UBUNTU-CVE-2026-98021: Medium severity ubuntu/linux vulnerability

In the Linux kernel, the following vulnerability has been resolved: net: reject oversized txqueuelen at netlink parse time rtnlcreatelink() assigns IFLATXQLEN directly to dev->txqueuelen without going through netifchangetxqueuelen(), so a device created with "ip link add ... txqueuelen 500000" bypasses the S16MAX cap and still triggers the oversized ring allocations in pfifofast, tun and tap. The veth peer nest (rtnlnlaparseifinfomsg()) and the RTMNEWLINK-on-existing-device path reach the same sinks. Enforce the cap in iflapolicy instead: IFLATXQLEN becomes NLAPOLICYFULLRANGE(NLAU32, &txqlenrange) with txqlenrange = { .min = 0, .max = S16MAX }. All netlink consumers parse against this policy - rtnlsetlink(), rtnlnewlink() (create and change), and the veth peer nest - so every netlink path is capped at parse time and rejects the attribute with -ERANGE plus a proper "integer out of range" extack message before any device state is modified (the RTMSETLINK half-application wart is gone with it). Document the bound in the rt-link.yaml netlink spec. Conditions to recreate the bug: - CONFIGNETSCHED=y, CONFIGVETH=y, CONFIGUSERNS=y, CONFIGNETNS=y. - Unprivileged user in a fresh user+net namespace (unshare -Urn): ip link add v0 txqueuelen 500000 type veth peer name v1 -> on the fixed kernel this is rejected with -ERANGE ("integer out of range" extack) instead of installing an oversized txqueuelen that later inflates pfifofast/tun/tap ring allocations. - ip link set v0 txqueuelen 500000 is likewise rejected at parse time.