[PATCH 5.10 039/798] nfsd: check client ownership when cancelling a copy-notify stateid

5.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jeff Layton <jlayton@kernel.org>

commit 6bdbfab96e0cf25e5f57dac5c09dc1749751a4bf upstream.

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")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260710-nfsd-testing-v3-5-a0ff7db6aa3e@kernel.org (local)
Signed-off-by: Chuck Lever <cel@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/nfsd/nfs4state.c |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c

@@ -6621,10 +6621,20 @@ __be32 manage_cpntf_state(struct nfsd_ne
 			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 creating client may cancel.
+			 * so_id is guessable, so without this check any client
+			 * could free another's cpntf state.
+			 */
+			state = NULL;
+			goto unlock;
+		} else {
 			_free_cpntf_state_locked(nn, state);
+		}
 	}
 unlock:
 	spin_unlock(&nn->s2s_cp_lock);