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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 <tkjos@google.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Todd Kjos 2019-06-12 13:29:27 -07:00 committed by Greg Kroah-Hartman
parent b7108486d2
commit a370003cc3
1 changed files with 14 additions and 2 deletions
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16
drivers/android/binder.c
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@ -1941,8 +1941,18 @@ static void binder_free_txn_fixups(struct binder_transaction *t)
static void binder_free_transaction(struct binder_transaction *t) static void binder_free_transaction(struct binder_transaction *t)
{ {
if (t->buffer) struct binder_proc *target_proc = t->to_proc;
t->buffer->transaction = NULL;
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); binder_free_txn_fixups(t);
kfree(t); kfree(t);
binder_stats_deleted(BINDER_STAT_TRANSACTION); binder_stats_deleted(BINDER_STAT_TRANSACTION);
@ -3551,10 +3561,12 @@ static void binder_transaction(struct binder_proc *proc,
static void static void
binder_free_buf(struct binder_proc *proc, struct binder_buffer *buffer) binder_free_buf(struct binder_proc *proc, struct binder_buffer *buffer)
{ {
binder_inner_proc_lock(proc);
if (buffer->transaction) { if (buffer->transaction) {
buffer->transaction->buffer = NULL; buffer->transaction->buffer = NULL;
buffer->transaction = NULL; buffer->transaction = NULL;
} }
binder_inner_proc_unlock(proc);
if (buffer->async_transaction && buffer->target_node) { if (buffer->async_transaction && buffer->target_node) {
struct binder_node *buf_node; struct binder_node *buf_node;
struct binder_work *w; struct binder_work *w;