[PATCH 0/2] Xen Security Advisory 371 v3 (CVE-2021-28688) - Linux: blkback driver may leak persistent grants

[Tim Gardner]

H/G/F/X are clean cherry-picks. Look at Bionic closely to make sure I got the backport correct
as the code is a bit different.

[SRU Justification]

See [XSA 371](http://xenbits.xen.org/xsa/advisory-371.html). commit
871997bc9e423f05c7da7c9178e62dde5df2a7f8 ("xen-blkback: fix error handling in
xen_blkbk_map()") introduced a security vulnerability.

Original Commit:
871997bc9e423f05c7da7c9178e62dde5df2a7f8 ("xen-blkback: fix error handling in xen_blkbk_map()")

New commit with security fix:
a846738f8c3788d846ed1f587270d2f2e3d32432 ("xen-blkback: don't leak persistent grants from xen_blkbk_map()")

[Test Plan]
none

[Where problems could occur]
Unknown

[Other Info]
- http://xenbits.xen.org/xsa/advisory-371.html
- http://xenbits.xen.org/xsa/xsa371-linux.patch
- http://xenbits.xen.org/xsa/advisory-365.html
- http://xenbits.xen.org/xsa/xsa365-linux.patch