CVE-2026-3038: Local DoS and possible privilege escalation via routing sockets

The rtsockmsgbuffer() function serializes routing information into a buffer. As a part of this, it copies sockaddr structures into a sockaddrstorage structure on the stack. It assumes that the source sockaddr length field had already been validated, but this is not necessarily the case, and it's possible for a malicious userspace program to craft a request which triggers a 127-byte overflow.

In practice, this overflow immediately overwrites the canary for the rtsockmsgbuffer() stack frame, resulting in a panic once the function returns.

The bug allows an unprivileged user to crash the kernel by triggering a stack buffer overflow in rtsockmsgbuffer(). In particular, the overflow will corrupt a stack canary value that is verified when the function returns; this mitigates the impact of the stack overflow by triggering a kernel panic.

Other kernel bugs may exist which allow userspace to find the canary value and thus defeat the mitigation, at which point local privilege escalation may be possible.