This is a note to let you know that I've just added the patch titled
ANDROID: binder: synchronize_rcu() when using POLLFREE.
to my char-misc git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git in the char-misc-linus branch.
The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.
If you have any questions about this process, please let me know.
From 5eeb2ca02a2f6084fc57ae5c244a38baab07033a Mon Sep 17 00:00:00 2001
From: Martijn Coenen maco@android.com Date: Fri, 16 Feb 2018 09:47:15 +0100 Subject: ANDROID: binder: synchronize_rcu() when using POLLFREE.
To prevent races with ep_remove_waitqueue() removing the waitqueue at the same time.
Reported-by: syzbot+a2a3c4909716e271487e@syzkaller.appspotmail.com Signed-off-by: Martijn Coenen maco@android.com Cc: stable stable@vger.kernel.org # 4.14+ Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/android/binder.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c index a85f9033b57e..764b63a5aade 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -4382,6 +4382,15 @@ static int binder_thread_release(struct binder_proc *proc,
binder_inner_proc_unlock(thread->proc);
+ /* + * This is needed to avoid races between wake_up_poll() above and + * and ep_remove_waitqueue() called for other reasons (eg the epoll file + * descriptor being closed); ep_remove_waitqueue() holds an RCU read + * lock, so we can be sure it's done after calling synchronize_rcu(). + */ + if (thread->looper & BINDER_LOOPER_STATE_POLL) + synchronize_rcu(); + if (send_reply) binder_send_failed_reply(send_reply, BR_DEAD_REPLY); binder_release_work(proc, &thread->todo);