AZL-99434

In the Linux kernel, the following vulnerability has been resolved:

fbdev: serialize mode sysfs access with lockfbinfo()

showmode(), showmodes(), and storemode() access fbinfo->modelist and fbinfo->mode without holding lockfbinfo(). storemodes() takes lockfbinfo() while replacing the modelist and freeing the old one.

A concurrent reader or writer can load a pointer to an old modelist entry before storemodes() frees it, then dereference freed memory or store a stale freed pointer in fbinfo->mode.

Take lockfbinfo() in showmode(), showmodes(), and storemode() to serialize with storemodes(). In showmode(), copy the mode to the stack and format after dropping the lock. In storemode(), split activate() into a locked variant to avoid double-locking, and hold the locks for the modelist walk, mode conversion, activation, and fbinfo->mode assignment together.