Re: [PATCH v2 12/26] qga: replace pipe() with g_unix_open_pipe(CLOEXEC)

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Apr 27, 2022 at 12:24:44PM +0400, Marc-André Lureau wrote:
> Hi
> 
> On Wed, Apr 27, 2022 at 5:08 AM Richard Henderson <
> richard.henderson@linaro.org> wrote:
> 
> > On 4/26/22 02:27, marcandre.lureau@redhat.com wrote:
> > > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > >
> > > Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
> > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > ---
> > >   qga/commands-posix.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> > > index 77f4672ca2c9..094487c2c395 100644
> > > --- a/qga/commands-posix.c
> > > +++ b/qga/commands-posix.c
> > > @@ -2529,7 +2529,7 @@ void qmp_guest_set_user_password(const char
> > *username,
> > >           goto out;
> > >       }
> > >
> > > -    if (pipe(datafd) < 0) {
> > > +    if (!g_unix_open_pipe(datafd, FD_CLOEXEC, NULL)) {
> > >           error_setg(errp, "cannot create pipe FDs");
> > >           goto out;
> > >       }
> >
> > This looks wrong, since the next thing that happens is fork+execl.
> >
> >
> Before exec(), it does
>         close(datafd[1]);
>         dup2(datafd[0], 0);
> 
> 0, the newfd, does not share file descriptor flags (the close-on-exec flag).
> 
> I did a quick test, and it seems to be fine.

The 'dup' man page says

       The  two  file  descriptors do not share file descriptor flags
       (the close-on-exec flag).  The close-on-exec flag (FD_CLOEXEC;
       see fcntl(2)) for the duplicate descriptor is off.

so we're fine in this respect. You could need to use dup3 to explicitly
turn on FD_CLOEXEC on the duplicate, so

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


With regards,
Daniel
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