linux-hardening - [PATCH] bpf: Annotate struct bpf_cand_cache with __counted

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Message-ID: <20240813151752.95161-2-thorsten.blum@toblux.com>
Date: Tue, 13 Aug 2024 17:17:53 +0200
From: Thorsten Blum <thorsten.blum@...lux.com>
To: martin.lau@...ux.dev,
	ast@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org,
	eddyz87@...il.com,
	song@...nel.org,
	yonghong.song@...ux.dev,
	john.fastabend@...il.com,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com,
	jolsa@...nel.org,
	kees@...nel.org,
	gustavoars@...nel.org
Cc: bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org,
	Thorsten Blum <thorsten.blum@...lux.com>
Subject: [PATCH] bpf: Annotate struct bpf_cand_cache with __counted_by()

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@...lux.com>
---
 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