From: Jesper Juhl <jj@chaosbits.net>
Date: Mon, 24 Jan 2011 21:41:11 +0000 (+0100)
Subject: x86-64: Don't use pointer to out-of-scope variable in dump_trace()
X-Git-Tag: v2.6.38-rc3~27^2~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2e5aa6824d9e0248d734573dad8858a2cc279cfe;p=pandora-kernel.git

x86-64: Don't use pointer to out-of-scope variable in dump_trace()

In arch/x86/kernel/dumpstack_64.c::dump_trace() we have this code:

...
  		if (!stack) {
  			unsigned long dummy;
  			stack = &dummy;
  			if (task && task != current)
  				stack = (unsigned long *)task->thread.sp;
  		}

  		bp = stack_frame(task, regs);
  		/*
  		 * Print function call entries in all stacks, starting at the
  		 * current stack address. If the stacks consist of nested
  		 * exceptions
  		 */
  		tinfo = task_thread_info(task);

  		for (;;) {
  			char *id;
  			unsigned long *estack_end;
  			estack_end = in_exception_stack(cpu, (unsigned long)stack,
  							&used, &id);
...

You'll notice that we assign to 'stack' the address of the variable
'dummy' which is only in-scope inside the 'if (!stack)'. So when we later
access stack (at the end of the above, and assuming we did not take the
'if (task && task != current)' branch) we'll be using the address of a
variable that is no longer in scope. I believe this patch is the proper
fix, but I freely admit that I'm not 100% certain.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
LKML-Reference: <alpine.LNX.2.00.1101242232590.10252@swampdragon.chaosbits.net>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
---

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