nat: fix potential out-of-bound worker array index

In several NAT submodules, the number of available ports (0xffff - 1024)
may not be divisible by the number of workers, so port_per_thread is
determined by integer division, which is the floor of the quotient.
Later when a worker index is needed, dividing the port with port_per_thread
may yield an out-of-bound array index into the workers array.

As an example, assume 2 workers are configured, then port_per_thread
will be (0xffff - 1024) / 2, which is 32255. When we compute a worker
index with port 0xffff, we get (0xffff - 1024) / 32255, which is 2,
but since we only have 2 workers, only 0 and 1 are valid indices.

This patch fixes the problem by adding a modulo at the end of the division.

Type: fix
Signed-off-by: Jing Peng <pj.hades@gmail.com>
Change-Id: Ieae3d5faf716410422610484a68222f1c957f3f8

1 files changed, 16 insertions, 16 deletions

diff --git a/src/plugins/nat/nat44-ei/nat44_ei.c b/src/plugins/nat/nat44-ei/nat44_ei.c
index 30c61b21d91..4f2fa6112d5 100644
--- a/src/plugins/nat/nat44-ei/nat44_ei.c
+++ b/src/plugins/nat/nat44-ei/nat44_ei.c
@@ -1684,6 +1684,20 @@ nat44_ei_get_in2out_worker_index (ip4_header_t *ip0, u32 rx_fib_index0,
 }
 
 u32
+nat44_ei_get_thread_idx_by_port (u16 e_port)
+{
+  nat44_ei_main_t *nm = &nat44_ei_main;
+  u32 thread_idx = nm->num_workers;
+  if (nm->num_workers > 1)
+    {
+      thread_idx = nm->first_worker_index +
+		   nm->workers[(e_port - 1024) / nm->port_per_thread %
+			       _vec_len (nm->workers)];
+    }
+  return thread_idx;
+}
+
+u32
 nat44_ei_get_out2in_worker_index (vlib_buffer_t *b, ip4_header_t *ip0,
 				  u32 rx_fib_index0, u8 is_output)
 {
@@ -1761,9 +1775,8 @@ nat44_ei_get_out2in_worker_index (vlib_buffer_t *b, ip4_header_t *ip0,
     }
 
   /* worker by outside port */
-  next_worker_index = nm->first_worker_index;
-  next_worker_index +=
-    nm->workers[(clib_net_to_host_u16 (port) - 1024) / nm->port_per_thread];
+  next_worker_index =
+    nat44_ei_get_thread_idx_by_port (clib_net_to_host_u16 (port));
   return next_worker_index;
 }
 
@@ -2050,19 +2063,6 @@ nat44_ei_del_session (nat44_ei_main_t *nm, ip4_address_t *addr, u16 port,
   return VNET_API_ERROR_NO_SUCH_ENTRY;
 }
 
-u32
-nat44_ei_get_thread_idx_by_port (u16 e_port)
-{
-  nat44_ei_main_t *nm = &nat44_ei_main;
-  u32 thread_idx = nm->num_workers;
-  if (nm->num_workers > 1)
-    {
-      thread_idx = nm->first_worker_index +
-		   nm->workers[(e_port - 1024) / nm->port_per_thread];
-    }
-  return thread_idx;
-}
-
 void
 nat44_ei_add_del_addr_to_fib (ip4_address_t *addr, u8 p_len, u32 sw_if_index,
 			      int is_add)