This is a note to let you know that I've just added the patch titled binder: fix async_free_space accounting for empty parcels to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: binder-fix-async_free_space-accounting-for-empty-parcels.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From cfd0d84ba28c18b531648c9d4a35ecca89ad9901 Mon Sep 17 00:00:00 2001 From: Todd Kjos <tkjos@xxxxxxxxxx> Date: Mon, 20 Dec 2021 11:01:50 -0800 Subject: binder: fix async_free_space accounting for empty parcels From: Todd Kjos <tkjos@xxxxxxxxxx> commit cfd0d84ba28c18b531648c9d4a35ecca89ad9901 upstream. In 4.13, commit 74310e06be4d ("android: binder: Move buffer out of area shared with user space") fixed a kernel structure visibility issue. As part of that patch, sizeof(void *) was used as the buffer size for 0-length data payloads so the driver could detect abusive clients sending 0-length asynchronous transactions to a server by enforcing limits on async_free_size. Unfortunately, on the "free" side, the accounting of async_free_space did not add the sizeof(void *) back. The result was that up to 8-bytes of async_free_space were leaked on every async transaction of 8-bytes or less. These small transactions are uncommon, so this accounting issue has gone undetected for several years. The fix is to use "buffer_size" (the allocated buffer size) instead of "size" (the logical buffer size) when updating the async_free_space during the free operation. These are the same except for this corner case of asynchronous transactions with payloads < 8 bytes. Fixes: 74310e06be4d ("android: binder: Move buffer out of area shared with user space") Signed-off-by: Todd Kjos <tkjos@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx # 4.14+ Link: https://lore.kernel.org/r/20211220190150.2107077-1-tkjos@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/android/binder_alloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -630,7 +630,7 @@ static void binder_free_buf_locked(struc BUG_ON(buffer->data > alloc->buffer + alloc->buffer_size); if (buffer->async_transaction) { - alloc->free_async_space += size + sizeof(struct binder_buffer); + alloc->free_async_space += buffer_size + sizeof(struct binder_buffer); binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC_ASYNC, "%d: binder_free_buf size %zd async free %zd\n", Patches currently in stable-queue which might be from tkjos@xxxxxxxxxx are queue-4.19/binder-fix-async_free_space-accounting-for-empty-parcels.patch