CVE-2026-98021
UnknownSummary
A vulnerability was found in the Linux kernel's network interface creation and modification mechanism. The IFLA_TXQLEN attribute (txqueuelen) was not properly limited to S16_MAX during netlink parsing, allowing an oversized transmit queue length to be set. This led to excessive memory allocations in pfifo_fast, tun, and tap modules, which could be exploited by an unprivileged user in a namespace.
Risk Assessment
The risk is the possibility of memory exhaustion by an unprivileged user, potentially leading to system crash or denial of service (DoS).
Recommendation
It is recommended to immediately update the Linux kernel to a version containing the fix that enforces the S16_MAX limit on the IFLA_TXQLEN attribute during netlink parsing. Also monitor the availability of patches for your distribution.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: net: reject oversized tx_queue_len at netlink parse time rtnl_create_link() assigns IFLA_TXQLEN directly to dev->tx_queue_len without going through netif_change_tx_queue_len(), so a device created with "ip link add ... txqueuelen 500000" bypasses the S16_MAX cap and still triggers the oversized ring allocations in pfifo_fast, tun and tap. The veth peer nest (rtnl_nla_parse_ifinfomsg()) and the RTM_NEWLINK-on-existing-device path reach the same sinks. Enforce the cap in ifla_policy instead: IFLA_TXQLEN becomes NLA_POLICY_FULL_RANGE(NLA_U32, &txqlen_range) with txqlen_range = { .min = 0, .max = S16_MAX }. All netlink consumers parse against this policy - rtnl_setlink(), rtnl_newlink() (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 RTM_SETLINK half-application wart is gone with it). Document the bound in the rt-link.yaml netlink spec. Conditions to recreate the bug: - CONFIG_NET_SCHED=y, CONFIG_VETH=y, CONFIG_USER_NS=y, CONFIG_NET_NS=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 tx_queue_len that later inflates pfifo_fast/tun/tap ring allocations. - ip link set v0 txqueuelen 500000 is likewise rejected at parse time.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS