> Also I'd prefer fdget_*()'s error path not calling fdput(f). Thank you, I've committed a new patch to fix this. Daniel Borkmann <daniel@xxxxxxxxxxxxx> 于2019年10月30日周三 下午11:32写道： > > On Tue, Oct 29, 2019 at 11:48:44AM -0700, Andrii Nakryiko wrote: > > 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); > > Also I'd prefer fdget_*()'s error path not calling fdput(f). > > > > + return ret; > > > +} > > > + > > > > [...]
