Re: [PATCH bpf-next] libbpf: keep FD_CLOEXEC flag when dup()'ing FD

[Lennart Poettering <lennart@poettering.net>]

On Mi, 29.05.24 15:32, Andrii Nakryiko (andrii@kernel.org) wrote:

> Make sure to preserve and/or enforce FD_CLOEXEC flag on duped FDs.
> Use dup3() with O_CLOEXEC flag for that.
>
> Without this fix libbpf effectively clears FD_CLOEXEC flag on each of BPF
> map/prog FD, which is definitely not the right or expected behavior.

Thanks!

lgtm, superficially.

> Reported-by: Lennart Poettering <lennart@poettering.net>
> Fixes: bc308d011ab8 ("libbpf: call dup2() syscall directly")
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
>  tools/lib/bpf/libbpf_internal.h | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> index a0dcfb82e455..7e7e686008c6 100644
> --- a/tools/lib/bpf/libbpf_internal.h
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -597,13 +597,9 @@ static inline int ensure_good_fd(int fd)
>  	return fd;
>  }
>
> -static inline int sys_dup2(int oldfd, int newfd)
> +static inline int sys_dup3(int oldfd, int newfd, int flags)
>  {
> -#ifdef __NR_dup2
> -	return syscall(__NR_dup2, oldfd, newfd);
> -#else
> -	return syscall(__NR_dup3, oldfd, newfd, 0);
> -#endif
> +	return syscall(__NR_dup3, oldfd, newfd, flags);
>  }
>
>  /* Point *fixed_fd* to the same file that *tmp_fd* points to.
> @@ -614,7 +610,7 @@ static inline int reuse_fd(int fixed_fd, int tmp_fd)
>  {
>  	int err;
>
> -	err = sys_dup2(tmp_fd, fixed_fd);
> +	err = sys_dup3(tmp_fd, fixed_fd, O_CLOEXEC);
>  	err = err < 0 ? -errno : 0;
>  	close(tmp_fd); /* clean up temporary FD */
>  	return err;
> --
> 2.43.0
>
>

Lennart

--
Lennart Poettering, Berlin