On Mon, Oct 28, 2019 at 1:59 PM Wenbo Zhang <ethercflow@xxxxxxxxx> wrote: > > When people want to identify which file system files are being opened, > read, and written to, they can use this helper with file descriptor as > input to achieve this goal. Other pseudo filesystems are also supported. > > This requirement is mainly discussed here: > > https://github.com/iovisor/bcc/issues/237 > > v3->v4: > - fix missing fdput() > - move fd2path from kernel/bpf/trace.c to kernel/trace/bpf_trace.c > - move fd2path's test code to another patch > > v2->v3: > - remove unnecessary LOCKDOWN_BPF_READ > - refactor error handling section for enhanced readability > - provide a test case in tools/testing/selftests/bpf > > v1->v2: > - fix backward compatibility > - add this helper description > - fix signed-off name > > Signed-off-by: Wenbo Zhang <ethercflow@xxxxxxxxx> > --- > include/uapi/linux/bpf.h | 14 +++++++++++- > kernel/trace/bpf_trace.c | 40 ++++++++++++++++++++++++++++++++++ > tools/include/uapi/linux/bpf.h | 14 +++++++++++- > 3 files changed, 66 insertions(+), 2 deletions(-) > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > index 4af8b0819a32..124632b2a697 100644 > --- a/include/uapi/linux/bpf.h > +++ b/include/uapi/linux/bpf.h > @@ -2775,6 +2775,17 @@ union bpf_attr { > * restricted to raw_tracepoint bpf programs. > * Return > * 0 on success, or a negative error in case of failure. > + * > + * int bpf_fd2path(char *path, u32 size, int fd) from what I can see, we don't have any BPF helper with this naming approach(2 -> to, 4 -> for, etc). How about something like bpf_get_file_path? > + * Description > + * Get **file** atrribute from the current task by *fd*, then call > + * **d_path** to get it's absolute path and copy it as string into > + * *path* of *size*. The **path** also support pseudo filesystems > + * (whether or not it can be mounted). The *size* must be strictly > + * positive. On success, the helper makes sure that the *path* is > + * NUL-terminated. On failure, it is filled with zeroes. > + * Return > + * 0 on success, or a negative error in case of failure. Mention that we actually return a positive number on success, which is a size of the string + 1 for NUL byte (the +1 is not true right now, but I think should be). > */ > #define __BPF_FUNC_MAPPER(FN) \ > FN(unspec), \ > @@ -2888,7 +2899,8 @@ union bpf_attr { > FN(sk_storage_delete), \ > FN(send_signal), \ > FN(tcp_gen_syncookie), \ > - FN(skb_output), > + FN(skb_output), \ > + FN(fd2path), > > /* 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 571c25d60710..dd7b070df3d6 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -683,6 +683,44 @@ static const struct bpf_func_proto bpf_send_signal_proto = { > .arg1_type = ARG_ANYTHING, > }; > > +BPF_CALL_3(bpf_fd2path, char *, dst, u32, size, int, fd) > +{ > + struct fd f; > + char *p; > + int ret = -EINVAL; > + > + /* Use fdget_raw instead of fdget to support O_PATH */ > + f = fdget_raw(fd); I haven't followed previous discussions, so sorry if this was asked before. Can either fdget_raw or d_path sleep? Also, d_path seems to be relying on current, which in the interrupt context might not be what you really want. Have you considered these problems? > + if (!f.file) > + goto error; > + > + p = d_path(&f.file->f_path, dst, size); > + if (IS_ERR_OR_NULL(p)) { > + ret = PTR_ERR(p); if p can really be NULL, you'd get ret == 0 here, which is probably not what you want. But reading d_path, it seems like it's either valid pointer or error, so just use IS_ERR above? > + goto error; > + } > + > + ret = strlen(p); > + memmove(dst, p, ret); > + dst[ret] = '\0'; I think returning number of useful bytes (including terminating NUL) is good and follows bpf_probe_read_str() convention. So ret++ here? > + goto end; > + > +error: > + memset(dst, '0', size); > +end: > + fdput(f); > + return ret; > +} > + [...]
