This is a note to let you know that I've just added the patch titled
alpha: fix crash if pthread_create races with signal delivery
to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: alpha-fix-crash-if-pthread_create-races-with-signal-delivery.patch and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From 21ffceda1c8b3807615c40d440d7815e0c85d366 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka mpatocka@redhat.com Date: Tue, 2 Jan 2018 14:01:34 -0500 Subject: alpha: fix crash if pthread_create races with signal delivery
From: Mikulas Patocka mpatocka@redhat.com
commit 21ffceda1c8b3807615c40d440d7815e0c85d366 upstream.
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 mpatocka@redhat.com Signed-off-by: Matt Turner mattst88@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/alpha/kernel/process.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/arch/alpha/kernel/process.c +++ b/arch/alpha/kernel/process.c @@ -273,12 +273,13 @@ copy_thread(unsigned long clone_flags, u 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;
Patches currently in stable-queue which might be from mpatocka@redhat.com are
queue-4.4/alpha-fix-crash-if-pthread_create-races-with-signal-delivery.patch queue-4.4/alpha-fix-reboot-on-avanti-platform.patch