diff options
| author | Mikulas Patocka <mpatocka@redhat.com> | 2018-01-02 14:01:34 -0500 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2018-06-01 00:30:09 +0100 |
| commit | 629bfb9f6b0d47c4ec805ec587acca059b68e924 (patch) | |
| tree | 35da2984442064d3f905eaf2001dc2a107ae5f00 | |
| parent | 33d0141f9db7664a04bfb17a576867c0122f226a (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>
[bwh: Backported to 3.2:
- Remove the settls variable, which was done upstream in commit 25906730ec01
"alpha: reorganize copy_process(), prepare to saner fork_idle()"]
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
| -rw-r--r-- | arch/alpha/kernel/process.c | 12 |
1 files changed, 5 insertions, 7 deletions
diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c index 89bbe5b41145..42c2481535dc 100644 --- a/arch/alpha/kernel/process.c +++ b/arch/alpha/kernel/process.c @@ -279,7 +279,7 @@ copy_thread(unsigned long clone_flags, unsigned long usp, struct thread_info *childti = task_thread_info(p); struct pt_regs * childregs; struct switch_stack * childstack, *stack; - unsigned long stack_offset, settls; + unsigned long stack_offset; stack_offset = PAGE_SIZE - sizeof(struct pt_regs); if (!(regs->ps & 8)) @@ -288,11 +288,9 @@ copy_thread(unsigned long clone_flags, unsigned long usp, (stack_offset + PAGE_SIZE + task_stack_page(p)); *childregs = *regs; - settls = regs->r20; 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 = ((struct switch_stack *) childregs) - 1; *childstack = *stack; @@ -302,16 +300,16 @@ copy_thread(unsigned long clone_flags, unsigned long usp, childti->pcb.flags = 1; /* set FEN, clear everything else */ /* Set a new TLS for the child thread? Peek back into the - syscall arguments that we saved on syscall entry. Oops, - except we'd have clobbered it with the parent/child set - of r20. Read the saved copy. */ + syscall arguments that we saved on syscall entry. */ /* Note: if CLONE_SETTLS is not set, then we must inherit the value from the parent, which will have been set by the block copy in dup_task_struct. This is non-intuitive, but is required for proper operation in the case of a threaded application calling fork. */ if (clone_flags & CLONE_SETTLS) - childti->pcb.unique = settls; + childti->pcb.unique = regs->r20; + else + regs->r20 = 0; /* OSF/1 has some strange fork() semantics. */ return 0; } |