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TFTP tweak.

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Check sender of all received packets, as specified in RFC 1350 para 4.

My understanding of the example in the RFC is that it in fact only
applies to server-to-client packets, and packet loss or duplication
cannot result in a client sending from more than one port to a server.
This check is not, therefore, strictly needed on the server side.
It's still useful, and adds a little security against packet
spoofing. (though if you're running TFTP on a public network with
bad actors, nothing can really save you.)
This commit is contained in:
Simon Kelley
2021-03-30 21:21:09 +01:00
parent b5d1b20727
commit dfb1f7ccf1
2 changed files with 24 additions and 3 deletions
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3
CHANGELOG
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@@ -65,6 +65,9 @@ version 2.85
Scale the size of the DNS random-port pool based on the
value of the --dns-forward-max configuration.
Tweak TFTP code to check sender of all recieved packets, as
specified in RFC 1350 para 4.
version 2.84
Fix a problem, introduced in 2.83, which could see DNS replies

24
src/tftp.c
View File

@@ -39,6 +39,7 @@ static void sanitise(char *buf);
#define ERR_PERM 2
#define ERR_FULL 3
#define ERR_ILL 4
#define ERR_TID 5
void tftp_request(struct listener *listen, time_t now)
{
@@ -583,11 +584,27 @@ void check_tftp_listeners(time_t now)
for (transfer = daemon->tftp_trans; transfer; transfer = transfer->next)
if (poll_check(transfer->sockfd, POLLIN))
{
union mysockaddr peer;
socklen_t addr_len = sizeof(union mysockaddr);
ssize_t len;
/* we overwrote the buffer... */
daemon->srv_save = NULL;
handle_tftp(now, transfer, recv(transfer->sockfd, daemon->packet, daemon->packet_buff_sz, 0));
if ((len = recvfrom(transfer->sockfd, daemon->packet, daemon->packet_buff_sz, 0, &peer.sa, &addr_len)) > 0)
{
if (sockaddr_isequal(&peer, &transfer->peer))
handle_tftp(now, transfer, len);
else
{
/* Wrong source address. See rfc1350 para 4. */
prettyprint_addr(&peer, daemon->addrbuff);
len = tftp_err(ERR_TID, daemon->packet, _("ignoring packet from %s (TID mismatch)"), daemon->addrbuff);
sendto(transfer->sockfd, daemon->packet, len, 0, &peer.sa, sa_len(&peer));
}
}
}
for (transfer = daemon->tftp_trans, up = &daemon->tftp_trans; transfer; transfer = tmp)
{
tmp = transfer->next;
@@ -736,7 +753,8 @@ static ssize_t tftp_err(int err, char *packet, char *message, char *file)
char *errstr = strerror(errno);
memset(packet, 0, daemon->packet_buff_sz);
sanitise(file);
if (file)
sanitise(file);
mess->op = htons(OP_ERR);
mess->err = htons(err);