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@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 3 deletions

diff --git a/arch/sparc/kernel/signal_64.c b/arch/sparc/kernel/signal_64.c
index 867de2f8189c..689e1ba62809 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);