x86: Pin task-stack in __get_wchan()

When commit 5d1ceb3969b6 ("x86: Fix __get_wchan() for !STACKTRACE")
moved from stacktrace to native unwind_*() usage, the
try_get_task_stack() got lost, leading to use-after-free issues for
dying tasks.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Fixes: 5d1ceb3969b6 ("x86: Fix __get_wchan() for !STACKTRACE")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=215031
Link: https://lore.kernel.org/stable/YZV02RCRVHIa144u@fedora64.linuxtx.org/
Reported-by: Justin Forbes <jmforbes@linuxtx.org>
Reported-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index e9ee8b5..04143a6 100644 (file)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -964,6 +964,9 @@ unsigned long __get_wchan(struct task_struct *p)
        struct unwind_state state;
        unsigned long addr = 0;
 
+       if (!try_get_task_stack(p))
+               return 0;
+
        for (unwind_start(&state, p, NULL, NULL); !unwind_done(&state);
             unwind_next_frame(&state)) {
                addr = unwind_get_return_address(&state);
@@ -974,6 +977,8 @@ unsigned long __get_wchan(struct task_struct *p)
                break;
        }
 
+       put_task_stack(p);
+
        return addr;
 }