[ 31/54] sparc64: not any error from do_sigaltstack() should fail rt_sigreturn()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

3.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Al Viro <viro@zeniv.linux.org.uk>

commit fae2ae2a900a5c7bb385fe4075f343e7e2d5daa2 upstream.

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.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/sparc/kernel/signal_64.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- 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 *reg
 		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);