bpf: Add btf_struct_ids_match function
Adding btf_struct_ids_match function to check if given address provided
by BTF object + offset is also address of another nested BTF object.
This allows to pass an argument to helper, which is defined via parent
BTF object + offset, like for bpf_d_path (added in following changes):
SEC("fentry/filp_close")
int BPF_PROG(prog_close, struct file *file, void *id)
{
...
ret = bpf_d_path(&file->f_path, ...
The first bpf_d_path argument is hold by verifier as BTF file object
plus offset of f_path member.
The btf_struct_ids_match function will walk the struct file object and
check if there's nested struct path object on the given offset.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200825192124.710397-9-jolsa@kernel.org
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3874879..f003cee 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3995,16 +3995,21 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
goto err_type;
}
} else if (arg_type == ARG_PTR_TO_BTF_ID) {
+ bool ids_match = false;
+
expected_type = PTR_TO_BTF_ID;
if (type != expected_type)
goto err_type;
if (!fn->check_btf_id) {
if (reg->btf_id != meta->btf_id) {
- verbose(env, "Helper has type %s got %s in R%d\n",
- kernel_type_name(meta->btf_id),
- kernel_type_name(reg->btf_id), regno);
-
- return -EACCES;
+ ids_match = btf_struct_ids_match(&env->log, reg->off, reg->btf_id,
+ meta->btf_id);
+ if (!ids_match) {
+ verbose(env, "Helper has type %s got %s in R%d\n",
+ kernel_type_name(meta->btf_id),
+ kernel_type_name(reg->btf_id), regno);
+ return -EACCES;
+ }
}
} else if (!fn->check_btf_id(reg->btf_id, arg)) {
verbose(env, "Helper does not support %s in R%d\n",
@@ -4012,7 +4017,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
return -EACCES;
}
- if (!tnum_is_const(reg->var_off) || reg->var_off.value || reg->off) {
+ if ((reg->off && !ids_match) || !tnum_is_const(reg->var_off) || reg->var_off.value) {
verbose(env, "R%d is a pointer to in-kernel struct with non-zero offset\n",
regno);
return -EACCES;
