CVE-2021-46935 Information

Description

In the Linux kernel the following vulnerability has been resolved:

binder: fix async_free_space accounting for empty parcels

In 4.13 commit 74310e06be4d (ndroid: 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 ree\ 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 uffer_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.

Reference

https://git.kernel.org/stable/c/2d2df539d05205fd83c404d5f2dff48d36f9b495 https://git.kernel.org/stable/c/7c7064402609aeb6fb11be1b4ec10673ff17b593 https://git.kernel.org/stable/c/103b16a8c51f96d5fe063022869ea906c256e5da https://git.kernel.org/stable/c/1cb8444f3114f0bb2f6e3bcadcf09aa4a28425d4 https://git.kernel.org/stable/c/17691bada6b2f1d5f1c0f6d28cd9d0727023b0ff https://git.kernel.org/stable/c/cfd0d84ba28c18b531648c9d4a35ecca89ad9901