linux-kernel - Re: sigaltstack fun

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Message-ID: <20121119023507.GK16916@ZenIV.linux.org.uk>
Date:	Mon, 19 Nov 2012 02:35:07 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	David Miller <davem@...emloft.net>
Cc:	torvalds@...ux-foundation.org, monstr@...str.eu,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: sigaltstack fun

On Sun, Nov 18, 2012 at 08:30:05PM -0500, David Miller wrote:
> > Er...  So which tree should that go through?  sparc or signal?  There's
> > a similar microblaze patch and a few more of the "do_sigaltstack() takes
> > userland pointer" variety, so I can put together a pile in
> > signal.git#for-linus, but if you prefer that to go through sparc tree,
> > I'm fine with that...
> 
> I'm happy to take it via my sparc tree, and I'll queue it up for
> -stable as well. Can you resend it to me with a proper commit message?

sparc64: not any error from do_sigaltstack() should fail rt_sigreturn()

If a signal handler is executed on altstack and another signal comes,
we will end up with rt_sigreturn() on return from the second handler
getting -EPERM from do_sigaltstack().  It's perfectly OK, since we
are not asking to change the settings; in fact, they couldn't have been
changed during the second handler execution exactly because we'd been
on altstack all along.  64bit sigreturn on sparc treats any error from
do_sigaltstack() as "SIGSEGV now"; we need to switch to the same semantics
we are using on other architectures.

Cc: stable@...r.kernel.org
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
diff --git a/arch/sparc/kernel/signal_64.c b/arch/sparc/kernel/signal_64.c
index 867de2f..689e1ba 100644
--- a/arch/sparc/kernel/signal_64.c
+++ b/arch/sparc/kernel/signal_64.c
@@ -295,9 +295,7 @@ void do_rt_sigreturn(struct pt_regs *regs)
 		err |= restore_fpu_state(regs, fpu_save);
 
 	err |= __copy_from_user(&set, &sf->mask, sizeof(sigset_t));
-	err |= do_sigaltstack(&sf->stack, NULL, (unsigned long)sf);
-
-	if (err)
+	if (err || do_sigaltstack(&sf->stack, NULL, (unsigned long)sf) == -EFAULT)
 		goto segv;
 
 	err |= __get_user(rwin_save, &sf->rwin_save);
--
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