netdev - [PATCH bpf-next 06/13] bpf: Enable read-write access to skb metadata with dynptr slice

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20250630-skb-metadata-thru-dynptr-v1-6-f17da13625d8@cloudflare.com>
Date: Mon, 30 Jun 2025 16:55:39 +0200
From: Jakub Sitnicki <jakub@...udflare.com>
To: bpf@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>, 
 Arthur Fabre <arthur@...hurfabre.com>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Jesper Dangaard Brouer <hawk@...nel.org>, 
 Jesse Brandeburg <jbrandeburg@...udflare.com>, 
 Joanne Koong <joannelkoong@...il.com>, 
 Lorenzo Bianconi <lorenzo@...nel.org>, 
 Toke Høiland-Jørgensen <thoiland@...hat.com>, 
 Yan Zhai <yan@...udflare.com>, netdev@...r.kernel.org, 
 kernel-team@...udflare.com, Stanislav Fomichev <sdf@...ichev.me>
Subject: [PATCH bpf-next 06/13] bpf: Enable read-write access to skb
 metadata with dynptr slice

Make it possible to read from or write to skb metadata area using the
dynptr slices creates with bpf_dynptr_slice() or bpf_dynptr_slice_rdwr().

This prepares ground for access to skb metadata from all BPF hooks
which operate on __sk_buff context.

Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
---
 net/core/filter.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index ab6599f42bb7..020da46f93a7 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -12033,9 +12033,14 @@ void *bpf_dynptr_skb_slice(const struct bpf_dynptr_kern *ptr, u32 offset,
 		else
 			return skb_pointer_if_linear(skb, offset, len);
 
-	case SKB_DYNPTR_METADATA:
-		return NULL;	/* not implemented */
+	case SKB_DYNPTR_METADATA: {
+		u32 meta_len = skb_metadata_len(skb);
 
+		if (len > meta_len || offset > meta_len - len)
+			return NULL; /* out of bounds */
+
+		return skb_metadata_end(skb) - meta_len + offset;
+	}
 	default:
 		WARN_ONCE(true, "%s: unknown skb dynptr offset %d\n", __func__, ptr->offset);
 		return NULL;

-- 
2.43.0