[PATCH] bpf: Annotate struct bpf_cand_cache with __counted_by()

[Thorsten Blum]

Add the __counted_by compiler attribute to the flexible array member
cands to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.

Increment cnt before adding a new struct to the cands array.

Signed-off-by: Thorsten Blum <thorsten.blum@xxxxxxxxxx>
---
 kernel/bpf/btf.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 520f49f422fe..42bc70a56fcd 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7240,7 +7240,7 @@ struct bpf_cand_cache {
 	struct {
 		const struct btf *btf;
 		u32 id;
-	} cands[];
+	} cands[] __counted_by(cnt);
 };
 
 static DEFINE_MUTEX(cand_cache_mutex);
@@ -8784,9 +8784,9 @@ bpf_core_add_cands(struct bpf_cand_cache *cands, const struct btf *targ_btf,
 		memcpy(new_cands, cands, sizeof_cands(cands->cnt));
 		bpf_free_cands(cands);
 		cands = new_cands;
-		cands->cands[cands->cnt].btf = targ_btf;
-		cands->cands[cands->cnt].id = i;
 		cands->cnt++;
+		cands->cands[cands->cnt - 1].btf = targ_btf;
+		cands->cands[cands->cnt - 1].id = i;
 	}
 	return cands;
 }
-- 
2.46.0