[SECURITY PATCH 15/28] tftp: Do not use priority queue

[Daniel Kiper <daniel.kiper@oracle.com>]

From: Alexey Makhalov <amakhalov@vmware.com>

There is not need to reassemble the order of blocks. Per RFC 1350,
server must wait for the ACK, before sending next block. Data packets
can be served immediately without putting them to priority queue.

Logic to handle incoming packet is this:
  - if packet block id equal to expected block id, then
    process the packet,
  - if packet block id is less than expected - this is retransmit
    of old packet, then ACK it and drop the packet,
  - if packet block id is more than expected - that shouldn't
    happen, just drop the packet.

It makes the tftp receive path code simpler, smaller and faster.
As a benefit, this change fixes CID# 73624 and CID# 96690, caused
by following while loop:

  while (cmp_block (grub_be_to_cpu16 (tftph->u.data.block), data->block + 1) == 0)

where tftph pointer is not moving from one iteration to another, causing
to serve same packet again. Luckily, double serving didn't happen due to
data->block++ during the first iteration.

Fixes: CID 73624, CID 96690

Signed-off-by: Alexey Makhalov <amakhalov@vmware.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/net/tftp.c | 162 ++++++++++++++++-----------------------------------
 1 file changed, 50 insertions(+), 112 deletions(-)

diff --git a/grub-core/net/tftp.c b/grub-core/net/tftp.c
index b26d2ed7a..644135caf 100644
--- a/grub-core/net/tftp.c
+++ b/grub-core/net/tftp.c
@@ -25,7 +25,6 @@
 #include <grub/mm.h>
 #include <grub/dl.h>
 #include <grub/file.h>
-#include <grub/priority_queue.h>
 #include <grub/i18n.h>
 
 GRUB_MOD_LICENSE ("GPLv3+");
@@ -106,31 +105,8 @@ typedef struct tftp_data
   int have_oack;
   struct grub_error_saved save_err;
   grub_net_udp_socket_t sock;
-  grub_priority_queue_t pq;
 } *tftp_data_t;
 
-static int
-cmp_block (grub_uint16_t a, grub_uint16_t b)
-{
-  grub_int16_t i = (grub_int16_t) (a - b);
-  if (i > 0)
-    return +1;
-  if (i < 0)
-    return -1;
-  return 0;
-}
-
-static int
-cmp (const void *a__, const void *b__)
-{
-  struct grub_net_buff *a_ = *(struct grub_net_buff **) a__;
-  struct grub_net_buff *b_ = *(struct grub_net_buff **) b__;
-  struct tftphdr *a = (struct tftphdr *) a_->data;
-  struct tftphdr *b = (struct tftphdr *) b_->data;
-  /* We want the first elements to be on top.  */
-  return -cmp_block (grub_be_to_cpu16 (a->u.data.block), grub_be_to_cpu16 (b->u.data.block));
-}
-
 static grub_err_t
 ack (tftp_data_t data, grub_uint64_t block)
 {
@@ -207,73 +183,60 @@ tftp_receive (grub_net_udp_socket_t sock __attribute__ ((unused)),
 	  return GRUB_ERR_NONE;
 	}
 
-      err = grub_priority_queue_push (data->pq, &nb);
-      if (err)
-	return err;
+      /* Ack old/retransmitted block. */
+      if (grub_be_to_cpu16 (tftph->u.data.block) < data->block + 1)
+	ack (data, grub_be_to_cpu16 (tftph->u.data.block));
+      /* Ignore unexpected block. */
+      else if (grub_be_to_cpu16 (tftph->u.data.block) > data->block + 1)
+	grub_dprintf ("tftp", "TFTP unexpected block # %d\n", tftph->u.data.block);
+      else
+	{
+	  unsigned size;
 
-      {
-	struct grub_net_buff **nb_top_p, *nb_top;
-	while (1)
-	  {
-	    nb_top_p = grub_priority_queue_top (data->pq);
-	    if (!nb_top_p)
-	      return GRUB_ERR_NONE;
-	    nb_top = *nb_top_p;
-	    tftph = (struct tftphdr *) nb_top->data;
-	    if (cmp_block (grub_be_to_cpu16 (tftph->u.data.block), data->block + 1) >= 0)
-	      break;
-	    ack (data, grub_be_to_cpu16 (tftph->u.data.block));
-	    grub_netbuff_free (nb_top);
-	    grub_priority_queue_pop (data->pq);
-	  }
-	while (cmp_block (grub_be_to_cpu16 (tftph->u.data.block), data->block + 1) == 0)
-	  {
-	    unsigned size;
-
-	    grub_priority_queue_pop (data->pq);
-
-	    if (file->device->net->packs.count < 50)
+	  if (file->device->net->packs.count < 50)
+	    {
 	      err = ack (data, data->block + 1);
-	    else
-	      {
-		file->device->net->stall = 1;
-		err = 0;
-	      }
-	    if (err)
-	      return err;
+	      if (err)
+		return err;
+	    }
+	  else
+	    file->device->net->stall = 1;
 
