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| author | Mikulas Patocka <mpatocka@redhat.com> | 2018-01-02 20:01:34 +0100 |
|---|---|---|
| committer | Matt Turner <mattst88@gmail.com> | 2018-01-21 02:01:16 +0100 |
| commit | 21ffceda1c8b3807615c40d440d7815e0c85d366 (patch) | |
| tree | 6c8285ff86912843ce4b1f4335ad5bbdeb50b4f7 /arch/alpha | |
| parent | alpha: fix formating of stack content (diff) | |
| download | linux-21ffceda1c8b3807615c40d440d7815e0c85d366.tar.xz linux-21ffceda1c8b3807615c40d440d7815e0c85d366.zip | |
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 <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Matt Turner <mattst88@gmail.com>
Diffstat (limited to 'arch/alpha')
| -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 3af7db471029..48b81d015d8a 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; |