diff options
| author | Yonghong Song <yonghong.song@linux.dev> | 2023-08-22 08:00:53 +0300 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2023-08-22 19:43:55 +0300 |
| commit | ab6c637ad0276e42f8acabcbc64932a6d346dab3 (patch) | |
| tree | 949811202c1bf84feed08e2606739abfabd6db19 /kernel/bpf | |
| parent | d56518380085d78f179cdc701d791ace4acb1d23 (diff) | |
| download | linux-ab6c637ad0276e42f8acabcbc64932a6d346dab3.tar.xz | |
bpf: Fix a bpf_kptr_xchg() issue with local kptr
When reviewing local percpu kptr support, Alexei discovered a bug
wherea bpf_kptr_xchg() may succeed even if the map value kptr type and
locally allocated obj type do not match ([1]). Missed struct btf_id
comparison is the reason for the bug. This patch added such struct btf_id
comparison and will flag verification failure if types do not match.
[1] https://lore.kernel.org/bpf/20230819002907.io3iphmnuk43xblu@macbook-pro-8.dhcp.thefacebook.com/#t
Reported-by: Alexei Starovoitov <ast@kernel.org>
Fixes: 738c96d5e2e3 ("bpf: Allow local kptrs to be exchanged via bpf_kptr_xchg")
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20230822050053.2886960-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf')
| -rw-r--r-- | kernel/bpf/verifier.c | 25 |
1 files changed, 15 insertions, 10 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 4ccca1f6c998..3a91bfd7b9cc 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -4990,20 +4990,22 @@ static int map_kptr_match_type(struct bpf_verifier_env *env, struct bpf_reg_state *reg, u32 regno) { const char *targ_name = btf_type_name(kptr_field->kptr.btf, kptr_field->kptr.btf_id); - int perm_flags = PTR_MAYBE_NULL | PTR_TRUSTED | MEM_RCU; + int perm_flags; const char *reg_name = ""; - /* Only unreferenced case accepts untrusted pointers */ - if (kptr_field->type == BPF_KPTR_UNREF) - perm_flags |= PTR_UNTRUSTED; + if (btf_is_kernel(reg->btf)) { + perm_flags = PTR_MAYBE_NULL | PTR_TRUSTED | MEM_RCU; + + /* Only unreferenced case accepts untrusted pointers */ + if (kptr_field->type == BPF_KPTR_UNREF) + perm_flags |= PTR_UNTRUSTED; + } else { + perm_flags = PTR_MAYBE_NULL | MEM_ALLOC; + } if (base_type(reg->type) != PTR_TO_BTF_ID || (type_flag(reg->type) & ~perm_flags)) goto bad_type; - if (!btf_is_kernel(reg->btf)) { - verbose(env, "R%d must point to kernel BTF\n", regno); - return -EINVAL; - } /* We need to verify reg->type and reg->btf, before accessing reg->btf */ reg_name = btf_type_name(reg->btf, reg->btf_id); @@ -5016,7 +5018,7 @@ static int map_kptr_match_type(struct bpf_verifier_env *env, if (__check_ptr_off_reg(env, reg, regno, true)) return -EACCES; - /* A full type match is needed, as BTF can be vmlinux or module BTF, and + /* A full type match is needed, as BTF can be vmlinux, module or prog BTF, and * we also need to take into account the reg->off. * * We want to support cases like: @@ -7916,7 +7918,10 @@ found: verbose(env, "verifier internal error: unimplemented handling of MEM_ALLOC\n"); return -EFAULT; } - /* Handled by helper specific checks */ + if (meta->func_id == BPF_FUNC_kptr_xchg) { + if (map_kptr_match_type(env, meta->kptr_field, reg, regno)) + return -EACCES; + } break; case PTR_TO_BTF_ID | MEM_PERCPU: case PTR_TO_BTF_ID | MEM_PERCPU | PTR_TRUSTED: |