SUNRPC: Fix crasher in gss_unwrap_resp_integ()

[ Upstream commit 8a0fa3f ]

If a zero length is passed to kmalloc() it returns 0x10, which is
not a valid address. gss_unwrap_resp_integ() subsequently crashes
when it attempts to dereference that pointer.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

net/sunrpc/auth_gss/auth_gss.c

@@ -1989,7 +1989,7 @@ gss_unwrap_resp_integ(struct rpc_task *task, struct rpc_cred *cred,
 		goto unwrap_failed;
 	mic.len = len;
 	mic.data = kmalloc(len, GFP_KERNEL);
-	if (!mic.data)
+	if (ZERO_OR_NULL_PTR(mic.data))
 		goto unwrap_failed;
 	if (read_bytes_from_xdr_buf(rcv_buf, offset, mic.data, mic.len))
 		goto unwrap_failed;