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bpf: Unclone skb head on bpf_dynptr_write to skb metadata 

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>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20251105-skb-meta-rx-path-v4-3-5ceb08a9b37b@cloudflare.com
This commit is contained in:
Jakub Sitnicki 2025-11-05 21:19:40 +01:00 committed by Martin KaFai Lau
parent 290fc0be09
commit f38499ff45
3 changed files with 23 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
include/linux/filter.h
View File

@ -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);

6
kernel/bpf/helpers.c
View File

@ -1842,10 +1842,8 @@ 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:
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;

18
net/core/filter.c
View File

@ -12102,6 +12102,18 @@ 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)
@ -12129,9 +12141,6 @@ __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
@ -12149,9 +12158,6 @@ __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;
}