linux-kernel - [PATCH 08/12] x86/dumpstack: Pin the target stack in save_stack_trace

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Date:   Tue, 13 Sep 2016 14:29:28 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org
Cc:     Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        Brian Gerst <brgerst@...il.com>, Jann Horn <jann@...jh.net>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH 08/12] x86/dumpstack: Pin the target stack in save_stack_trace_tsk()

This will prevent a crash if the target task dies before or while
dumping its stack once we start freeing task stacks early.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/kernel/stacktrace.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 4738f5e0f2ab..b3f32fbe3ba4 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -79,9 +79,14 @@ void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
 
 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 {
+	if (!try_get_task_stack(tsk))
+		return;
+
 	dump_trace(tsk, NULL, NULL, 0, &save_stack_ops_nosched, trace);
 	if (trace->nr_entries < trace->max_entries)
 		trace->entries[trace->nr_entries++] = ULONG_MAX;
+
+	put_task_stack(tsk);
 }
 EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
 
-- 
2.7.4