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ARM: fix /proc/$PID/stack on SMP

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Rabin Vincent reports:
| On SMP, this BUG() in save_stack_trace_tsk() can be easily triggered
| from user space by reading /proc/$PID/stack, where $PID is any pid but
| the current process:
|
|	if (tsk != current) {
| #ifdef CONFIG_SMP
|		/*
|		 * What guarantees do we have here that 'tsk'
|		 * is not running on another CPU?
|		 */
|		BUG();
| #else

Fix this by replacing the BUG() with an entry to terminate the stack
trace, returning an empty trace - I'd rather not expose the dwarf
unwinder to a volatile stack of a running thread.

Reported-by: Rabin Vincent <rabin@rab.in>
Tested-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Russell King 2011-01-15 09:27:04 +00:00
parent 671289c287
commit d5996b2ff0
1 changed files with 6 additions and 3 deletions
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9
arch/arm/kernel/stacktrace.c
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@ -94,10 +94,13 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
if (tsk != current) {
#ifdef CONFIG_SMP
/*
* What guarantees do we have here that 'tsk'
* is not running on another CPU?
* What guarantees do we have here that 'tsk' is not
* running on another CPU? For now, ignore it as we
* can't guarantee we won't explode.
*/
BUG();
if (trace->nr_entries < trace->max_entries)
trace->entries[trace->nr_entries++] = ULONG_MAX;
return;
#else
data.no_sched_functions = 1;
frame.fp = thread_saved_fp(tsk);