[patch 5/13] s390: show_task oops.

[Martin Schwidefsky <schwidefsky@de.ibm.com>]

From: Heiko Carstens <heiko.carstens@de.ibm.com>

[patch 5/13] s390: show_task oops.

The show_task function walks the kernel stack backchain of
processes assuming that the processes are not running. Since
this assumption is not correct walking the backchain can lead
to an addressing exception and therefore to a kernel hang.
So prevent the kernel hang (you still get incorrect results)
verity that all read accesses are within the bounds of the
kernel stack before performing them.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

---

 arch/s390/kernel/process.c |   15 ++++++++++++---
 1 files changed, 12 insertions(+), 3 deletions(-)

diff -urpN linux-2.6/arch/s390/kernel/process.c linux-2.6-patched/arch/s390/kernel/process.c
--- linux-2.6/arch/s390/kernel/process.c	2006-01-12 15:43:19.000000000 +0100
+++ linux-2.6-patched/arch/s390/kernel/process.c	2006-01-12 15:43:55.000000000 +0100
@@ -58,10 +58,19 @@ asmlinkage void ret_from_fork(void) __as
  */
 unsigned long thread_saved_pc(struct task_struct *tsk)
 {
-	struct stack_frame *sf;
+	struct stack_frame *sf, *low, *high;
 
-	sf = (struct stack_frame *) tsk->thread.ksp;
-	sf = (struct stack_frame *) sf->back_chain;
+	if (!tsk || !tsk->thread_info)
+		return 0;
+	low = (struct stack_frame *) tsk->thread_info;
+	high = (struct stack_frame *)
+		((unsigned long) tsk->thread_info + THREAD_SIZE) - 1;
+	sf = (struct stack_frame *) (tsk->thread.ksp & PSW_ADDR_INSN);
+	if (sf <= low || sf > high)
+		return 0;
+	sf = (struct stack_frame *) (sf->back_chain & PSW_ADDR_INSN);
+	if (sf <= low || sf > high)
+		return 0;
 	return sf->gprs[8];
 }
 
-
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