On Tue, Jul 26, 2022 at 11:47:04AM -0700, Joanne Koong wrote:
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 59a217ca2dfd..0730cd198a7f 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5241,11 +5241,22 @@ union bpf_attr {
> * Description
> * Write *len* bytes from *src* into *dst*, starting from *offset*
> * into *dst*.
> - * *flags* is currently unused.
> + *
> + * *flags* must be 0 except for skb-type dynptrs.
> + *
> + * For skb-type dynptrs:
> + * * if *offset* + *len* extends into the skb's paged buffers, the user
> + * should manually pull the skb with bpf_skb_pull and then try again.
bpf_skb_pull_data().
Probably need formatting like, **bpf_skb_pull_data**\ ()
> + *
> + * * *flags* are a combination of **BPF_F_RECOMPUTE_CSUM** (automatically
> + * recompute the checksum for the packet after storing the bytes) and
> + * **BPF_F_INVALIDATE_HASH** (set *skb*\ **->hash**, *skb*\
> + * **->swhash** and *skb*\ **->l4hash** to 0).
> * Return
> * 0 on success, -E2BIG if *offset* + *len* exceeds the length
> * of *dst*'s data, -EINVAL if *dst* is an invalid dynptr or if *dst*
> - * is a read-only dynptr or if *flags* is not 0.
> + * is a read-only dynptr or if *flags* is not correct, -EAGAIN if for
> + * skb-type dynptrs the write extends into the skb's paged buffers.
May also mention other negative errors is similar to the bpf_skb_store_bytes()
instead of mentioning them one-by-one here.
> *
> * void *bpf_dynptr_data(struct bpf_dynptr *ptr, u32 offset, u32 len)
> * Description
> @@ -5253,10 +5264,19 @@ union bpf_attr {
> *
> * *len* must be a statically known value. The returned data slice
> * is invalidated whenever the dynptr is invalidated.
> + *
> + * For skb-type dynptrs:
> + * * if *offset* + *len* extends into the skb's paged buffers,
> + * the user should manually pull the skb with bpf_skb_pull and then
same here. bpf_skb_pull_data().
> + * try again.
> + *
> + * * the data slice is automatically invalidated anytime a
> + * helper call that changes the underlying packet buffer
> + * (eg bpf_skb_pull) is called.
> * Return
> * Pointer to the underlying dynptr data, NULL if the dynptr is
> * read-only, if the dynptr is invalid, or if the offset and length
> - * is out of bounds.
> + * is out of bounds or in a paged buffer for skb-type dynptrs.
> *
> * s64 bpf_tcp_raw_gen_syncookie_ipv4(struct iphdr *iph, struct tcphdr *th, u32 th_len)
> * Description
> @@ -5331,6 +5351,21 @@ union bpf_attr {
> * **-EACCES** if the SYN cookie is not valid.
> *
> * **-EPROTONOSUPPORT** if CONFIG_IPV6 is not builtin.
> + *
> + * long bpf_dynptr_from_skb(struct sk_buff *skb, u64 flags, struct bpf_dynptr *ptr)
> + * Description
> + * Get a dynptr to the data in *skb*. *skb* must be the BPF program
> + * context. Depending on program type, the dynptr may be read-only,
> + * in which case trying to obtain a direct data slice to it through
> + * bpf_dynptr_data will return an error.
> + *
> + * Calls that change the *skb*'s underlying packet buffer
> + * (eg bpf_skb_pull_data) do not invalidate the dynptr, but they do
> + * invalidate any data slices associated with the dynptr.
> + *
> + * *flags* is currently unused, it must be 0 for now.
> + * Return
> + * 0 on success or -EINVAL if flags is not 0.
> */
[ ... ]
> @@ -1528,15 +1544,38 @@ static const struct bpf_func_proto bpf_dynptr_read_proto = {
> BPF_CALL_5(bpf_dynptr_write, struct bpf_dynptr_kern *, dst, u32, offset, void *, src,
> u32, len, u64, flags)
> {
> + enum bpf_dynptr_type type;
> int err;
>
> - if (!dst->data || flags || bpf_dynptr_is_rdonly(dst))
> + if (!dst->data || bpf_dynptr_is_rdonly(dst))
> return -EINVAL;
>
> err = bpf_dynptr_check_off_len(dst, offset, len);
> if (err)
> return err;
>
> + type = bpf_dynptr_get_type(dst);
> +
> + if (flags) {
> + if (type == BPF_DYNPTR_TYPE_SKB) {
> + if (flags & ~(BPF_F_RECOMPUTE_CSUM | BPF_F_INVALIDATE_HASH))
nit. The flags is the same as __bpf_skb_store_bytes(). __bpf_skb_store_bytes()
can reject as well instead of duplicating the test here.
> + return -EINVAL;
> + } else {
> + return -EINVAL;
> + }
> + }
> +
> + if (type == BPF_DYNPTR_TYPE_SKB) {
> + struct sk_buff *skb = dst->data;
> +
> + /* if the data is paged, the caller needs to pull it first */
> + if (dst->offset + offset + len > skb->len - skb->data_len)
> + return -EAGAIN;
> +
> + return __bpf_skb_store_bytes(skb, dst->offset + offset, src, len,
> + flags);
> + }
> +
