[PATCH 5.10/5.15] nfsd: don't ignore the return code of svc_proc_register()

[Vladislav Nikolaev <vlad102nikolaev@gmail.com>]

From: Jeff Layton <jlayton@kernel.org>

commit 930b64ca0c511521f0abdd1d57ce52b2a6e3476b upstream.

Currently, nfsd_proc_stat_init() ignores the return value of
svc_proc_register(). If the procfile creation fails, then the kernel
will WARN when it tries to remove the entry later.

Fix nfsd_proc_stat_init() to return the same type of pointer as
svc_proc_register(), and fix up nfsd_net_init() to check that and fail
the nfsd_net construction if it occurs.

svc_proc_register() can fail if the dentry can't be allocated, or if an
identical dentry already exists. The second case is pretty unlikely in
the nfsd_net construction codepath, so if this happens, return -ENOMEM.

Reported-by: syzbot+e34ad04f27991521104c@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-nfs/67a47501.050a0220.19061f.05f9.GAE@google.com/
Cc: stable@vger.kernel.org # v6.9
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Vladislav Nikolaev <vlad102nikolaev@gmail.com>
---
Backport fix for CVE-2025-22026
 fs/nfsd/nfsctl.c | 9 ++++++++-
 fs/nfsd/stats.c  | 4 ++--
 fs/nfsd/stats.h  | 2 +-
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index ba2eaf3744ef..cc0dea883fbd 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1460,17 +1460,24 @@ static __net_init int nfsd_init_net(struct net *net)
 	retval = nfsd_stat_counters_init(nn);
 	if (retval)
 		goto out_repcache_error;
+
 	memset(&nn->nfsd_svcstats, 0, sizeof(nn->nfsd_svcstats));
 	nn->nfsd_svcstats.program = &nfsd_program;
+	if (!nfsd_proc_stat_init(net)) {
+		retval = -ENOMEM;
+		goto out_proc_error;
+	}
+
 	nn->nfsd_versions = NULL;
 	nn->nfsd4_minorversions = NULL;
 	nfsd4_init_leases_net(nn);
 	get_random_bytes(&nn->siphash_key, sizeof(nn->siphash_key));
 	seqlock_init(&nn->writeverf_lock);
-	nfsd_proc_stat_init(net);
 
 	return 0;
 
+out_proc_error:
+	nfsd_stat_counters_destroy(nn);
 out_repcache_error:
 	nfsd_idmap_shutdown(net);
 out_idmap_error:
diff --git a/fs/nfsd/stats.c b/fs/nfsd/stats.c
index 7a58dba0045c..6d1c6067c80e 100644
--- a/fs/nfsd/stats.c
+++ b/fs/nfsd/stats.c
@@ -113,11 +113,11 @@ void nfsd_stat_counters_destroy(struct nfsd_net *nn)
 	nfsd_percpu_counters_destroy(nn->counter, NFSD_STATS_COUNTERS_NUM);
 }
 
-void nfsd_proc_stat_init(struct net *net)
+struct proc_dir_entry *nfsd_proc_stat_init(struct net *net)
 {
 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
 
-	svc_proc_register(net, &nn->nfsd_svcstats, &nfsd_proc_ops);
+	return svc_proc_register(net, &nn->nfsd_svcstats, &nfsd_proc_ops);
 }
 
 void nfsd_proc_stat_shutdown(struct net *net)
diff --git a/fs/nfsd/stats.h b/fs/nfsd/stats.h
index 14525e854cba..b9329285bc1d 100644
--- a/fs/nfsd/stats.h
+++ b/fs/nfsd/stats.h
@@ -15,7 +15,7 @@ void nfsd_percpu_counters_reset(struct percpu_counter *counters, int num);
 void nfsd_percpu_counters_destroy(struct percpu_counter *counters, int num);
 int nfsd_stat_counters_init(struct nfsd_net *nn);
 void nfsd_stat_counters_destroy(struct nfsd_net *nn);
-void nfsd_proc_stat_init(struct net *net);
+struct proc_dir_entry *nfsd_proc_stat_init(struct net *net);
 void nfsd_proc_stat_shutdown(struct net *net);
 
 static inline void nfsd_stats_rc_hits_inc(struct nfsd_net *nn)
-- 
2.47.3