tftpd: Fix data corruption bug with netascii

Transferring files in netascii format requires, among other things,
translating all CR characters to a CR,NUL pair. tftpd does this correctly
except when the CR occurs as the last octet of a packet. In that case, it
erroneously drops the NUL which should be part of the following packet. The
bug was caused by using 0 as a sentinel value in a variable that could
legitimately hold 0. Fix it by switching the sentinel value to -1.

PR:		178055
Reported by:	Richard <rsitze@gmail.com>
Reviewed by:	cem
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D16853

1 files changed, 5 insertions, 5 deletions

diff --git a/libexec/tftpd/tftp-file.c b/libexec/tftpd/tftp-file.c
index 3e06f5df6edb..a8e7bcf9228b 100644
--- a/libexec/tftpd/tftp-file.c
+++ b/libexec/tftpd/tftp-file.c
@@ -110,10 +110,10 @@ convert_to_net(char *buffer, size_t count, int init)
 {
 	size_t i;
 	static size_t n = 0, in = 0;
-	static int newline = 0;
+	static int newline = -1;
 
 	if (init) {
-		newline = 0;
+		newline = -1;
 		n = 0;
 		in = 0;
 		return 0 ;
@@ -124,9 +124,9 @@ convert_to_net(char *buffer, size_t count, int init)
 	 */
 	i = 0;
 
-	if (newline) {
+	if (newline != -1) {
 		buffer[i++] = newline;
-		newline = 0;
+		newline = -1;
 	}
 
 	while (i < count) {
@@ -161,7 +161,7 @@ convert_to_net(char *buffer, size_t count, int init)
 
 	if (i > count) {
 		/*
-		 * Whoops... that isn't alllowed (but it will happen
+		 * Whoops... that isn't allowed (but it will happen
 		 * when there is a CR or LF at the end of the buffer)
 		 */
 		newline = buffer[i-1];