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authorMikulas Patocka <mpatocka@redhat.com>2018-01-02 14:01:34 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-02-17 13:21:19 +0100
commit68d18e90eeec864b38e1313e0d6d10b4e1e5a1fc (patch)
tree08b68feb33d7c95f690838bd9d2d40c8565e5f83 /arch/alpha
parent21f94109d0f17d2fb775ae0e51ef98feda2b9a47 (diff)
alpha: fix crash if pthread_create races with signal delivery
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>
Diffstat (limited to 'arch/alpha')
-rw-r--r--arch/alpha/kernel/process.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
index b483156698d5..60c17b9bf04d 100644
--- a/arch/alpha/kernel/process.c
+++ b/arch/alpha/kernel/process.c
@@ -265,12 +265,13 @@ 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;