() were used directly on the
> > > > data member, which it does not seem to be. It is only used as a static
> > > > initializer destination and to find its location via offsetof().
> > > >
> > > > Link: https://lore.kernel.org/all/202206281009.4332AA33@keescook/ [1]
> > > > Reported-by: Mark Rutland <[email protected]>
> > > > Closes: https://paste.debian.net/hidden/ca500597/
> > >
> > > mmh... this URL expires: 2024-05-15
> >
> > Yup, but that's why I included the run-time splat above too. :)
>
> I don't quite follow, this basically undoes 3024d95a4c52 ("bpf: Partially revert
> flexible-array member replacement") again with the small change that this 'fixes'
> up the BPF selftest to not embed struct bpf_lpm_trie_key.
>
> Outside of BPF selftests though aren't we readding the same error that we fixed
> earlier for BPF programs in the wild which embed struct bpf_lpm_trie_key into their
> key structure?
Oops, yes, sorry. I see how that cilium does include it in the same
fashion. I will adjust this patch again. Thanks for double-checking!
struct egress_gw_policy_key {
struct bpf_lpm_trie_key lpm_key;
__u32 saddr;
__u32 daddr;
};
--
Kees Cook