[PATCH v2] stacktrace: check whether task has a stack before saving it

[Ronald Wahl <rwahl@gmx.de>]

From: Ronald Wahl <ronald.wahl@raritan.com>

I encountered a crash on ARM32 when trying to dump the stack of some
zombie process. This is caused by a missing check whether the task
actually has a valid stack. This commit adds this check.

Commit 214d8ca6ee85 ("stacktrace: Provide common infrastructure")
introduced this check for platforms that define CONFIG_ARCH_STACKWALK
but ARM32 is not one of them.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-arch@vger.kernel.org
Signed-off-by: Ronald Wahl <ronald.wahl@raritan.com>
---
V2: - added missing put_task_stack(task) to avoid memory leak

 kernel/stacktrace.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 9ed5ce989415..0bb67bd633c6 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -298,7 +298,11 @@ unsigned int stack_trace_save_tsk(struct task_struct *task,
 		.skip	= skipnr + (current == task),
 	};

+	if (!try_get_task_stack(task))
+		return 0;
+
 	save_stack_trace_tsk(task, &trace);
+	put_task_stack(task);
 	return trace.nr_entries;
 }

--
2.43.0