On Mon, Jan 22, 2007 at 02:59:56PM +0100, Paolo Ornati wrote:
> On Tue, 16 Jan 2007 15:13:32 -0500
> Neil Horman <[email protected]> wrote:
>
> > As it is currently written, sys_select checks its return code to convert
> > ERESTARTNOHAND to EINTR. However, the check is within an if (tvp) clause, and
> > so if select is called from userspace with a NULL timeval, then it is possible
> > for the ERESTARTNOHAND errno to leak into userspace, which is incorrect. This
> > patch moves that check outside of the conditional, and prevents the errno leak.
>
> the ERESTARTNOHAND thing is handled in arch specific signal code,
In the signal handling path yes.
Not always in the case of select, though. Check core_sys_select:
if (!ret) {
ret = -ERESTARTNOHAND;
if (signal_pending(current))
goto out;
ret = 0;
}
...
out:
if (bits != stack_fds)
kfree(bits);
out_nofds:
return ret;
Its possible for core_sys_select to return ERESTARTNOHAND to sys_select, which
will in turn (as its currently written), return that value back to user space.
> syscalls can return -ERESTARTNOHAND as much as they want (and your
> change breaks the current behaviour of select()).
>
It doesn't break it, it fixes it. select isn't meant to ever return
ERESTARTNOHAND to user space:
http://www.opengroup.org/onlinepubs/009695399/functions/select.html
And ENORESTARTHAND isn't defined in the userspace errno.h, so this causes all
sorts of confusion for apps that don't expect it.
Neil
> For example:
>
> arch/x86_64/kernel/signal.c
>
> /* Are we from a system call? */
> if ((long)regs->orig_rax >= 0) {
> /* If so, check system call restarting.. */
> switch (regs->rax) {
> case -ERESTART_RESTARTBLOCK:
> case -ERESTARTNOHAND:
> regs->rax = -EINTR;
> break;
>
> --
> Paolo Ornati
> Linux 2.6.20-rc5 on x86_64
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