CVE-2026-31696rxrpc: Fix missing validation of ticket length in non-XDR key preparsing

Official description

In the Linux kernel, the following vulnerability has been resolved: rxrpc: Fix missing validation of ticket length in non-XDR key preparsing In rxrpc_preparse(), there are two paths for parsing key payloads: the XDR path (for large payloads) and the non-XDR path (for payloads <= 28 bytes). While the XDR path (rxrpc_preparse_xdr_rxkad()) correctly validates the ticket length against AFSTOKEN_RK_TIX_MAX, the non-XDR path fails to do so. This allows an unprivileged user to provide a very large ticket length. When this key is later read via rxrpc_read(), the total token size (toksize) calculation results in a value that exceeds AFSTOKEN_LENGTH_MAX, triggering a WARN_ON(). [ 2001.302904] WARNING: CPU: 2 PID: 2108 at net/rxrpc/key.c:778 rxrpc_read+0x109/0x5c0 [rxrpc] Fix this by adding a check in the non-XDR parsing path of rxrpc_preparse() to ensure the ticket length does not exceed AFSTOKEN_RK_TIX_MAX, bringing it into parity with the XDR parsing logic.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/44714dfda386884919ba366411880b6fb3c3efd3
• https://git.kernel.org/stable/c/41a117dd80371343babc52198d1114e83eb37627
• https://git.kernel.org/stable/c/9a397aa9b5e53ca63d4d6aefb542832eca389618
• https://git.kernel.org/stable/c/1fa36cf495b0023e8475d038535c05e4063211e1
• https://git.kernel.org/stable/c/4458757c020592a3094366e0fb20457383b42f92
• https://git.kernel.org/stable/c/ce383ba615339f8eaec646a166d2c2b015bb5ca0
• https://git.kernel.org/stable/c/a1be1c9ece26cea69654f28b255ff9a7906b897b
• https://git.kernel.org/stable/c/ac33733b10b484d666f97688561670afd5861383
• https://cert-portal.siemens.com/productcert/html/ssa-784472.html