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Subject[PATCH 4.19 001/114] s390/process: avoid potential reading of freed stack
Date
From: Vasily Gorbik <gor@linux.ibm.com>

commit 8769f610fe6d473e5e8e221709c3ac402037da6c upstream.

With THREAD_INFO_IN_TASK (which is selected on s390) task's stack usage
is refcounted and should always be protected by get/put when touching
other task's stack to avoid race conditions with task's destruction code.

Fixes: d5c352cdd022 ("s390: move thread_info into task_struct")
Cc: stable@vger.kernel.org # v4.10+
Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/s390/kernel/process.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)

--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -183,20 +183,30 @@ unsigned long get_wchan(struct task_stru

if (!p || p == current || p->state == TASK_RUNNING || !task_stack_page(p))
return 0;
+
+ if (!try_get_task_stack(p))
+ return 0;
+
low = task_stack_page(p);
high = (struct stack_frame *) task_pt_regs(p);
sf = (struct stack_frame *) p->thread.ksp;
- if (sf <= low || sf > high)
- return 0;
+ if (sf <= low || sf > high) {
+ return_address = 0;
+ goto out;
+ }
for (count = 0; count < 16; count++) {
sf = (struct stack_frame *) sf->back_chain;
- if (sf <= low || sf > high)
- return 0;
+ if (sf <= low || sf > high) {
+ return_address = 0;
+ goto out;
+ }
return_address = sf->gprs[8];
if (!in_sched_functions(return_address))
- return return_address;
+ goto out;
}
- return 0;
+out:
+ put_task_stack(p);
+ return return_address;
}

unsigned long arch_align_stack(unsigned long sp)

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