[PATCH bpf-next 02/13] bpf: map_check_btf should fail if btf_parse_fields fails

[Dave Marchevsky <davemarchevsky@fb.com>]

map_check_btf calls btf_parse_fields to create a btf_record for its
value_type. If there are no special fields in the value_type
btf_parse_fields returns NULL, whereas if there special value_type
fields but they are invalid in some way an error is returned.

An example invalid state would be:

  struct node_data {
    struct bpf_rb_node node;
    int data;
  };

  private(A) struct bpf_spin_lock glock;
  private(A) struct bpf_list_head ghead __contains(node_data, node);

groot should be invalid as its __contains tag points to a field with
type != "bpf_list_node".

Before this patch, such a scenario would result in btf_parse_fields
returning an error ptr, subsequent !IS_ERR_OR_NULL check failing,
and btf_check_and_fixup_fields returning 0, which would then be
returned by map_check_btf.

After this patch's changes, -EINVAL would be returned by map_check_btf
and the map would correctly fail to load.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Fixes: aa3496accc41 ("bpf: Refactor kptr_off_tab into btf_record")
---
 kernel/bpf/syscall.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 35972afb6850..c3599a7902f0 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1007,7 +1007,10 @@ static int map_check_btf(struct bpf_map *map, const struct btf *btf,
 	map->record = btf_parse_fields(btf, value_type,
 				       BPF_SPIN_LOCK | BPF_TIMER | BPF_KPTR | BPF_LIST_HEAD,
 				       map->value_size);
-	if (!IS_ERR_OR_NULL(map->record)) {
+	if (IS_ERR(map->record))
+		return -EINVAL;
+
+	if (map->record) {
 		int i;
 
 		if (!bpf_capable()) {
-- 
2.30.2