In the old TFTP server, there was an undocumented behavior where

the block counter would rollover to 0 if a file larger
than 65535 blocks was transferred.  With the default block size
of 512 octets per block, this is a file size of approximately 32 megabytes.

The new TFTP server code would report an error and stop transferring
the file if a file was larger than 65535 blocks.

This patch restores the old TFTP server's behavior to the new
TFTP server code.  If a TFTP client transfers a file larger
than 65535 blocks, and does *not* specify the "rollover" option,
then automatically rollover the block counter to 0 every time
we reach 65535 blocks.

This restores interoperability with the FreeBSD 6 TFTP client.
Without this change, if a FreeBSD 6 TFTP client tried to
retrieve a file larger than 65535 blocks from a FreeBSD 9 TFTP server
, the transfer would fail.
The same file could be retrieved successfully if the same FreeBSD 6
TFTP client was used against a FreeBSD 6 TFTP server.

Approved by:  re (kib)
Tested by: Pawan Gupta <pawang at juniper dot net>,
Obtained from:  Juniper Networks

1 files changed, 16 insertions, 12 deletions

diff --git a/libexec/tftpd/tftp-transfer.c b/libexec/tftpd/tftp-transfer.c
index fd0e00d..d0c8a95 100644
--- a/libexec/tftpd/tftp-transfer.c
+++ b/libexec/tftpd/tftp-transfer.c
@@ -129,14 +129,16 @@ tftp_send(int peer, uint16_t *block, struct tftp_stats *ts)
 		(*block)++;
 		if (oldblock > *block) {
 			if (options[OPT_ROLLOVER].o_request == NULL) {
-				tftp_log(LOG_ERR,
-				    "Block rollover but not allowed.");
-				send_error(peer, EBADOP);
-				gettimeofday(&(ts->tstop), NULL);
-				return;
+				/*
+				 * "rollover" option not specified in
+				 * tftp client.  Default to rolling block
+				 * counter to 0.
+				 */
+				*block = 0;
+			} else {
+				*block = atoi(options[OPT_ROLLOVER].o_request);
 			}
 
-			*block = atoi(options[OPT_ROLLOVER].o_request);
 			ts->rollovers++;
 		}
 		gettimeofday(&(ts->tstop), NULL);
@@ -196,14 +198,16 @@ tftp_receive(int peer, uint16_t *block, struct tftp_stats *ts,
 		(*block)++;
 		if (oldblock > *block) {
 			if (options[OPT_ROLLOVER].o_request == NULL) {
-				tftp_log(LOG_ERR,
-				    "Block rollover but not allowed.");
-				send_error(peer, EBADOP);
-				gettimeofday(&(ts->tstop), NULL);
-				return;
+				/*
+				 * "rollover" option not specified in
+				 * tftp client.  Default to rolling block
+				 * counter to 0.
+				 */
+				*block = 0;
+			} else {
+				*block = atoi(options[OPT_ROLLOVER].o_request);
 			}
 
-			*block = atoi(options[OPT_ROLLOVER].o_request);
 			ts->rollovers++;
 		}