Jason A. Donenfeld, the author of the WireGuard VPN, brought to the developers' attention a dirty hack present in the Linux kernel code, altering the behavior for processes whose names begin with the character 'X'. At first glance, such fixes are typically applied in rootkits to leave a hidden backdoor tied to the process, but an investigation revealed that the change was added in 2019 to temporarily resolve a surfaced compatibility violation with user space, in accordance with the principle that changes in the kernel should not break compatibility with applications.
Problems occurred when attempting to use the atomic mode change mechanism in the xf86-video-modesetting DDX driver used in the X.Org server, which was linked to processes starting with the character 'X' (it was implied that the workaround applied to the 'Xorg' process). Almost immediately, the issue in X.Org was resolved (the use of the atomic API was disabled by default), but the temporary fix was forgotten to be removed from the kernel, and attempts to send an ioctl for atomic mode changes for all processes beginning with the character 'X' still continue to result in the error being returned. if (current->comm[0] == 'X' && req->value == 1) { pr_info("broken atomic modeset userspace detected, disabling atomic\n"); return -EOPNOTSUPP; }
Source: opennet.ru
