A locking inconsistency issue was discovered in the tty subsystem of the
Linux kernel through 5.9.13. drivers/tty/tty_io.c and
drivers/tty/tty_jobctrl.c may allow a read-after-free attack against
TIOCGSID, aka CID-c8bcd9c5be24.

Jann Horn discovered that the tty subsystem of the Linux kernel did not use
consistent locking in some situations, leading to a read-after-free
vulnerability. A local attacker could use this to cause a denial of service
(system crash) or possibly expose sensitive information (kernel memory).