[PATCH] posix: Handle negative fds in spawn's addfchdir

[Collin Funk]

Lucas Chollet <lucas.chollet@free.fr> writes:

> Hello all,
> This is my first contribution here, so I hope I got everything right.
> I tested this patch on my Linux x86_64 machine with `make check` and
> got no regressions compared to master.
>
> 8<
>
> This patch makes `posix_spawn_file_actions_addfchdir` return EBADF on
> negative file descriptors. This is mandated by POSIX and similar to what
> is already done in addopen/addclose.
>
> Signed-off-by: Lucas Chollet <lucas.chollet@free.fr>
> ---
>  posix/spawn_faction_addfchdir.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/posix/spawn_faction_addfchdir.c b/posix/spawn_faction_addfchdir.c
> index a3df6df489..b51139a61f 100644
> --- a/posix/spawn_faction_addfchdir.c
> +++ b/posix/spawn_faction_addfchdir.c
> @@ -28,6 +28,9 @@ posix_spawn_file_actions_addfchdir_np (posix_spawn_file_actions_t *actions,
>  {
>    struct __spawn_action *rec;
>  
> +  if (!__spawn_valid_fd (fd))
> +    return EBADF;
> +
>    /* Allocate more memory if needed.  */
>    if (actions->__used == actions->__allocated
>        && __posix_spawn_file_actions_realloc (actions) != 0)

Thank you for the patch!

However, I want to note here that __spawn_valid_fd() checks if the file
descriptor is greater than getdtablesize(). Using it here, along with
some (all?) other places it is used, is incorrect. POSIX states [1]:

    [EBADF]
        The value specified by fildes is negative.

    It shall not be considered an error for the path or fildes argument
    passed to these functions to specify a pathname or file descriptor
    for which the specified operation could not be performed at the time
    of the call. Any such error shall be detected when the associated
    file actions object is later used during a posix_spawn() or
    posix_spawnp() operation.

I noticed glibc's misbehavior when working on Gnulib last year, but
evidently forgot to fix it...

Collin

[1] https://pubs.opengroup.org/onlinepubs/9799919799/functions/posix_spawn_file_actions_addchdir.html
[2] https://lists.gnu.org/archive/html/bug-gnulib/2025-10/msg00118.html