[PATCH 0/1 v2][Bionic] Xen Security Advisory 371 v3 (CVE-2021-28688) - Linux: blkback driver may leak persistent grants

[Tim Gardner]

v2 - Fix commit a846738f8c3788d846ed1f587270d2f2e3d32432 ("xen-blkback: don't
leak persistent grants from xen_blkbk_map()") is now a clean cherry-pick after
the application of stable patches from "UBUNTU: upstream stable to v4.14.225,
v4.19.180" to bionic:linux-master-next.

[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]
Released in stable kernels:
linux-4.14.y
linux-4.19.y
linux-4.4.y
linux-4.9.y
linux-5.10.y
linux-5.11.y
linux-5.4.y

[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