From a370003cc301d4361bae20c9ef615f89bf8d1e8a Mon Sep 17 00:00:00 2001 From: Todd Kjos Date: Wed, 12 Jun 2019 13:29:27 -0700 Subject: [PATCH] binder: fix possible UAF when freeing buffer There is a race between the binder driver cleaning up a completed transaction via binder_free_transaction() and a user calling binder_ioctl(BC_FREE_BUFFER) to release a buffer. It doesn't matter which is first but they need to be protected against running concurrently which can result in a UAF. Signed-off-by: Todd Kjos Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 748ac489ef7e..bc26b5511f0a 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -1941,8 +1941,18 @@ static void binder_free_txn_fixups(struct binder_transaction *t) static void binder_free_transaction(struct binder_transaction *t) { - if (t->buffer) - t->buffer->transaction = NULL; + struct binder_proc *target_proc = t->to_proc; + + if (target_proc) { + binder_inner_proc_lock(target_proc); + if (t->buffer) + t->buffer->transaction = NULL; + binder_inner_proc_unlock(target_proc); + } + /* + * If the transaction has no target_proc, then + * t->buffer->transaction has already been cleared. + */ binder_free_txn_fixups(t); kfree(t); binder_stats_deleted(BINDER_STAT_TRANSACTION); @@ -3551,10 +3561,12 @@ err_invalid_target_handle: static void binder_free_buf(struct binder_proc *proc, struct binder_buffer *buffer) { + binder_inner_proc_lock(proc); if (buffer->transaction) { buffer->transaction->buffer = NULL; buffer->transaction = NULL; } + binder_inner_proc_unlock(proc); if (buffer->async_transaction && buffer->target_node) { struct binder_node *buf_node; struct binder_work *w; -- 2.30.2