[PATCH] nfsd: Initialize ssc before laundromat_work to prevent NULL dereference

[Li Lingfeng]

In nfs4_state_start_net(), laundromat_work may access nfsd_ssc through
nfs4_laundromat -> nfsd4_ssc_expire_umount. If nfsd_ssc isn't initialized,
this can cause NULL pointer dereference.

Normally the delayed start of laundromat_work allows sufficient time for
nfsd_ssc initialization to complete. However, when the kernel waits too
long for userspace responses (e.g. in nfs4_state_start_net ->
nfsd4_end_grace -> nfsd4_record_grace_done -> nfsd4_cld_grace_done ->
cld_pipe_upcall -> __cld_pipe_upcall -> wait_for_completion path), the
delayed work may start before nfsd_ssc initialization finishes.

Fix this by moving nfsd_ssc initialization before starting laundromat_work.

Fixes: f4e44b393389 ("NFSD: delay unmount source's export after inter-server copy completed.")
Signed-off-by: Li Lingfeng <lilingfeng3@xxxxxxxxxx>
---
 fs/nfsd/nfssvc.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index 9b3d6cff0e1e..8ed143ef8b41 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -396,13 +396,13 @@ static int nfsd_startup_net(struct net *net, const struct cred *cred)
 	if (ret)
 		goto out_filecache;
 
+#ifdef CONFIG_NFSD_V4_2_INTER_SSC
+	nfsd4_ssc_init_umount_work(nn);
+#endif
 	ret = nfs4_state_start_net(net);
 	if (ret)
 		goto out_reply_cache;
 
-#ifdef CONFIG_NFSD_V4_2_INTER_SSC
-	nfsd4_ssc_init_umount_work(nn);
-#endif
 	nn->nfsd_net_up = true;
 	return 0;
 
-- 
2.31.1