[PATCH 3.16 246/410] binder: check for binder_thread allocation failure in binder_poll()

[Ben Hutchings]

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@xxxxxxxxxx>

commit f88982679f54f75daa5b8eff3da72508f1e7422f upstream.

If the kzalloc() in binder_get_thread() fails, binder_poll()
dereferences the resulting NULL pointer.

Fix it by returning POLLERR if the memory allocation failed.

This bug was found by syzkaller using fault injection.

Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Fixes: 457b9a6f09f0 ("Staging: android: add binder driver")
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.16:
 - Drop the binder global lock before returning
 - Adjust filename]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/drivers/staging/android/binder.c
+++ b/drivers/staging/android/binder.c
@@ -2572,6 +2572,10 @@ static unsigned int binder_poll(struct f
 	binder_lock(__func__);
 
 	thread = binder_get_thread(proc);
+	if (!thread) {
+		binder_unlock(__func__);
+		return POLLERR;
+	}
 
 	wait_for_proc_work = thread->transaction_stack == NULL &&
 		list_empty(&thread->todo) && thread->return_error == BR_OK;