From 5ce1ed6159731a41fdd0b03eedbed4e147036a5a Mon Sep 17 00:00:00 2001 From: Chris Mason Date: Sat, 30 May 2026 20:42:52 -0400 Subject: [PATCH] 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. Fixes: 030d794bf498 ("SUNRPC: Use gssproxy upcall for server RPCGSS authentication.") Cc: stable@vger.kernel.org Assisted-by: kres:claude-opus-4-7 Signed-off-by: Chris Mason Reviewed-by: Jeff Layton Link: https://patch.msgid.link/20260530-tier2-local-v2-1-5a0fd532db57@oracle.com Signed-off-by: Chuck Lever --- net/sunrpc/auth_gss/gss_rpc_upcall.c | 6 ------ net/sunrpc/auth_gss/gss_rpc_upcall.h | 1 - net/sunrpc/auth_gss/svcauth_gss.c | 1 - net/sunrpc/sunrpc_syms.c | 1 + 4 files changed, 1 insertion(+), 8 deletions(-) diff --git a/net/sunrpc/auth_gss/gss_rpc_upcall.c b/net/sunrpc/auth_gss/gss_rpc_upcall.c index 0fa4778620d9..b7f70b1adb18 100644 --- a/net/sunrpc/auth_gss/gss_rpc_upcall.c +++ b/net/sunrpc/auth_gss/gss_rpc_upcall.c @@ -121,12 +121,6 @@ static int gssp_rpc_create(struct net *net, struct rpc_clnt **_clnt) return result; } -void init_gssp_clnt(struct sunrpc_net *sn) -{ - mutex_init(&sn->gssp_lock); - sn->gssp_clnt = NULL; -} - int set_gssp_clnt(struct net *net) { struct sunrpc_net *sn = net_generic(net, sunrpc_net_id); diff --git a/net/sunrpc/auth_gss/gss_rpc_upcall.h b/net/sunrpc/auth_gss/gss_rpc_upcall.h index 31e96344167e..b3c2b2b90798 100644 --- a/net/sunrpc/auth_gss/gss_rpc_upcall.h +++ b/net/sunrpc/auth_gss/gss_rpc_upcall.h @@ -29,7 +29,6 @@ int gssp_accept_sec_context_upcall(struct net *net, struct gssp_upcall_data *data); void gssp_free_upcall_data(struct gssp_upcall_data *data); -void init_gssp_clnt(struct sunrpc_net *); int set_gssp_clnt(struct net *); void clear_gssp_clnt(struct sunrpc_net *); diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c index 764b4d82951d..967e9d53080d 100644 --- a/net/sunrpc/auth_gss/svcauth_gss.c +++ b/net/sunrpc/auth_gss/svcauth_gss.c @@ -1468,7 +1468,6 @@ static int create_use_gss_proxy_proc_entry(struct net *net) &use_gss_proxy_proc_ops, net); if (!*p) return -ENOMEM; - init_gssp_clnt(sn); return 0; } diff --git a/net/sunrpc/sunrpc_syms.c b/net/sunrpc/sunrpc_syms.c index ab88ce46afb5..1a3884a0376a 100644 --- a/net/sunrpc/sunrpc_syms.c +++ b/net/sunrpc/sunrpc_syms.c @@ -57,6 +57,7 @@ static __net_init int sunrpc_init_net(struct net *net) INIT_LIST_HEAD(&sn->all_clients); spin_lock_init(&sn->rpc_client_lock); spin_lock_init(&sn->rpcb_clnt_lock); + mutex_init(&sn->gssp_lock); return 0; err_pipefs: