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.
Fixes: 6fcd486b3a0a ("bpf: Refactor RCU enforcement in the verifier.")
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
kernel/bpf/btf.c | 20 +++++++++-----------
1 file changed, 9 insertions(+), 11 deletions(-)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 29fe21099298..e0a493230727 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -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:
tname = __btf_name_by_offset(btf, t->name_off);
if (!btf_type_is_struct(t)) {
@@ -6142,6 +6141,14 @@ static int btf_struct_walk(struct bpf_verifier_log *log, const struct btf *btf,
}
vlen = btf_type_vlen(t);
+ if (BTF_INFO_KIND(t->info) == BTF_KIND_UNION && vlen != 1)
+ /*
+ * 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.
@@ -6302,15 +6309,6 @@ static int btf_struct_walk(struct bpf_verifier_log *log, const struct btf *btf,
* 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;
@@ -6476,7 +6474,7 @@ 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? */
--
2.39.3
