On Mon, Jun 30, 2025 at 09:27 AM -07, Stanislav Fomichev wrote:
> On 06/30, Jakub Sitnicki wrote:
>> Add a new flag for the bpf_dynptr_from_skb helper to let users to create
>> dynptrs to skb metadata area. Access paths are stubbed out. Implemented by
>> the following changes.
>>
>> Signed-off-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
>> ---
>> include/uapi/linux/bpf.h | 9 ++++++++
>> net/core/filter.c | 60 +++++++++++++++++++++++++++++++++++++++++-------
>> 2 files changed, 61 insertions(+), 8 deletions(-)
>>
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index 719ba230032f..ab5730d2fb29 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -7591,4 +7591,13 @@ enum bpf_kfunc_flags {
>> BPF_F_PAD_ZEROS = (1ULL << 0),
>> };
>>
>> +/**
>> + * enum bpf_dynptr_from_skb_flags - Flags for bpf_dynptr_from_skb()
>> + *
>> + * @BPF_DYNPTR_F_SKB_METADATA: Create dynptr to the SKB metadata area
>> + */
>> +enum bpf_dynptr_from_skb_flags {
>> + BPF_DYNPTR_F_SKB_METADATA = (1ULL << 0),
>> +};
>> +
>> #endif /* _UAPI__LINUX_BPF_H__ */
>> diff --git a/net/core/filter.c b/net/core/filter.c
>> index 1fee51b72220..3c2948517838 100644
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
>> @@ -11967,12 +11967,27 @@ bpf_sk_base_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>> return func;
>> }
>>
>> +enum skb_dynptr_offset {
>> + SKB_DYNPTR_METADATA = -1,
>
> nit: any reason not do make it 1? The offset is u32, so that -1 reads a bit
> intentional and I don't get the intention :-)
Since we're abusing the "offset" field to serve as an enum tag, I
figured seeing 0xffffffff in a memory dump will be an clear indication
that this is not an offset.
Also, metadata comes before payload, like -1 does before 0...
JK of course. No preference here. Went with my gut.
