[PATCH] nfsd: hold cl_lock in client_has_state()

["Cen Zhang (Microsoft Security FORGE Labs)" <blbllhy@gmail.com>]

client_has_openowners() walks clp->cl_openowners and reads so_stateids
without clp->cl_lock. nfs4_put_stateowner() unhashes that openowner under
cl_lock and then frees it, so a concurrent EXCHANGE_ID with mismatched
creds can use-after-free the nfs4_openowner.

BUG: KASAN: slab-use-after-free in client_has_state+0x10a/0x140
  fs/nfsd/nfs4state.c:3718 client_has_openowners()
  nfsd4_exchange_id
  nfsd4_proc_compound
  nfsd_dispatch
  svc_process

Take clp->cl_lock while client_has_state() walks the openowner list.

Fixes: 4eaea1342507 ("nfsd: improve client_has_state to check for unused openowners")
Reported-by: Xiang Mei (Microsoft) <xmei5@asu.edu>
Cc: AutonomousCodeSecurity@microsoft.com
Cc: stable@vger.kernel.org
Signed-off-by: Cen Zhang (Microsoft Security FORGE Labs) <blbllhy@gmail.com>
---
 fs/nfsd/nfs4state.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 18e17232cf94..8d7a4c2eadbe 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -4216,12 +4216,18 @@ nfsd4_set_ex_flags(struct nfs4_client *new, struct nfsd4_exchange_id *clid)
 static bool client_has_openowners(struct nfs4_client *clp)
 {
 	struct nfs4_openowner *oo;
+	bool found = false;
 
+	spin_lock(&clp->cl_lock);
 	list_for_each_entry(oo, &clp->cl_openowners, oo_perclient) {
-		if (!list_empty(&oo->oo_owner.so_stateids))
-			return true;
+		if (!list_empty(&oo->oo_owner.so_stateids)) {
+			found = true;
+			break;
+		}
 	}
-	return false;
+	spin_unlock(&clp->cl_lock);
+
+	return found;
 }
 
 static bool client_has_state(struct nfs4_client *clp)

base-commit: 1b78070aaef63512688aebfbc82365ef9d6660f1
-- 
2.55.0