Description: speakup: Reject setting the speakup line discipline outside of speakup
References:
 https://www.openwall.com/lists/oss-security/2020/12/07/1
Notes:
 carnil> Fixed as well in v5.9.14.
 bwh> Introduced in 4.13 by commit 1ab92da32e37 "staging: speakup: add
 bwh> tty-based comms functions".
Bugs:
upstream: released (5.10-rc7) [f0992098cadb4c9c6a00703b66cafe604e178fea]
5.10-upstream-stable: N/A "Fixed before branch point"
4.19-upstream-stable: released (4.19.163) [de867367f35237729e285ff6efa3fd4e4b0b9008]
4.9-upstream-stable: N/A "Vulnerability introduced later"
sid: released (5.9.15-1)
4.19-buster-security: released (4.19.171-1)
4.9-stretch-security: N/A "Vulnerability introduced later"