Description: nbd_genl_status: null check for nla_nest_start
References:
 https://lore.kernel.org/patchwork/patch/1106884/
 https://lore.kernel.org/patchwork/patch/1126650/
Notes:
 bwh> Introduced in 4.12 by commit 47d902b90a32 "nbd: add a status netlink
 bwh> command".  Probably not exploitable in most configurations.
Bugs:
upstream: needed
6.1-upstream-stable: needed
5.10-upstream-stable: needed
4.19-upstream-stable: needed
4.9-upstream-stable: N/A "Vulnerable code not present"
3.16-upstream-stable: N/A "Vulnerable code not present"
sid: needed
6.1-bookworm-security: needed
5.10-bullseye-security: needed
4.19-buster-security: needed
4.9-stretch-security: N/A "Vulnerable code not present"
3.16-jessie-security: N/A "Vulnerable code not present"