Messages in this thread | | | Date | Mon, 22 Jan 2007 09:52:59 -0500 | From | Neil Horman <> | Subject | Re: [PATCH] select: fix sys_select to not leak ERESTARTNOHAND to userspace |
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On Mon, Jan 22, 2007 at 02:59:56PM +0100, Paolo Ornati wrote: > On Tue, 16 Jan 2007 15:13:32 -0500 > Neil Horman <nhorman@tuxdriver.com> 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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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