Description: f2fs: fix UAF in f2fs_available_free_memory
References:
 https://source.android.com/security/bulletin/pixel/2022-06-01
Notes:
 bwh> Actually introduced in 5.13, not fixed, by the first
 bwh> referenced commit d6d2b491a82e "f2fs: allow to change discard
 bwh> policy based on cached discard cmds".
Bugs:
upstream: released (5.16-rc1) [5429c9dbc9025f9a166f64e22e3a69c94fd5b29b]
5.10-upstream-stable: N/A "Vulnerability introduced later"
4.19-upstream-stable: N/A "Vulnerability introduced later"
4.9-upstream-stable: N/A "Vulnerability introduced later"
sid: released (5.15.3-1)
5.10-bullseye-security: N/A "Vulnerability introduced later"
4.19-buster-security: N/A "Vulnerability introduced later"
4.9-stretch-security: N/A "Vulnerability introduced later"