When entering the scheduler from the signal handler, tell

the kernel to (re)use the alternate signal stack.  In this
case, we don't return normally from the signal handler,
so the kernel still thinks we are using the signal stack.
The fixes a nasty bug where the signal handler can start
fiddling with the stack of a thread while the handler is
actually running on the same stack.

MFC candidate

1 files changed, 9 insertions, 6 deletions

diff --git a/lib/libc_r/uthread/uthread_init.c b/lib/libc_r/uthread/uthread_init.c
index 35731c4..be671a1 100644
--- a/lib/libc_r/uthread/uthread_init.c
+++ b/lib/libc_r/uthread/uthread_init.c
@@ -92,7 +92,6 @@ _thread_init(void)
 	int		mib[2];
 	struct clockinfo clockinfo;
 	struct sigaction act;
-	struct sigaltstack alt;
 
 	/* Check if this function has already been called: */
 	if (_thread_initial)
@@ -281,11 +280,15 @@ _thread_init(void)
 		/* Clear the signal queue: */
 		memset(_thread_sigq, 0, sizeof(_thread_sigq));
 
-		/* Create and install an alternate signal stack: */
-		alt.ss_sp = malloc(SIGSTKSZ);	/* recommended stack size */
-		alt.ss_size = SIGSTKSZ;
-		alt.ss_flags = 0;
-		if (_thread_sys_sigaltstack(&alt, NULL) != 0)
+		/*
+		 * Create and install an alternate signal stack of
+		 * the recommended size:
+		 */
+		_thread_sigstack.ss_sp = malloc(SIGSTKSZ);
+		_thread_sigstack.ss_size = SIGSTKSZ;
+		_thread_sigstack.ss_flags = 0;
+		if ((_thread_sigstack.ss_sp == NULL) ||
+		    (_thread_sys_sigaltstack(&_thread_sigstack, NULL) != 0))
 			PANIC("Unable to install alternate signal stack");
 
 		/* Enter a loop to get the existing signal status: */