When trying to finish resolving a struct member, btf_struct_resolve
saves the member type id in a u16 temporary variable. This truncates
the 32 bit type id value if it exceeds UINT16_MAX.
As a result, structs that have members with type ids > UINT16_MAX and
which need resolution will fail with a message like this:
[67414] STRUCT ff_device size=120 vlen=12
effect_owners type_id=67434 bits_offset=960 Member exceeds struct_size
Fix this by changing the type of last_member_type_id to u32.
Fixes: eb3f595dab40 ("bpf: btf: Validate type reference")
Signed-off-by: Lorenz Bauer <[email protected]>
---
kernel/bpf/btf.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 7e64447659f3..36fd4b509294 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3128,7 +3128,7 @@ static int btf_struct_resolve(struct btf_verifier_env *env,
if (v->next_member) {
const struct btf_type *last_member_type;
const struct btf_member *last_member;
- u16 last_member_type_id;
+ u32 last_member_type_id;
last_member = btf_type_member(v->t) + v->next_member - 1;
last_member_type_id = last_member->type;
--
2.34.1
On 09/09, Lorenz Bauer wrote:
> When trying to finish resolving a struct member, btf_struct_resolve
> saves the member type id in a u16 temporary variable. This truncates
> the 32 bit type id value if it exceeds UINT16_MAX.
> As a result, structs that have members with type ids > UINT16_MAX and
> which need resolution will fail with a message like this:
> [67414] STRUCT ff_device size=120 vlen=12
> effect_owners type_id=67434 bits_offset=960 Member exceeds
> struct_size
> Fix this by changing the type of last_member_type_id to u32.
Makes sense to me; I'm surprised the compiler isn't raising a warning on
line:
last_member_type_id = last_member->type;
Reviewed-by: Stanislav Fomichev <[email protected]>
> Fixes: eb3f595dab40 ("bpf: btf: Validate type reference")
> Signed-off-by: Lorenz Bauer <[email protected]>
> ---
> kernel/bpf/btf.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 7e64447659f3..36fd4b509294 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -3128,7 +3128,7 @@ static int btf_struct_resolve(struct
> btf_verifier_env *env,
> if (v->next_member) {
> const struct btf_type *last_member_type;
> const struct btf_member *last_member;
> - u16 last_member_type_id;
> + u32 last_member_type_id;
> last_member = btf_type_member(v->t) + v->next_member - 1;
> last_member_type_id = last_member->type;
> --
> 2.34.1
On 9/9/22 2:21 AM, Lorenz Bauer wrote:
> When trying to finish resolving a struct member, btf_struct_resolve
> saves the member type id in a u16 temporary variable. This truncates
> the 32 bit type id value if it exceeds UINT16_MAX.
>
> As a result, structs that have members with type ids > UINT16_MAX and
> which need resolution will fail with a message like this:
>
> [67414] STRUCT ff_device size=120 vlen=12
> effect_owners type_id=67434 bits_offset=960 Member exceeds struct_size
>
> Fix this by changing the type of last_member_type_id to u32.
>
> Fixes: eb3f595dab40 ("bpf: btf: Validate type reference")
The fix tag should be
Fixes: a0791f0df7d2 ("bpf: fix BTF limits")
> Signed-off-by: Lorenz Bauer <[email protected]>
> ---
> kernel/bpf/btf.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 7e64447659f3..36fd4b509294 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -3128,7 +3128,7 @@ static int btf_struct_resolve(struct btf_verifier_env *env,
> if (v->next_member) {
> const struct btf_type *last_member_type;
> const struct btf_member *last_member;
> - u16 last_member_type_id;
> + u32 last_member_type_id;
The change makes sense.
The kernel's vmlinux and module btf parsing doesn't go through this
resolve check though. Are you trying to __sys_bpf(BPF_BTF_LOAD) the btf
from the vmlinux file into the kernel ?
On Fri, 9 Sep 2022, at 19:17, Martin KaFai Lau wrote:
>
> The fix tag should be
>
> Fixes: a0791f0df7d2 ("bpf: fix BTF limits")
Ah, thanks very much! Sent a v2.
> The change makes sense.
>
> The kernel's vmlinux and module btf parsing doesn't go through this
> resolve check though. Are you trying to __sys_bpf(BPF_BTF_LOAD) the btf
> from the vmlinux file into the kernel ?
Yes, with the twist that the BTF was serialised by github.com/cilium/ebpf instead of libbpf.