On 9/7/22 11:31 AM, Joanne Koong wrote:
For bpf prog types that don't support writes on skb data, the dynptr is
read-only (bpf_dynptr_write() will return an error and bpf_dynptr_data()
will return NULL; for a read-only data slice, there will be a separate
API bpf_dynptr_data_rdonly(), which will be added in the near future).
I just caught up on the v4 discussion about loadtime-vs-runtime error on
write. From a user perspective, I am not concerned on which error.
Either way, I will quickly find out the packet header is not changed.
For the dynptr init helper bpf_dynptr_from_skb(), the user does not need
to know its skb is read-only or not and uses the same helper. The
verifier in this case uses its knowledge on the skb context and uses
bpf_dynptr_from_skb_rdonly_proto or bpf_dynptr_from_skb_rdwr_proto
accordingly.
Now for the slice helper, the user needs to remember its skb is read
only (or not) and uses bpf_dynptr_data() vs bpf_dynptr_data_rdonly()
accordingly. Yes, if it only needs to read, the user can always stay
with bpf_dynptr_data_rdonly (which is not the initially supported one
though). However, it is still unnecessary burden and surprise to user.
It is likely it will silently turn everything into bpf_dynptr_read()
against the user intention. eg:
if (bpf_dynptr_from_skb(skb, 0, &dynptr))
return 0;
ip6h = bpf_dynptr_data(&dynptr, 0, sizeof(*ip6h));
if (!ip6h) {
/* Unlikely case, in non-linear section, just bpf_dynptr_read()
* Oops...actually bpf_dynptr_data_rdonly() should be used.
*/
bpf_dynptr_read(buf, sizeof(*ip6h), &dynptr, 0, 0);
ip6h = buf;
}
+ case BPF_DYNPTR_TYPE_SKB:
+ {
+ struct sk_buff *skb = ptr->data;
+
+ /* if the data is paged, the caller needs to pull it first */
+ if (ptr->offset + offset + len > skb->len - skb->data_len)
nit. skb_headlen(skb)
The patches can't be applied cleanly also. Please remember to rebase.
eg. commit afef88e65554 ("selftests/bpf: Store BPF object files with
.bpf.o extension") has landed on Sep 2.
