[patch] x86: avoid dereferencing beyond stack + THREAD_SIZE

[David Rientjes]

It's possible for get_wchan() to dereference past task->stack + THREAD_SIZE 
while iterating through instruction pointers if fp equals the upper boundary, 
causing a kernel panic.

Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
 arch/x86/kernel/process_64.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -729,12 +729,12 @@ unsigned long get_wchan(struct task_struct *p)
 	if (!p || p == current || p->state==TASK_RUNNING)
 		return 0; 
 	stack = (unsigned long)task_stack_page(p);
-	if (p->thread.sp < stack || p->thread.sp > stack+THREAD_SIZE)
+	if (p->thread.sp < stack || p->thread.sp >= stack+THREAD_SIZE)
 		return 0;
 	fp = *(u64 *)(p->thread.sp);
 	do { 
 		if (fp < (unsigned long)stack ||
-		    fp > (unsigned long)stack+THREAD_SIZE)
+		    fp >= (unsigned long)stack+THREAD_SIZE)
 			return 0; 
 		ip = *(u64 *)(fp+8);
 		if (!in_sched_functions(ip))
--
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