Gracefully handle ACKs from the future

diff --git a/tftp.c b/tftp.c
index f0f0457b8525e4cfaff4f95cd37bc9b8b44879cb..ffeff2b19d536910425b2163524f4d16356a04a2 100644 (file)
--- a/tftp.c
+++ b/tftp.c
@@ -222,9 +222,9 @@ inline void sock_perror(const char *msg)
 int tftp_put(struct nmrpd_args *args)
 {
        struct sockaddr_in addr;
-       uint16_t block, port;
+       uint16_t block, ackblock, port;
        ssize_t len, last_len;
-       int fd, sock, ret, timeout;
+       int fd, sock, ret, timeout, errors;
        char rx[TFTP_PKT_SIZE], tx[TFTP_PKT_SIZE];
 
        sock = -1;
@@ -255,13 +255,16 @@ int tftp_put(struct nmrpd_args *args)
        block = 0;
        last_len = -1;
        len = 0;
+       errors = 0;
        /* Not really, but this way the loop sends our WRQ before receiving */
        timeout = 1;
 
        pkt_mkwrq(tx, args->filename);
 
        do {
-               if (timeout || (pkt_num(rx) == ACK && pkt_num(rx + 2) == block)) {
+               ackblock = pkt_num(rx) == ACK ? pkt_num(rx + 2) : -1;
+
+               if (timeout || ackblock == block) {
                        if (!timeout) {
                                ++block;
                                pkt_mknum(tx, DATA);
@@ -284,10 +287,18 @@ int tftp_put(struct nmrpd_args *args)
                        if (ret < 0) {
                                goto cleanup;
                        }
-               } else if (pkt_num(rx) != ACK) {
-                       fprintf(stderr, "Expected ACK(%d), got ", block);
-                       pkt_print(rx, stderr);
-                       fprintf(stderr, "!\n");
+               } else if (pkt_num(rx) != ACK || ackblock > block) {
+                       if (verbosity) {
+                               fprintf(stderr, "Expected ACK(%d), got ", block);
+                               pkt_print(rx, stderr);
+                               fprintf(stderr, ".\n");
+                       }
+
+                       if (ackblock != -1 && ++errors > 5) {
+                               fprintf(stderr, "Protocol error; bailing out.\n");
+                               ret = -1;
+                               goto cleanup;
+                       }
                }
 
                ret = tftp_recvfrom(sock, rx, &port, args->rx_timeout);