> [...]
>>> + * On failure, it is filled with zeroes.
> [...]
> You fill it with 0x30's ...
So sorry about this, I'll submit another revision to fix this. Thanks
again for your
preciseness and patience.
Daniel Borkmann <daniel@xxxxxxxxxxxxx> 于2019年12月18日周三 上午3:39写道：
>
> On 12/17/19 5:29 PM, Yonghong Song wrote:
> > On 12/17/19 1:47 AM, Wenbo Zhang wrote:
> [...]
> >> + * On failure, it is filled with zeroes.
> [...]
> >> */
> >> #define __BPF_FUNC_MAPPER(FN) \
> >> FN(unspec), \
> >> @@ -2938,7 +2964,8 @@ union bpf_attr {
> >> FN(probe_read_user), \
> >> FN(probe_read_kernel), \
> >> FN(probe_read_user_str), \
> >> - FN(probe_read_kernel_str),
> >> + FN(probe_read_kernel_str), \
> >> + FN(get_fd_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 e5ef4ae9edb5..43a6aa6ad967 100644
> >> --- a/kernel/trace/bpf_trace.c
> >> +++ b/kernel/trace/bpf_trace.c
> >> @@ -762,6 +762,71 @@ static const struct bpf_func_proto bpf_send_signal_proto = {
> >> .arg1_type = ARG_ANYTHING,
> >> };
> >>
> >> +BPF_CALL_3(bpf_get_fd_path, char *, dst, u32, size, int, fd)
> >> +{
> >> + int ret = -EBADF;
> >> + struct file *f;
> >> + char *p;
> >> +
> >> + /* Ensure we're in user context which is safe for the helper to
> >> + * run. This helper has no business in a kthread.
> >> + */
> >> + if (unlikely(in_interrupt() ||
> >> + current->flags & (PF_KTHREAD | PF_EXITING))) {
> >> + ret = -EPERM;
> >> + goto error;
> >> + }
> >> +
> >> + /* Use fget_raw instead of fget to support O_PATH, and it doesn't
> >> + * have any sleepable code, so it's ok to be here.
> >> + */
> >> + f = fget_raw(fd);
> >> + if (!f)
> >> + goto error;
> >> +
> >> + /* For unmountable pseudo filesystem, it seems to have no meaning
> >> + * to get their fake paths as they don't have path, and to be no
> >> + * way to validate this function pointer can be always safe to call
> >> + * in the current context.
> >> + */
> >> + if (f->f_path.dentry->d_op && f->f_path.dentry->d_op->d_dname) {
> >> + ret = -EINVAL;
> >> + fput(f);
> >> + goto error;
> >> + }
> >> +
> >> + /* After filter unmountable pseudo filesytem, d_path won't call
> >> + * dentry->d_op->d_name(), the normally path doesn't have any
> >> + * sleepable code, and despite it uses the current macro to get
> >> + * fs_struct (current->fs), we've already ensured we're in user
> >> + * context, so it's ok to be here.
> >> + */
> >> + p = d_path(&f->f_path, dst, size);
> >> + if (IS_ERR(p)) {
> >> + ret = PTR_ERR(p);
> >> + fput(f);
> >> + goto error;
> >> + }
> >> +
> >> + ret = strlen(p) + 1;
> >> + memmove(dst, p, ret);
> >> + fput(f);
> >> + return ret;
> >> +
> >> +error:
> >> + memset(dst, '0', size);
>
> You fill it with 0x30's ...
>
> >> + return ret;
> >> +}
