CVE-2026-89540

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

sunrpc: init gssp_lock before publishing proc entry

create_use_gss_proxy_proc_entry() publishes /proc/net/rpc/use-gss-proxy

via proc_create_data() before init_gssp_clnt() runs mutex_init() on

sn->gssp_lock. Once the dentry is linked under proc_subdir_lock it is

immediately reachable from userspace, so a write that lands in the

window drives set_gssp_clnt() into mutex_lock() on a zero-initialized

struct mutex.

create_use_gss_proxy_proc_entry(net)

proc_create_data("use-gss-proxy", ...) /* dentry live */

init_gssp_clnt(sn)

mutex_init(&sn->gssp_lock) /* too late */

write_gssp()

set_gssp_clnt(net)

mutex_lock(&sn->gssp_lock) /* uninitialized */

gssp_rpc_create(...)

sn->gssp_clnt = clnt

mutex_unlock(&sn->gssp_lock)

The window spans only the two statements between proc_create_data()

returning and init_gssp_clnt(), so a writer reaches it only if the

registering thread is preempted there while another task is already

opening the freshly published file. register_pernet_subsys() runs in

preemptible context under pernet_ops_rwsem, so that preemption is

possible, and the window widens on auth_rpcgss module load, when the

proc entry is created for every live net namespace whose tasks are

already running. A writer that wins the race locks a zero-filled

struct mutex. On CONFIG_DEBUG_MUTEXES the missing magic value trips a

"lock used without init" splat; on a production kernel the fast path

acquires the lock via CMPXCHG(owner, 0, current). In the latter case

a second writer that arrives before init_gssp_clnt() re-zeroes owner

can enter set_gssp_clnt() concurrently, shut down the first writer's

clnt while it is still in use, and leak the loser's clnt.

Fix by initializing sn->gssp_lock in sunrpc_init_net() so its lifetime

matches the sunrpc_net it lives in. sn->gssp_clnt is already NULL from

the kzalloc that backs net_generic storage, so the lazy helper is no

longer needed; drop init_gssp_clnt(), its prototype, and the call from

create_use_gss_proxy_proc_entry(). sunrpc.ko is a build-time

dependency of auth_rpcgss.ko, so sunrpc_init_net() has always run on

every netns before any auth_gss pernet init can publish the proc

entry.