diff options
| author | Mikulas Patocka <mpatocka@redhat.com> | 2018-01-02 14:01:34 -0500 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-02-17 13:21:19 +0100 |
| commit | 68d18e90eeec864b38e1313e0d6d10b4e1e5a1fc (patch) | |
| tree | 08b68feb33d7c95f690838bd9d2d40c8565e5f83 | |
| parent | 21f94109d0f17d2fb775ae0e51ef98feda2b9a47 (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>
| -rw-r--r-- | arch/alpha/kernel/process.c | 3 |
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; |