CVE-2024-40913 Information

Description

In the Linux kernel the following vulnerability has been resolved:

cachefiles: defer exposing anon_fd until after copy_to_user() succeeds

After installing the anonymous fd we can now see it in userland and close it. However at this point we may not have gotten the reference count of the cache but we will put it during colse fd so this may cause a cache UAF.

So grab the cache reference count before fd_install(). In addition by kernel convention fd is taken over by the user land after fd_install() and the kernel should not call close_fd() after that i.e. it should call fd_install() after everything is ready thus fd_install() is called after copy_to_user() succeeds.

Reference

https://git.kernel.org/stable/c/eac51d9daacd61dcc93333ff6a890cf3efc8c1c0 https://git.kernel.org/stable/c/d2d3eb377a5d081bf2bed177d354a4f59b74da88 https://git.kernel.org/stable/c/b9f58cdae6a364a3270fd6b6a46e0fd4f7f8ce32 https://git.kernel.org/stable/c/4b4391e77a6bf24cba2ef1590e113d9b73b11039