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Thu, 24 Jul 2025 02:44:02 -0700 (PDT) From: Jakub Sitnicki To: Martin KaFai Lau Cc: Alexei Starovoitov , Andrii Nakryiko , Arthur Fabre , Daniel Borkmann , Eduard Zingerman , Eric Dumazet , Jakub Kicinski , Jesper Dangaard Brouer , Jesse Brandeburg , Joanne Koong , Lorenzo Bianconi , Toke =?utf-8?Q?H=C3=B8iland-J?= =?utf-8?Q?=C3=B8rgensen?= , Yan Zhai , kernel-team@cloudflare.com, netdev@vger.kernel.org, bpf@vger.kernel.org, Stanislav Fomichev Subject: Re: [PATCH bpf-next v4 2/8] bpf: Enable read/write access to skb metadata through a dynptr In-Reply-To: (Martin KaFai Lau's message of "Wed, 23 Jul 2025 17:02:11 -0700") References: <20250723-skb-metadata-thru-dynptr-v4-0-a0fed48bcd37@cloudflare.com> <20250723-skb-metadata-thru-dynptr-v4-2-a0fed48bcd37@cloudflare.com> Date: Thu, 24 Jul 2025 11:44:01 +0200 Message-ID: <87y0sdx6se.fsf@cloudflare.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Wed, Jul 23, 2025 at 05:02 PM -07, Martin KaFai Lau wrote: > On 7/23/25 10:36 AM, Jakub Sitnicki wrote: >> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c >> index 9552b32208c5..237fb5f9d625 100644 >> --- a/kernel/bpf/helpers.c >> +++ b/kernel/bpf/helpers.c >> @@ -1781,7 +1781,7 @@ 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 */ >> + return bpf_skb_meta_load_bytes(src->data, src->offset + offset, dst, len); >> default: >> WARN_ONCE(true, "bpf_dynptr_read: unknown dynptr type %d\n", type); >> return -EFAULT; >> @@ -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 */ > > It needs to check the flags here such that the flags can be used in the future: > > if (flags) > return -EINVAL; > Missed that. Thanks. > pw-bot: cr > >> + 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; >> @@ -2716,7 +2716,7 @@ __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, len); >> default: >> WARN_ONCE(true, "unknown dynptr type %d\n", type); >> return NULL; >> diff --git a/net/core/filter.c b/net/core/filter.c >> index 0755dfc0fc2f..cf095897d4c1 100644 >> --- a/net/core/filter.c >> +++ b/net/core/filter.c >> @@ -11978,6 +11978,45 @@ bpf_sk_base_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) >> return func; >> } >> +static void *skb_metadata_pointer(const struct sk_buff *skb, u32 off, u32 >> len) >> +{ >> + u32 meta_len = skb_metadata_len(skb); >> + >> + if (len > meta_len || off > meta_len - len) > > A nit. > > After reading it again, I think this is a duplicated check. The > bpf_dynptr_check_off_len() called in the kfunc should have already checked the > same condition. I took a better-safe-than-sorry approach. Can skb_metadata_len() change after the call to bpf_dynptr_from_skb_meta()? Today it can't, but what if we let TC BPF resize the metadata area in the future? But you're right. It's duplicated code for now and can be dropped. > >> + return ERR_PTR(-E2BIG); /* out of bounds */ >> + >> + return skb_metadata_end(skb) - meta_len + off; >> +} >> + >> +int bpf_skb_meta_load_bytes(const struct sk_buff *src, u32 off, void *dst, u32 len) > > Since it needs a respin, I have a few nit comments that will be useful for > reading filter.c. > > Change the "const struct sk_buff *src" to "const struct sk_buff *skb". It is how > other places are naming the arg in filter.c. No problem. I will unify it with: int __bpf_skb_load_bytes(const struct sk_buff *skb, u32 offset, void *to, u32 len); int __bpf_skb_store_bytes(struct sk_buff *skb, u32 offset, const void *from, u32 len, u64 flags); > >> +{ >> + const void *p = skb_metadata_pointer(src, off, len); > > Not sure if this variable is still needed if skb_metadata_pointer does not > return err ptr. > > If it is still needed, use "const void *ptr" instead of "const void *p". The > bpf_xdp_pointer and skb_header_pointer callers in filter.c also use that naming. > Will do. >> + >> + if (IS_ERR(p)) >> + return PTR_ERR(p); >> + >> + memmove(dst, p, len); >> + return 0; >> +} >> + >> +int bpf_skb_meta_store_bytes(struct sk_buff *dst, u32 off, const void *src, u32 len) >> +{ >> + void *p = skb_metadata_pointer(dst, off, len); > > Same for the "struct sk_buff *dst" and "void *p" in this function. > Will change. >> + >> + if (IS_ERR(p)) >> + return PTR_ERR(p); >> + >> + memmove(p, src, len); >> + return 0; >> +} Thanks for reviewing.