Edgar Toernig <froese@xxxxxx> wrote:
> Matthias Lederhofer wrote:
> >
> > +/* if any standard file descriptor is missing open it to /dev/null */
> > +static void sanitize_stdfds(void)
> > +{
> > + int devnull = -1, i;
> > + struct stat buf;
> > + for (i = 0; i < 3; ++i) {
> > + if (fstat(i, &buf) != -1)
> > + continue;
> > + if (devnull == -1 &&
> > + (devnull = open("/dev/null", O_RDWR, 0)) == -1)
> > + die("open /dev/null failed: %s", strerror(errno));
> > + if (dup2(devnull, i) != i)
> > + die("dup2 failed: %s", strerror(errno));
> > + }
> > + if (devnull != -1)
> > + close(devnull);
> > +}
>
> This looks broken. The open will return i as this is
> the lowest free fd. I don't know what POSIX says
> about dup2(i,i) but anyway, you close it at the end
> which completely defeats the intent of the function.
>
> How's this?
>
> devnull = open("/dev/null", O_RDWR, 0);
> if (devnull == 0)
> devnull = dup(devnull);
> if (devnull == 1)
> devnull = dup(devnull);
> if (devnull == -1)
> die("open/dup /dev/null failed: %s", strerror(errno));
> if (devnull > 2)
> close(devnull);
You're right (also for the daemonize function to use sanitize_stdfds).
The code looks good to me, this could also be done using a while-loop
(making it a little bit shorter, I don't know what is easier to read):
devnull = open("/dev/null", O_RDWR, 0);
while (devnull != -1 && devnull < 2)
dup(devnull);
if (devnull == -1)
die("..");
close(devnull);
(This is similar to what Andre Noll posted.)
I'll correct and resend those patches later.
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