[PATCH] binder: fix memory leak of spamming work

[Carlos Llamas <cmllamas@google.com>]

A transaction complete work is allocated and queued for each
transaction. Under certain conditions the work->type might be marked as
BINDER_WORK_TRANSACTION_ONEWAY_SPAM_SUSPECT to notify userspace about
potential spamming threads.

However, this work->type is not being handled in binder_release_work()
so it will leak during a clean up. This was reported by syzkaller with
the following kmemleak dump:

BUG: memory leak
unreferenced object 0xffff88810e2d6de0 (size 32):
  comm "syz-executor338", pid 5046, jiffies 4294968230 (age 13.590s)
  hex dump (first 32 bytes):
    e0 6d 2d 0e 81 88 ff ff e0 6d 2d 0e 81 88 ff ff  .m-......m-.....
    04 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffff81573b75>] kmalloc_trace+0x25/0x90 mm/slab_common.c:1114
    [<ffffffff83d41873>] kmalloc include/linux/slab.h:599 [inline]
    [<ffffffff83d41873>] kzalloc include/linux/slab.h:720 [inline]
    [<ffffffff83d41873>] binder_transaction+0x573/0x4050 drivers/android/binder.c:3152
    [<ffffffff83d45a05>] binder_thread_write+0x6b5/0x1860 drivers/android/binder.c:4010
    [<ffffffff83d486dc>] binder_ioctl_write_read drivers/android/binder.c:5066 [inline]
    [<ffffffff83d486dc>] binder_ioctl+0x1b2c/0x3cf0 drivers/android/binder.c:5352
    [<ffffffff816b25f2>] vfs_ioctl fs/ioctl.c:51 [inline]
    [<ffffffff816b25f2>] __do_sys_ioctl fs/ioctl.c:871 [inline]
    [<ffffffff816b25f2>] __se_sys_ioctl fs/ioctl.c:857 [inline]
    [<ffffffff816b25f2>] __x64_sys_ioctl+0xf2/0x140 fs/ioctl.c:857
    [<ffffffff84b30008>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
    [<ffffffff84b30008>] do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
    [<ffffffff84c0008b>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fix the leak by kfreeing this work in binder_release_work().

Cc: stable@vger.kernel.org
Fixes: a7dc1e6f99df ("binder: tell userspace to dump current backtrace when detected oneway spamming")
Reported-by: syzbot+7f10c1653e35933c0f1e@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7f10c1653e35933c0f1e
Signed-off-by: Carlos Llamas <cmllamas@google.com>
---
 drivers/android/binder.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 367afac5f1bf..d7aa561f4ef2 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -4831,6 +4831,9 @@ static void binder_release_work(struct binder_proc *proc,
 		} break;
 		case BINDER_WORK_NODE:
 			break;
+		case BINDER_WORK_TRANSACTION_ONEWAY_SPAM_SUSPECT:
+			kfree(w);
+			break;
 		default:
 			pr_err("unexpected work type, %d, not freed\n",
 			       wtype);
-- 
2.42.0.515.g380fc7ccd1-goog