lkml.org 
[lkml]   [2022]   [Dec]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH bpf-next] libbpf: fix errno is overwritten after being closed.
On Fri, Dec 23, 2022 at 5:36 AM Xin Liu <liuxin350@huawei.com> 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@huawei.com>
> ---
> 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
>

\
 
 \ /
  Last update: 2023-03-26 23:23    [W:0.098 / U:0.824 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site