Description: Incorrect updates of uninstantiated keys crash the kernel
References:
 https://bugzilla.redhat.com/show_bug.cgi?id=1498016
 https://marc.info/?t=150654188100001&r=1&w=2
 https://marc.info/?t=150783958600011&r=1&w=2
Notes:
 carnil> The bug is not restricted to CONFIG_ENCRYPTED_KEYS=y
 carnil> only, but the impact is different. As noted in the commit
 carnil> message: "In the case of the "user" and "logon" key types
 carnil> this causes a memory leak, at best.  Maybe even worse, the
 carnil> ->update() methods of the "encrypted" and "trusted" key types
 carnil> actually just dereference a NULL pointer when passed an
 carnil> uninstantiated key.
 carnil> For 4.13.x fixed in 4.13.10 with 24a33a0c96f3e976c18e4321ca09f71cb835a9b5
Bugs:
upstream: released (4.14-rc6) [60ff5b2f547af3828aebafd54daded44cfb0807a]
4.9-upstream-stable: released (4.9.59) [da0c7503c0b886784bf8bcb279c7d71c1e50c438]
3.16-upstream-stable: released (3.16.50) [24832178de3ab7b6fb42f2730d8d675e3d30adb2]
3.2-upstream-stable: released (3.2.95) [57f94e88bb255bf7b7d267c999aefbe4557307c1]
sid: released (4.13.10-1)
4.9-stretch-security: released (4.9.65-1)
3.16-jessie-security: released (3.16.51-1)
3.2-wheezy-security: released (3.2.96-1)