Description: blkback driver may leak persistent grants
References:
 https://xenbits.xen.org/xsa/advisory-371.html
Notes:
 carnil> Issue introduced with the fix for XSA-365 which was included in
 carnil> 5.12-rc1 and then backported to 5.10.18, 4.19.177 and 4.9.258.
Bugs:
upstream: released (5.12-rc6) [a846738f8c3788d846ed1f587270d2f2e3d32432]
5.10-upstream-stable: released (5.10.27) [3a1ca9bd4f5a647439e82e07b03d072781d9d180]
4.19-upstream-stable: released (4.19.184) [16356ddb587867c2a5ab85407eeb75f2b8818207]
4.9-upstream-stable: released (4.9.264) [3cb86952ce3c8b28a0c1f3ce82848618d8628015]
sid: released (5.10.28-1)
4.19-buster-security: released (4.19.194-1)
4.9-stretch-security: released (4.9.272-1)