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Mon, 21 Jul 2025 03:53:25 -0700 (PDT) From: Jakub Sitnicki Date: Mon, 21 Jul 2025 12:52:41 +0200 Subject: [PATCH bpf-next v3 03/10] bpf: Enable write access to skb metadata with bpf_dynptr_write Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20250721-skb-metadata-thru-dynptr-v3-3-e92be5534174@cloudflare.com> References: <20250721-skb-metadata-thru-dynptr-v3-0-e92be5534174@cloudflare.com> In-Reply-To: <20250721-skb-metadata-thru-dynptr-v3-0-e92be5534174@cloudflare.com> To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Arthur Fabre , Daniel Borkmann , Eric Dumazet , Jakub Kicinski , Jesper Dangaard Brouer , Jesse Brandeburg , Joanne Koong , Lorenzo Bianconi , Martin KaFai Lau , =?utf-8?q?Toke_H=C3=B8iland-J=C3=B8rgensen?= , Yan Zhai , kernel-team@cloudflare.com, netdev@vger.kernel.org, Jakub Sitnicki , Stanislav Fomichev X-Mailer: b4 0.15-dev-07fe9 Make it possible to write to skb metadata area using the bpf_dynptr_write() BPF helper. This prepares ground for access to skb metadata from all BPF hooks which operate on __sk_buff context. Signed-off-by: Jakub Sitnicki --- include/linux/filter.h | 8 ++++++++ kernel/bpf/helpers.c | 2 +- net/core/filter.c | 12 ++++++++++++ 3 files changed, 21 insertions(+), 1 deletion(-) diff --git a/include/linux/filter.h b/include/linux/filter.h index de0d1ce34f0d..7709e30ce2bb 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -1774,6 +1774,8 @@ void bpf_xdp_copy_buf(struct xdp_buff *xdp, unsigned long off, void *buf, unsigned long len, bool flush); int bpf_skb_meta_load_bytes(const struct sk_buff *src, u32 offset, void *dst, u32 len); +int bpf_skb_meta_store_bytes(struct sk_buff *dst, u32 offset, + const void *src, u32 len); #else /* CONFIG_NET */ static inline int __bpf_skb_load_bytes(const struct sk_buff *skb, u32 offset, void *to, u32 len) @@ -1814,6 +1816,12 @@ static inline int bpf_skb_meta_load_bytes(const struct sk_buff *src, u32 offset, { return -EOPNOTSUPP; } + +static inline int bpf_skb_meta_store_bytes(struct sk_buff *dst, u32 offset, + const void *src, u32 len) +{ + return -EOPNOTSUPP; +} #endif /* CONFIG_NET */ #endif /* __LINUX_FILTER_H__ */ diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 34027a799679..ee057051db94 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -1839,7 +1839,7 @@ int __bpf_dynptr_write(const struct bpf_dynptr_kern *dst, u32 offset, void *src, return -EINVAL; return __bpf_xdp_store_bytes(dst->data, dst->offset + offset, src, len); case BPF_DYNPTR_TYPE_SKB_META: - return -EOPNOTSUPP; /* not implemented */ + return bpf_skb_meta_store_bytes(dst->data, dst->offset + offset, src, len); default: WARN_ONCE(true, "bpf_dynptr_write: unknown dynptr type %d\n", type); return -EFAULT; diff --git a/net/core/filter.c b/net/core/filter.c index 4b787c56b220..3cbadee77492 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -11990,6 +11990,18 @@ int bpf_skb_meta_load_bytes(const struct sk_buff *skb, u32 offset, return 0; } +int bpf_skb_meta_store_bytes(struct sk_buff *dst, u32 offset, + const void *src, u32 len) +{ + u32 meta_len = skb_metadata_len(dst); + + if (len > meta_len || offset > meta_len - len) + return -E2BIG; /* out of bounds */ + + memmove(skb_metadata_end(dst) - meta_len + offset, src, len); + return 0; +} + static int dynptr_from_skb_meta(struct __sk_buff *skb_, u64 flags, struct bpf_dynptr *ptr_, bool rdonly) { -- 2.43.0