On Fri, Jun 26, 2020 at 01:38:27PM -0700, Andrii Nakryiko wrote:
> On Thu, Jun 25, 2020 at 4:49 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > Adding d_path helper function that returns full path
> > for give 'struct path' object, which needs to be the
> > kernel BTF 'path' object.
> >
> > The helper calls directly d_path function.
> >
> > Updating also bpf.h tools uapi header and adding
> > 'path' to bpf_helpers_doc.py script.
> >
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> > include/uapi/linux/bpf.h | 14 +++++++++-
> > kernel/trace/bpf_trace.c | 47 ++++++++++++++++++++++++++++++++++
> > scripts/bpf_helpers_doc.py | 2 ++
> > tools/include/uapi/linux/bpf.h | 14 +++++++++-
> > 4 files changed, 75 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 0cb8ec948816..23274c81f244 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -3285,6 +3285,17 @@ union bpf_attr {
> > * Dynamically cast a *sk* pointer to a *udp6_sock* pointer.
> > * Return
> > * *sk* if casting is valid, or NULL otherwise.
> > + *
> > + * int bpf_d_path(struct path *path, char *buf, u32 sz)
> > + * Description
> > + * Return full path for given 'struct path' object, which
> > + * needs to be the kernel BTF 'path' object. The path is
> > + * returned in buffer provided 'buf' of size 'sz'.
> > + *
> > + * Return
> > + * length of returned string on success, or a negative
> > + * error in case of failure
>
> It's important to note whether string is always zero-terminated (I'm
> guessing it is, right?).
right, will add
>
> > + *
> > */
> > #define __BPF_FUNC_MAPPER(FN) \
> > FN(unspec), \
> > @@ -3427,7 +3438,8 @@ union bpf_attr {
> > FN(skc_to_tcp_sock), \
> > FN(skc_to_tcp_timewait_sock), \
> > FN(skc_to_tcp_request_sock), \
> > - FN(skc_to_udp6_sock),
> > + FN(skc_to_udp6_sock), \
> > + FN(d_path),
> >
> > /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> > * function eBPF program intends to call
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index b124d468688c..6f31e21565b6 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -1060,6 +1060,51 @@ static const struct bpf_func_proto bpf_send_signal_thread_proto = {
> > .arg1_type = ARG_ANYTHING,
> > };
> >
> > +BPF_CALL_3(bpf_d_path, struct path *, path, char *, buf, u32, sz)
> > +{
> > + char *p = d_path(path, buf, sz - 1);
> > + int len;
> > +
> > + if (IS_ERR(p)) {
> > + len = PTR_ERR(p);
> > + } else {
> > + len = strlen(p);
> > + if (len && p != buf) {
> > + memmove(buf, p, len);
> > + buf[len] = 0;
>
> if len above is zero, you won't zero-terminate it, so probably better
> to move buf[len] = 0 out of if to do unconditionally
good catch, will change
>
> > + }
> > + }
> > +
> > + return len;
> > +}
> > +
> > +BTF_SET_START(btf_whitelist_d_path)
> > +BTF_ID(func, vfs_truncate)
> > +BTF_ID(func, vfs_fallocate)
> > +BTF_ID(func, dentry_open)
> > +BTF_ID(func, vfs_getattr)
> > +BTF_ID(func, filp_close)
> > +BTF_SET_END(btf_whitelist_d_path)
> > +
> > +static bool bpf_d_path_allowed(const struct bpf_prog *prog)
> > +{
> > + return btf_id_set_contains(&btf_whitelist_d_path, prog->aux->attach_btf_id);
> > +}
> > +
>
> This looks pretty great and clean, considering what's happening under
> the covers. Nice work, thanks a lot!
>
> > +BTF_ID_LIST(bpf_d_path_btf_ids)
> > +BTF_ID(struct, path)
>
> this is a bit more confusing to read and error-prone, but I couldn't
> come up with any better way to do this... Still better than
> alternatives.
>
> > +
> > +static const struct bpf_func_proto bpf_d_path_proto = {
> > + .func = bpf_d_path,
> > + .gpl_only = true,
>
> Does it have to be GPL-only? What's the criteria? Sorry if this was
> brought up previously.
I don't think it's needed to be gpl_only, I'll set it to false
thanks,
jirka
