Re: [PATCH] PPC32: cancel syscall restart on signal delivery

[Paul Mackerras <paulus@samba.org>]

Linus Torvalds writes:

> Excellent point. We're actually much better off resetting it at signal
> return.
> 
> Which should make all other resets unnecessary.

Yes.

> Yes, you can get out of a signal by using longjmp, but that doesn't
> matter: you can't longjump to a restart call (well, you can, but only if
> the user literally tries to do the restart by hand, ie he _intended_ to do
> it).
> 
> So the _proper_ fix (for x86) should be as appended. Agreed?

Agreed.  Here is the patch for PPC.

Thanks,
Paul.

diff -urN linux-2.5/arch/ppc/kernel/signal.c pmac-2.5/arch/ppc/kernel/signal.c
--- linux-2.5/arch/ppc/kernel/signal.c	2003-11-15 16:55:18.618797320 +1100
+++ pmac-2.5/arch/ppc/kernel/signal.c	2003-11-15 17:09:53.145849000 +1100
@@ -418,6 +418,9 @@
 {
 	struct rt_sigframe __user *rt_sf;
 
+	/* Always make any pending restarted system calls return -EINTR */
+	current_thread_info()->restart_block.fn = do_no_restart_syscall;
+
 	rt_sf = (struct rt_sigframe __user *)
 		(regs->gpr[1] + __SIGNAL_FRAMESIZE + 16);
 	if (verify_area(VERIFY_READ, rt_sf, sizeof(struct rt_sigframe)))
@@ -513,6 +516,9 @@
 	struct mcontext __user *sr;
 	sigset_t set;
 
+	/* Always make any pending restarted system calls return -EINTR */
+	current_thread_info()->restart_block.fn = do_no_restart_syscall;
+
 	sc = (struct sigcontext __user *)(regs->gpr[1] + __SIGNAL_FRAMESIZE);
 	if (copy_from_user(&sigctx, sc, sizeof(sigctx)))
 		goto badframe;
@@ -583,9 +589,6 @@
 	if (signr == 0)
 		return 0;		/* no signals delivered */
 
-	/* Always make any pending restarted system calls return -EINTR */
-	current_thread_info()->restart_block.fn = do_no_restart_syscall;
-
 	if ((ka->sa.sa_flags & SA_ONSTACK) && current->sas_ss_size
 	    && !on_sig_stack(regs->gpr[1]))
 		newsp = current->sas_ss_sp + current->sas_ss_size;