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bpf: Refactor NULL-ness check in check_reg_type(). 

check_reg_type() unconditionally disallows PTR_TO_BTF_ID | PTR_MAYBE_NULL.
It's problematic for helpers that allow ARG_PTR_TO_BTF_ID_OR_NULL like
bpf_sk_storage_get(). Allow passing PTR_TO_BTF_ID | PTR_MAYBE_NULL into such
helpers. That technically includes bpf_kptr_xchg() helper, but in practice:
  bpf_kptr_xchg(..., bpf_cpumask_create());
is still disallowed because bpf_cpumask_create() returns ref counted pointer
with ref_obj_id > 0.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20230404045029.82870-6-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2023-04-03 21:50:26 -07:00 committed by Andrii Nakryiko
parent 91571a515d
commit add68b843f
1 changed files with 8 additions and 4 deletions
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12
kernel/bpf/verifier.c
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@ -7168,6 +7168,8 @@ found:
case PTR_TO_BTF_ID:
case PTR_TO_BTF_ID | PTR_TRUSTED:
case PTR_TO_BTF_ID | MEM_RCU:
case PTR_TO_BTF_ID | PTR_MAYBE_NULL:
case PTR_TO_BTF_ID | PTR_MAYBE_NULL | MEM_RCU:
{
/* For bpf_sk_release, it needs to match against first member
* 'struct sock_common', hence make an exception for it. This
@ -7176,6 +7178,12 @@ found:
bool strict_type_match = arg_type_is_release(arg_type) &&
meta->func_id != BPF_FUNC_sk_release;
if (type_may_be_null(reg->type) &&
(!type_may_be_null(arg_type) || arg_type_is_release(arg_type))) {
verbose(env, "Possibly NULL pointer passed to helper arg%d\n", regno);
return -EACCES;
}
if (!arg_btf_id) {
if (!compatible->btf_id) {
verbose(env, "verifier internal error: missing arg compatible BTF ID\n");
@ -7206,10 +7214,6 @@ found:
}
break;
}
case PTR_TO_BTF_ID | PTR_MAYBE_NULL:
case PTR_TO_BTF_ID | PTR_MAYBE_NULL | MEM_RCU:
verbose(env, "Possibly NULL pointer passed to helper arg%d\n", regno);
return -EACCES;
case PTR_TO_BTF_ID | MEM_ALLOC:
if (meta->func_id != BPF_FUNC_spin_lock && meta->func_id != BPF_FUNC_spin_unlock &&
meta->func_id != BPF_FUNC_kptr_xchg) {