On Mon, Dec 20, 2021 at 11:06:09AM -0800, Todd Kjos wrote:
On Mon, Dec 20, 2021 at 11:02 AM Todd Kjos tkjos@google.com wrote:
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
I forgot to CC stable. This applies to all stable branches back to 4.14. Cc: stable@vger.kernel.org # 4.14+
Thanks, I've added that to the patch when committing it.
greg k-h