From: Todd Kjos tkjos@google.com
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@google.com Cc: stable@vger.kernel.org # 4.14+ Link: https://lore.kernel.org/r/20211220190150.2107077-1-tkjos@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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",