cachefiles: flush all requests after setting CACHEFILES_DEAD

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: cachefiles: flush all requests after setting CACHEFILES_DEAD In ondemand mode, when the daemon is processing an open request, if the kernel flags the cache as CACHEFILES_DEAD, the cachefiles_daemon_write() will always return -EIO, so the daemon can't pass the copen to the kernel. Then the kernel process that is waiting for the copen triggers a hung_task. Since the DEAD state is irreversible, it can only be exited by closing /dev/cachefiles. Therefore, after calling cachefiles_io_error() to mark the cache as CACHEFILES_DEAD, if in ondemand mode, flush all requests to avoid the above hungtask. We may still be able to read some of the cached data before closing the fd of /dev/cachefiles. Note that this relies on the patch that adds reference counting to the req, otherwise it may UAF.

References

• https://git.kernel.org/stable/c/320ba9cbca78be79c912143bbba1d1b35ca55cf0
• https://git.kernel.org/stable/c/3bf0b8030296e9ee60d3d4c15849ad9ac0b47081
• https://git.kernel.org/stable/c/e73fac95084839c5178d97e81c6a2051251bdc00
• https://git.kernel.org/stable/c/85e833cd7243bda7285492b0653c3abb1e2e757b