Commit 6877cd39 authored by Jakub Sitnicki's avatar Jakub Sitnicki Committed by Martin KaFai Lau
Browse files

bpf: Enable read/write access to skb metadata through a dynptr 



Now that we can create a dynptr to skb metadata, make reads to the metadata
area possible with bpf_dynptr_read() or through a bpf_dynptr_slice(), and
make writes to the metadata area possible with bpf_dynptr_write() or
through a bpf_dynptr_slice_rdwr().

Note that for cloned skbs which share data with the original, we limit the
skb metadata dynptr to be read-only since we don't unclone on a
bpf_dynptr_write to metadata.

Signed-off-by: default avatarJakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20250814-skb-metadata-thru-dynptr-v7-2-8a39e636e0fb@cloudflare.com
parent 89d912e4

include/linux/filter.h

+6 −0
Original line number Diff line number Diff line
@@ -1784,6 +1784,7 @@ 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);

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,

				       void *to, u32 len)
@@ -1818,6 +1819,11 @@ static inline void bpf_xdp_copy_buf(struct xdp_buff *xdp, unsigned long off, voi 
				    unsigned long len, bool flush)

{

}



static inline void *bpf_skb_meta_pointer(struct sk_buff *skb, u32 offset)

{

	return NULL;

}

#endif /* CONFIG_NET */



#endif /* __LINUX_FILTER_H__ */

kernel/bpf/helpers.c

+7 −3
Original line number Diff line number Diff line
@@ -1781,7 +1781,8 @@ static int __bpf_dynptr_read(void *dst, u32 len, const struct bpf_dynptr_kern *s 
	case BPF_DYNPTR_TYPE_XDP:

		return __bpf_xdp_load_bytes(src->data, src->offset + offset, dst, len);

	case BPF_DYNPTR_TYPE_SKB_META:

		return -EOPNOTSUPP; /* not implemented */

		memmove(dst, bpf_skb_meta_pointer(src->data, src->offset + offset), len);

		return 0;

	default:

		WARN_ONCE(true, "bpf_dynptr_read: unknown dynptr type %d\n", type);

		return -EFAULT;
@@ -1839,7 +1840,10 @@ 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 */

		if (flags)

			return -EINVAL;

		memmove(bpf_skb_meta_pointer(dst->data, dst->offset + offset), src, len);

		return 0;

	default:

		WARN_ONCE(true, "bpf_dynptr_write: unknown dynptr type %d\n", type);

		return -EFAULT;
@@ -2716,7 +2720,7 @@ __bpf_kfunc void *bpf_dynptr_slice(const struct bpf_dynptr *p, u32 offset, 
		return buffer__opt;

	}

	case BPF_DYNPTR_TYPE_SKB_META:

		return NULL; /* not implemented */

		return bpf_skb_meta_pointer(ptr->data, ptr->offset + offset);

	default:

		WARN_ONCE(true, "unknown dynptr type %d\n", type);

		return NULL;

net/core/filter.c

+16 −0
Original line number Diff line number Diff line
@@ -11990,6 +11990,16 @@ bpf_sk_base_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
	return func;

}



/**

 * bpf_skb_meta_pointer() - Gets a mutable pointer within the skb metadata area.

 * @skb: socket buffer carrying the metadata

 * @offset: offset into the metadata area, must be <= skb_metadata_len()

 */

void *bpf_skb_meta_pointer(struct sk_buff *skb, u32 offset)

{

	return skb_metadata_end(skb) - skb_metadata_len(skb) + offset;

}



__bpf_kfunc_start_defs();

__bpf_kfunc int bpf_dynptr_from_skb(struct __sk_buff *s, u64 flags,

				    struct bpf_dynptr *ptr__uninit)
@@ -12017,6 +12027,9 @@ __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
@@ -12034,6 +12047,9 @@ __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;

}