CVE-2021-26930

An issue was discovered in the Linux kernel 3.11 through 5.10.16, as used
by Xen. To service requests to the PV backend, the driver maps grant
references provided by the frontend. In this process, errors may be
encountered. In one case, an error encountered earlier might be discarded
by later processing, resulting in the caller assuming successful mapping,
and hence subsequent operations trying to access space that wasn’t mapped.
In another case, internal state would be insufficiently updated, preventing
safe recovery from the error. This affects
drivers/block/xen-blkback/blkback.c.