A local user can trigger a flaw in the Linux kernel's handling of key lookups in the keychain subsystem.

The keyrejectandlink() function contains an error in which a key-lookup can fail and in an attempt to cache the failed lookup may attempt to free memory which can still be in use.

This could crash the system or at worse free a memory block which would then be re-used by another kernel mechanism causing a user after free.

Product bug:

https://bugzilla.redhat.com/showbug.cgi?id=1341352

Upstream patch:

https://www.spinics.net/lists/linux-kernel-janitors/msg26069.html