Description: l2tp: protect sock pointer of struct pppol2tp_session with RCU
References:
 https://source.android.com/security/bulletin/pixel/2021-03-01
Notes:
 carnil> was as well part of the bigger fixes in CVE-2020-27067.
Bugs:
upstream: released (4.15-rc1) [ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741]
5.10-upstream-stable: N/A "Fixed before branching point"
4.19-upstream-stable: N/A "Fixed before branching point"
4.9-upstream-stable: released (4.9.225) [5803ecd7f6ac6f747582e775caa62ac9d0489261]
sid: released (4.15.4-1)
4.19-buster-security: N/A "Fixed before branching point"
4.9-stretch-security: released (4.9.228-1)