[PATCH v2 05/10] nfsd: check client ownership when cancelling a copy-notify stateid

[Jeff Layton <jlayton@kernel.org>]

On the OFFLOAD_CANCEL path (clp != NULL), manage_cpntf_state() freed the
target cpntf state without checking ownership. The lookup key
st->si_opaque.so_id is allocated cyclically (guessable) and the embedded
clientid is the fixed per-net nn->s2s_cp_cl_id, so any authenticated
NFSv4.2 client could cancel and free another client's copy-notify
stateid.

Compare the creating clientid recorded in state->cp_p_clid against the
requesting client's cl_clientid and return nfserr_bad_stateid on a
mismatch instead of freeing the entry.

Fixes: ce0887ac96d3 ("NFSD add nfs4 inter ssc to nfsd4_copy")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/nfs4state.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 1ef015cbc055..76c0e08711df 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -7916,10 +7916,22 @@ __be32 manage_cpntf_state(struct nfsd_net *nn, stateid_t *st,
 			state = NULL;
 			goto unlock;
 		}
-		if (!clp)
+		if (!clp) {
 			refcount_inc(&state->cp_stateid.cs_count);
-		else
+		} else if (memcmp(&clp->cl_clientid, &state->cp_p_clid,
+				  sizeof(clientid_t))) {
+			/*
+			 * OFFLOAD_CANCEL: only the client that created the
+			 * copy-notify stateid may cancel it. so_id values are
+			 * cyclic and guessable, so without this check any
+			 * authenticated client could free another client's
+			 * cpntf state.
+			 */
+			state = NULL;
+			goto unlock;
+		} else {
 			_free_cpntf_state_locked(nn, state);
+		}
 	}
 unlock:
 	spin_unlock(&nn->s2s_cp_lock);

-- 
2.55.0