This is a note to let you know that I've just added the patch titled
binder: fix possible UAF when freeing buffer
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 a370003cc301d4361bae20c9ef615f89bf8d1e8a Mon Sep 17 00:00:00 2001
From: Todd Kjos <tkjos@xxxxxxxxxxx>
Date: Wed, 12 Jun 2019 13:29:27 -0700
Subject: 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@xxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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 @@ static void binder_transaction(struct binder_proc *proc,
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;
--
2.22.0
