[PATCH] x86-64: fix stack bounds checking in get_wchan

[Konstantin Khlebnikov <k.khlebnikov@samsung.com>]

This patch fixes potential oops on unwinding volatile stack. get_wchan() is
lockless, task may wake up at any time and override any frame under us.
Stackframe is 16 bytes long plus it's supposed to be 64bit aligned.

Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@samsung.com>
---
 arch/x86/kernel/process_64.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 9c0280f..a7f089d 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -442,12 +442,11 @@ 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 - 8)
 		return 0;
 	fp = *(u64 *)(p->thread.sp);
 	do {
-		if (fp < (unsigned long)stack ||
-		    fp >= (unsigned long)stack+THREAD_SIZE)
+		if (fp < stack || fp > stack + THREAD_SIZE - 16 || fp & 7)
 			return 0;
 		ip = *(u64 *)(fp+8);
 		if (!in_sched_functions(ip))