On Fri, Dec 23, 2022 at 5:36 AM Xin Liu <liuxin350@xxxxxxxxxx> wrote:
>
> In the ensure_good_fd function, if the fcntl function succeeds but
> the close function fails, ensure_good_fd returns a normal fd and
> sets errno, which may cause users to misunderstand. The close
> failure is not a serious problem, and the correct FD has been
> handed over to the upper-layer application. Let's restore errno here.
>
> Signed-off-by: Xin Liu <liuxin350@xxxxxxxxxx>
> ---
> tools/lib/bpf/libbpf_internal.h | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> index 377642ff51fc..98333a6c38e9 100644
> --- a/tools/lib/bpf/libbpf_internal.h
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -543,10 +543,9 @@ static inline int ensure_good_fd(int fd)
> fd = fcntl(fd, F_DUPFD_CLOEXEC, 3);
> saved_errno = errno;
> close(old_fd);
> - if (fd < 0) {
> + errno = saved_errno;
> + if (fd < 0)
> pr_warn("failed to dup FD %d to FD > 2: %d\n", old_fd, -saved_errno);
> - errno = saved_errno;
pr_warn calls into user-provided callback, which can clobber errno, so
`errno = saved_errno` should happen after pr_warn. With your change
there is even higher chance of errno clobbering.
Please send a follow up fix to unconditionally restore errno *after*
pr_warn, thanks.
> - }
> }
> return fd;
> }
> --
> 2.33.0
>