-	    err = grub_netbuff_pull (nb_top, sizeof (tftph->opcode) +
-				     sizeof (tftph->u.data.block));
-	    if (err)
-	      return err;
-	    size = nb_top->tail - nb_top->data;
+	  err = grub_netbuff_pull (nb, sizeof (tftph->opcode) +
+				   sizeof (tftph->u.data.block));
+	  if (err)
+	    return err;
+	  size = nb->tail - nb->data;
 
-	    data->block++;
-	    if (size < data->block_size)
-	      {
-		if (data->ack_sent < data->block)
-		  ack (data, data->block);
-		file->device->net->eof = 1;
-		file->device->net->stall = 1;
-		grub_net_udp_close (data->sock);
-		data->sock = NULL;
-	      }
-	    /* Prevent garbage in broken cards. Is it still necessary
-	       given that IP implementation has been fixed?
-	     */
-	    if (size > data->block_size)
-	      {
-		err = grub_netbuff_unput (nb_top, size - data->block_size);
-		if (err)
-		  return err;
-	      }
-	    /* If there is data, puts packet in socket list. */
-	    if ((nb_top->tail - nb_top->data) > 0)
-	      grub_net_put_packet (&file->device->net->packs, nb_top);
-	    else
-	      grub_netbuff_free (nb_top);
-	  }
-      }
+	  data->block++;
+	  if (size < data->block_size)
+	    {
+	      if (data->ack_sent < data->block)
+		ack (data, data->block);
+	      file->device->net->eof = 1;
+	      file->device->net->stall = 1;
+	      grub_net_udp_close (data->sock);
+	      data->sock = NULL;
+	    }
+	  /*
+	   * Prevent garbage in broken cards. Is it still necessary
+	   * given that IP implementation has been fixed?
+	   */
+	  if (size > data->block_size)
+	    {
+	      err = grub_netbuff_unput (nb, size - data->block_size);
+	      if (err)
+		return err;
+	    }
+	  /* If there is data, puts packet in socket list. */
+	  if ((nb->tail - nb->data) > 0)
+	    {
+	      grub_net_put_packet (&file->device->net->packs, nb);
+	      /* Do not free nb. */
+	      return GRUB_ERR_NONE;
+	    }
+	}
+      grub_netbuff_free (nb);
       return GRUB_ERR_NONE;
     case TFTP_ERROR:
       data->have_oack = 1;
@@ -287,19 +250,6 @@ tftp_receive (grub_net_udp_socket_t sock __attribute__ ((unused)),
     }
 }
 
-static void
-destroy_pq (tftp_data_t data)
-{
-  struct grub_net_buff **nb_p;
-  while ((nb_p = grub_priority_queue_top (data->pq)))
-    {
-      grub_netbuff_free (*nb_p);
-      grub_priority_queue_pop (data->pq);
-    }
-
-  grub_priority_queue_destroy (data->pq);
-}
-
 /*
  * Create a normalized copy of the filename. Compress any string of consecutive
  * forward slashes to a single forward slash.
@@ -397,17 +347,9 @@ tftp_open (struct grub_file *file, const char *filename)
   file->not_easily_seekable = 1;
   file->data = data;
 
-  data->pq = grub_priority_queue_new (sizeof (struct grub_net_buff *), cmp);
-  if (!data->pq)
-    {
-      grub_free (data);
-      return grub_errno;
-    }
-
   err = grub_net_resolve_address (file->device->net->server, &addr);
   if (err)
     {
-      destroy_pq (data);
       grub_free (data);
       return err;
     }
@@ -417,7 +359,6 @@ tftp_open (struct grub_file *file, const char *filename)
 				  file);
   if (!data->sock)
     {
-      destroy_pq (data);
       grub_free (data);
       return grub_errno;
     }
@@ -431,7 +372,6 @@ tftp_open (struct grub_file *file, const char *filename)
       if (err)
 	{
 	  grub_net_udp_close (data->sock);
-	  destroy_pq (data);
 	  grub_free (data);
 	  return err;
 	}
@@ -448,7 +388,6 @@ tftp_open (struct grub_file *file, const char *filename)
   if (grub_errno)
     {
       grub_net_udp_close (data->sock);
-      destroy_pq (data);
       grub_free (data);
       return grub_errno;
     }
@@ -491,7 +430,6 @@ tftp_close (struct grub_file *file)
 	grub_print_error ();
       grub_net_udp_close (data->sock);
     }
-  destroy_pq (data);
   grub_free (data);
   return GRUB_ERR_NONE;
 }
-- 
2.11.0