xen: privcmd: Fix possible access to a freed kirqfd instance

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: xen: privcmd: Fix possible access to a freed kirqfd instance Nothing prevents simultaneous ioctl calls to privcmd_irqfd_assign() and privcmd_irqfd_deassign(). If that happens, it is possible that a kirqfd created and added to the irqfds_list by privcmd_irqfd_assign() may get removed by another thread executing privcmd_irqfd_deassign(), while the former is still using it after dropping the locks. This can lead to a situation where an already freed kirqfd instance may be accessed and cause kernel oops. Use SRCU locking to prevent the same, as is done for the KVM implementation for irqfds.

References

• https://git.kernel.org/stable/c/e997b357b13a7d95de31681fc54fcc34235fa527
• https://git.kernel.org/stable/c/112fd2f02b308564724b8e81006c254d20945c4b
• https://git.kernel.org/stable/c/611ff1b1ae989a7bcce3e2a8e132ee30e968c557