From 21ffceda1c8b3807615c40d440d7815e0c85d366 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Tue, 2 Jan 2018 14:01:34 -0500 Subject: alpha: fix crash if pthread_create races with signal delivery On alpha, a process will crash if it attempts to start a thread and a signal is delivered at the same time. The crash can be reproduced with this program: https://cygwin.com/ml/cygwin/2014-11/msg00473.html The reason for the crash is this: * we call the clone syscall * we go to the function copy_process * copy process calls copy_thread_tls, it is a wrapper around copy_thread * copy_thread sets the tls pointer: childti->pcb.unique = regs->r20 * copy_thread sets regs->r20 to zero * we go back to copy_process * copy process checks "if (signal_pending(current))" and returns -ERESTARTNOINTR * the clone syscall is restarted, but this time, regs->r20 is zero, so the new thread is created with zero tls pointer * the new thread crashes in start_thread when attempting to access tls The comment in the code says that setting the register r20 is some compatibility with OSF/1. But OSF/1 doesn't use the CLONE_SETTLS flag, so we don't have to zero r20 if CLONE_SETTLS is set. This patch fixes the bug by zeroing regs->r20 only if CLONE_SETTLS is not set. Signed-off-by: Mikulas Patocka Cc: stable@vger.kernel.org Signed-off-by: Matt Turner --- arch/alpha/kernel/process.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'arch/alpha') diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c index 3af7db4..48b81d0 100644 --- a/arch/alpha/kernel/process.c +++ b/arch/alpha/kernel/process.c @@ -269,12 +269,13 @@ copy_thread(unsigned long clone_flags, unsigned long usp, application calling fork. */ if (clone_flags & CLONE_SETTLS) childti->pcb.unique = regs->r20; + else + regs->r20 = 0; /* OSF/1 has some strange fork() semantics. */ childti->pcb.usp = usp ?: rdusp(); *childregs = *regs; childregs->r0 = 0; childregs->r19 = 0; childregs->r20 = 1; /* OSF/1 has some strange fork() semantics. */ - regs->r20 = 0; stack = ((struct switch_stack *) regs) - 1; *childstack = *stack; childstack->r26 = (unsigned long) ret_from_fork; -- cgit v1.1