On Mon, Feb 1, 2021 at 11:37 PM Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > On Mon, Feb 1, 2021 at 2:32 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: > > > > On 1/30/21 12:45 PM, Florent Revest wrote: > > > On Fri, Jan 29, 2021 at 1:49 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: > > >> On 1/29/21 11:57 AM, Daniel Borkmann wrote: > > >>> On 1/27/21 10:01 PM, Andrii Nakryiko wrote: > > >>>> On Tue, Jan 26, 2021 at 10:36 AM Florent Revest <revest@xxxxxxxxxxxx> wrote: > > >>>>> > > >>>>> This needs a new helper that: > > >>>>> - can work in a sleepable context (using sock_gen_cookie) > > >>>>> - takes a struct sock pointer and checks that it's not NULL > > >>>>> > > >>>>> Signed-off-by: Florent Revest <revest@xxxxxxxxxxxx> > > >>>>> Acked-by: KP Singh <kpsingh@xxxxxxxxxx> > > >>>>> --- > > >>>>> include/linux/bpf.h | 1 + > > >>>>> include/uapi/linux/bpf.h | 8 ++++++++ > > >>>>> kernel/trace/bpf_trace.c | 2 ++ > > >>>>> net/core/filter.c | 12 ++++++++++++ > > >>>>> tools/include/uapi/linux/bpf.h | 8 ++++++++ > > >>>>> 5 files changed, 31 insertions(+) > > >>>>> > > >>>>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h > > >>>>> index 1aac2af12fed..26219465e1f7 100644 > > >>>>> --- a/include/linux/bpf.h > > >>>>> +++ b/include/linux/bpf.h > > >>>>> @@ -1874,6 +1874,7 @@ extern const struct bpf_func_proto bpf_per_cpu_ptr_proto; > > >>>>> extern const struct bpf_func_proto bpf_this_cpu_ptr_proto; > > >>>>> extern const struct bpf_func_proto bpf_ktime_get_coarse_ns_proto; > > >>>>> extern const struct bpf_func_proto bpf_sock_from_file_proto; > > >>>>> +extern const struct bpf_func_proto bpf_get_socket_ptr_cookie_proto; > > >>>>> > > >>>>> const struct bpf_func_proto *bpf_tracing_func_proto( > > >>>>> enum bpf_func_id func_id, const struct bpf_prog *prog); > > >>>>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > > >>>>> index 0b735c2729b2..5855c398d685 100644 > > >>>>> --- a/include/uapi/linux/bpf.h > > >>>>> +++ b/include/uapi/linux/bpf.h > > >>>>> @@ -1673,6 +1673,14 @@ union bpf_attr { > > >>>>> * Return > > >>>>> * A 8-byte long unique number. > > >>>>> * > > >>>>> + * u64 bpf_get_socket_cookie(void *sk) > > >>>> > > >>>> should the type be `struct sock *` then? > > >>> > > >>> Checking libbpf's generated bpf_helper_defs.h it generates: > > >>> > > >>> /* > > >>> * bpf_get_socket_cookie > > >>> * > > >>> * If the **struct sk_buff** pointed by *skb* has a known socket, > > >>> * retrieve the cookie (generated by the kernel) of this socket. > > >>> * If no cookie has been set yet, generate a new cookie. Once > > >>> * generated, the socket cookie remains stable for the life of the > > >>> * socket. This helper can be useful for monitoring per socket > > >>> * networking traffic statistics as it provides a global socket > > >>> * identifier that can be assumed unique. > > >>> * > > >>> * Returns > > >>> * A 8-byte long non-decreasing number on success, or 0 if the > > >>> * socket field is missing inside *skb*. > > >>> */ > > >>> static __u64 (*bpf_get_socket_cookie)(void *ctx) = (void *) 46; > > >>> > > >>> So in terms of helper comment it's picking up the description from the > > >>> `u64 bpf_get_socket_cookie(struct sk_buff *skb)` signature. With that > > >>> in mind it would likely make sense to add the actual `struct sock *` type > > >>> to the comment to make it more clear in here. > > >> > > >> One thought that still came to mind when looking over the series again, do > > >> we need to blacklist certain functions from bpf_get_socket_cookie() under > > >> tracing e.g. when attaching to, say fexit? For example, if sk_prot_free() > > >> would be temporary uninlined/exported for testing and bpf_get_socket_cookie() > > >> was invoked from a prog upon fexit where sock was already passed back to > > >> allocator, I presume there's risk of mem corruption, no? > > > > > > Mh, this is interesting. I can try to add a deny list in v7 but I'm > > > not sure whether I'll be able to catch them all. I'm assuming that > > > __sk_destruct, sk_destruct, __sk_free, sk_free would be other > > > problematic functions but potentially there would be more. > > > > I was just looking at bpf_skb_output() from a7658e1a4164 ("bpf: Check types of > > arguments passed into helpers") which afaiu has similar issue, back at the time > > this was introduced there was no fentry/fexit but rather raw tp progs, so you > > could still safely dump skb this way including for kfree_skb() tp. Presumably if > > you bpf_skb_output() at 'fexit/kfree_skb' you might be able to similarly crash > > the verifier cannot check absolutely everything. > Whitelisting and blacklisting all combinations is not practical. Ok, I'm sending a v7 that only changes the signature to take a struct sock * argument then and I won't be adding an allow or deny list in this series. :) > > your kernel which I don't think is intentional (also given we go above and beyond > > in other areas to avoid crashing or destabilizing e.g. [0] to mention one). Maybe > > these should really only be for BPF_TRACE_RAW_TP (or BPF_PROG_TYPE_LSM) where it > > can be audited that it's safe to use like a7658e1a4164's original intention ... > > or have some sort of function annotation like __acquires/__releases but for tracing > > e.g. __frees(skb) where use would then be blocked (not sure iff feasible). > > I think this set is useful and corner cases like fexit in sk_free are > not worth the hassle. > One can install xdp prog that drops all packets. The server is dead at > this point.