[PATCH] Uprobes: Fix kernel oops with delayed_uprobe_remove()

[Ravi Bangoria]

syzbot reported a kernel crash with delayed_uprobe_remove():
  https://lkml.org/lkml/2018/11/1/1244

Backtrace mentioned in the link points to a race between process
exit and uprobe_unregister(). Fix it by locking delayed_uprobe_lock
before calling delayed_uprobe_remove() from put_uprobe().

Reported-by: syzbot+cb1fb754b771caca0...@syzkaller.appspotmail.com
Signed-off-by: Ravi Bangoria <ravi.bango...@linux.ibm.com>
---
 kernel/events/uprobes.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 96fb51f3994f..e527c4753d4f 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -572,7 +572,9 @@ static void put_uprobe(struct uprobe *uprobe)
                 * gets called, we don't get a chance to remove uprobe from
                 * delayed_uprobe_list from remove_breakpoint(). Do it here.
                 */
+               mutex_lock(&delayed_uprobe_lock);
                delayed_uprobe_remove(uprobe, NULL);
+               mutex_unlock(&delayed_uprobe_lock);
                kfree(uprobe);
        }
 }
-- 
2.19.1