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bpf: Fix an error around PTR_UNTRUSTED

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Per discussion with Alexei, the PTR_UNTRUSTED flag should not been
cleared when we start to walk a new struct, because the struct in
question may be a struct nested in a union. We should also check and set
this flag before we walk its each member, in case itself is a union.
We will clear this flag if the field is BTF_TYPE_SAFE_RCU_OR_NULL.

Fixes: 6fcd486b3a ("bpf: Refactor RCU enforcement in the verifier.")
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/r/20230713025642.27477-2-laoar.shao@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Yafang Shao 2023-07-13 02:56:39 +00:00 committed by Alexei Starovoitov
parent f892cac237
commit 7ce4dc3e4a
2 changed files with 14 additions and 11 deletions
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20
kernel/bpf/btf.c
View File

@ -6133,7 +6133,6 @@ static int btf_struct_walk(struct bpf_verifier_log *log, const struct btf *btf,
const char *tname, *mname, *tag_value;
u32 vlen, elem_id, mid;
*flag = 0;
again:
if (btf_type_is_modifier(t))
t = btf_type_skip_modifiers(btf, t->type, NULL);
@ -6144,6 +6143,14 @@ again:
}
vlen = btf_type_vlen(t);
if (BTF_INFO_KIND(t->info) == BTF_KIND_UNION && vlen != 1 && !(*flag & PTR_UNTRUSTED))
/*
* walking unions yields untrusted pointers
* with exception of __bpf_md_ptr and other
* unions with a single member
*/
*flag |= PTR_UNTRUSTED;
if (off + size > t->size) {
/* If the last element is a variable size array, we may
* need to relax the rule.
@ -6304,15 +6311,6 @@ error:
* of this field or inside of this struct
*/
if (btf_type_is_struct(mtype)) {
if (BTF_INFO_KIND(mtype->info) == BTF_KIND_UNION &&
btf_type_vlen(mtype) != 1)
/*
* walking unions yields untrusted pointers
* with exception of __bpf_md_ptr and other
* unions with a single member
*/
*flag |= PTR_UNTRUSTED;
/* our field must be inside that union or struct */
t = mtype;
@ -6478,7 +6476,7 @@ bool btf_struct_ids_match(struct bpf_verifier_log *log,
bool strict)
{
const struct btf_type *type;
enum bpf_type_flag flag;
enum bpf_type_flag flag = 0;
int err;
/* Are we already done? */

5
kernel/bpf/verifier.c
View File

@ -6067,6 +6067,11 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env,
type_is_rcu_or_null(env, reg, field_name, btf_id)) {
/* __rcu tagged pointers can be NULL */
flag |= MEM_RCU | PTR_MAYBE_NULL;
/* We always trust them */
if (type_is_rcu_or_null(env, reg, field_name, btf_id) &&
flag & PTR_UNTRUSTED)
flag &= ~PTR_UNTRUSTED;
} else if (flag & (MEM_PERCPU | MEM_USER)) {
/* keep as-is */
} else {