[PATCH bpf-next v4 03/16] bpf: Unclone skb head on bpf_dynptr_write to skb metadata
From: Jakub Sitnicki <jakub@cloudflare.com>
Date: 2025-11-05 20:19:55
Also in:
bpf
Subsystem:
bpf [core], bpf [general] (safe dynamic programs and tools), bpf [networking] (tcx & tc bpf, sock_addr), networking [general], the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
Currently bpf_dynptr_from_skb_meta() marks the dynptr as read-only when the skb is cloned, preventing writes to metadata. Remove this restriction and unclone the skb head on bpf_dynptr_write() to metadata, now that the metadata is preserved during uncloning. This makes metadata dynptr consistent with skb dynptr, allowing writes regardless of whether the skb is cloned. Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com> --- include/linux/filter.h | 9 +++++++++ kernel/bpf/helpers.c | 6 ++---- net/core/filter.c | 18 ++++++++++++------ 3 files changed, 23 insertions(+), 10 deletions(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h
index f5c859b8131a..2ff4fc1c2386 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h@@ -1781,6 +1781,8 @@ int __bpf_xdp_store_bytes(struct xdp_buff *xdp, u32 offset, void *buf, u32 len); void *bpf_xdp_pointer(struct xdp_buff *xdp, u32 offset, u32 len); void bpf_xdp_copy_buf(struct xdp_buff *xdp, unsigned long off, void *buf, unsigned long len, bool flush); +int __bpf_skb_meta_store_bytes(struct sk_buff *skb, u32 offset, + const void *from, u32 len, u64 flags); void *bpf_skb_meta_pointer(struct sk_buff *skb, u32 offset); #else /* CONFIG_NET */ static inline int __bpf_skb_load_bytes(const struct sk_buff *skb, u32 offset,
@@ -1817,6 +1819,13 @@ static inline void bpf_xdp_copy_buf(struct xdp_buff *xdp, unsigned long off, voi { } +static inline int __bpf_skb_meta_store_bytes(struct sk_buff *skb, u32 offset, + const void *from, u32 len, + u64 flags) +{ + return -EOPNOTSUPP; +} + static inline void *bpf_skb_meta_pointer(struct sk_buff *skb, u32 offset) { return ERR_PTR(-EOPNOTSUPP);
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 865b0dae38d1..050783245c0f 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c@@ -1890,10 +1890,8 @@ int __bpf_dynptr_write(const struct bpf_dynptr_kern *dst, u64 offset, void *src, return -EINVAL; return __bpf_xdp_store_bytes(dst->data, dst->offset + offset, src, len); case BPF_DYNPTR_TYPE_SKB_META: - if (flags) - return -EINVAL; - memmove(bpf_skb_meta_pointer(dst->data, dst->offset + offset), src, len); - return 0; + return __bpf_skb_meta_store_bytes(dst->data, dst->offset + offset, src, + len, flags); 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 1efec0d70d78..96714eab9c91 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c@@ -12023,6 +12023,18 @@ void *bpf_skb_meta_pointer(struct sk_buff *skb, u32 offset) return skb_metadata_end(skb) - skb_metadata_len(skb) + offset; } +int __bpf_skb_meta_store_bytes(struct sk_buff *skb, u32 offset, + const void *from, u32 len, u64 flags) +{ + if (unlikely(flags)) + return -EINVAL; + if (unlikely(bpf_try_make_writable(skb, 0))) + return -EFAULT; + + memmove(bpf_skb_meta_pointer(skb, offset), from, len); + return 0; +} + __bpf_kfunc_start_defs(); __bpf_kfunc int bpf_dynptr_from_skb(struct __sk_buff *s, u64 flags, struct bpf_dynptr *ptr__uninit)
@@ -12050,9 +12062,6 @@ __bpf_kfunc int bpf_dynptr_from_skb(struct __sk_buff *s, u64 flags, * XDP context with bpf_xdp_adjust_meta(). Serves as an alternative to * &__sk_buff->data_meta. * - * If passed @skb_ is a clone which shares the data with the original, the - * dynptr will be read-only. This limitation may be lifted in the future. - * * Return: * * %0 - dynptr ready to use * * %-EINVAL - invalid flags, dynptr set to null
@@ -12070,9 +12079,6 @@ __bpf_kfunc int bpf_dynptr_from_skb_meta(struct __sk_buff *skb_, u64 flags, bpf_dynptr_init(ptr, skb, BPF_DYNPTR_TYPE_SKB_META, 0, skb_metadata_len(skb)); - if (skb_cloned(skb)) - bpf_dynptr_set_rdonly(ptr); - return 0; }
--
2.43.0