nfsd: release OPEN-decoded posix ACLs via op_release

nfsd4_decode_createhow4() calls nfsd4_decode_fattr4(), which allocates
refcounted struct posix_acl objects via posix_acl_alloc() and stores
them in open->op_pacl and open->op_dpacl. These pointers must be
released once the OPEN compound finishes.

When nfsd4_decode_open_claim4() returns a non-seqid-mutating error,
the dispatcher short-circuits before op_func runs:

    nfsd4_proc_compound()
      if (op->status && op->opnum == OP_OPEN)
          op->status = nfsd4_open_omfg(...)
              if (!seqid_mutating_err(ntohl(op->status)))
                  return op->status;   /* nfsd4_open() never runs */
      ...
      opdesc->op_release(&op->u)  /* must still release op_pacl/op_dpacl */

Before this change OP_OPEN had no .op_release in nfsd4_ops[], and the
release pair lived inside nfsd4_open() at its out_err: label. On the
short-circuit path nfsd4_open() is never invoked, so both posix_acl
refs leak on every malformed OPEN compound that carries valid POSIX
ACL createhow4 attributes.

Add nfsd4_open_release() and wire it as .op_release for OP_OPEN.
posix_acl_release() is NULL-safe, so the single release site covers
both the normal path and the nfsd4_open_omfg short-circuit. Remove
the matching posix_acl_release() pair from nfsd4_open()'s out_err:
label to avoid double-releasing.

The compound loop has two encoding branches: nfsd4_encode_operation()
for normal ops, and nfsd4_encode_replay() for v4.0 replayed ops.
op_release was only called from nfsd4_encode_operation(), so resources
attached to op->u leak on the replay path.

Move the op_release() call out of nfsd4_encode_operation() and the
replay branch, placing it after the if-else in nfsd4_proc_compound().
This gives a single call site in a fairly obviously-correct place,
covering both the normal encoding and replay paths.

Fixes: 5fc51dfc2e ("NFSD: Add support for XDR decoding POSIX draft ACLs")
Cc: stable@vger.kernel.org
Signed-off-by: Chris Mason <clm@meta.com>
Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260601-nfsd-testing-v3-1-a31cd10bdd4f@kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4proc.c

@@ -681,8 +681,6 @@ nfsd4_open(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	nfsd4_cleanup_open_state(cstate, open);
 	nfsd4_bump_seqid(cstate, status);
 out_err:
-	posix_acl_release(open->op_dpacl);
-	posix_acl_release(open->op_pacl);
 	return status;
 }
 
@@ -704,6 +702,13 @@ static __be32 nfsd4_open_omfg(struct svc_rqst *rqstp, struct nfsd4_compound_stat
 	return nfsd4_open(rqstp, cstate, &op->u);
 }
 
+static void
+nfsd4_open_release(union nfsd4_op_u *u)
+{
+	posix_acl_release(u->open.op_dpacl);
+	posix_acl_release(u->open.op_pacl);
+}
+
 /*
  * filehandle-manipulating ops.
  */
@@ -3202,6 +3207,9 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
 			status = op->status;
 		}
 
+		if (op->opdesc && op->opdesc->op_release)
+			op->opdesc->op_release(&op->u);
+
 		trace_nfsd_compound_status(args->client_opcnt, resp->opcnt,
 					   status, nfsd4_op_name(op->opnum));
 
@@ -3701,6 +3709,7 @@ static const struct nfsd4_operation nfsd4_ops[] = {
 	},
 	[OP_OPEN] = {
 		.op_func = nfsd4_open,
+		.op_release = nfsd4_open_release,
 		.op_flags = OP_HANDLES_WRONGSEC | OP_MODIFIES_SOMETHING,
 		.op_name = "OP_OPEN",
 		.op_rsize_bop = nfsd4_open_rsize,

fs/nfsd/nfs4xdr.c

@@ -6403,9 +6403,6 @@ nfsd4_encode_operation(struct nfsd4_compoundres *resp, struct nfsd4_op *op)
 	write_bytes_to_xdr_buf(xdr->buf, op_status_offset,
 			       &op->status, XDR_UNIT);
 release:
-	if (opdesc && opdesc->op_release)
-		opdesc->op_release(&op->u);
-
 	/*
 	 * Account for pages consumed while encoding this operation.
 	 * The xdr_stream primitives don't manage rq_next_page.