CVE-2025-39962

In the Linux kernel, the following vulnerability has been resolved:

rxrpc: Fix untrusted unsigned subtract

Fix the following Smatch static checker warning:

net/rxrpc/rxgk_app.c:65 rxgk_yfs_decode_ticket() warn: untrusted unsigned subtract. 'ticket_len - 10 * 4'

by prechecking the length of what we're trying to extract in two places in the token and decoding for a response packet.

Also use sizeof() on the struct we're extracting rather specifying the size numerically to be consistent with the other related statements.

This vulnerability does not affect Red Hat Enterprise Linux because the vulnerable RxRPC code is not present in supported kernels. The underlying flaw involves an unchecked arithmetic subtraction during ticket decoding that could lead to an underflow and unexpected behavior when processing untrusted packets. Because this functionality was introduced in a newer upstream kernel release, supported Red Hat kernel versions are not impacted.