[Dnsmasq-discuss] [PATCH] Add support for unique TFTP root per MAC

Floris Bos

2017-04-01 19:25:31 UTC

It is currently only possible to let the TFTP server serve a different
folder depending on the client's IP address.
However it isn't always possible to predict what the client's
IP address will be, especially in situations in which we are not
responsible for handing them out (e.g. proxy dhcp setups).

Extend the current --tftp-unique-root parameter to support having a
separate folder per MAC address instead.

Signed-off-by: Floris Bos <***@je-eigen-domein.nl>
---
man/dnsmasq.8 | 16 ++++++++++------
src/dnsmasq.h | 5 +++--
src/option.c | 13 +++++++++++--
src/tftp.c | 34 +++++++++++++++++++++++++++++++++-
4 files changed, 57 insertions(+), 11 deletions(-)

diff --git a/man/dnsmasq.8 b/man/dnsmasq.8
index 05f800c..787c104 100644
--- a/man/dnsmasq.8
+++ b/man/dnsmasq.8
@@ -1814,12 +1814,16 @@ directory is only used for TFTP requests via that interface.
.B --tftp-no-fail
Do not abort startup if specified tftp root directories are inaccessible.
.TP
-.B --tftp-unique-root
-Add the IP address of the TFTP client as a path component on the end
-of the TFTP-root (in standard dotted-quad format). Only valid if a
-tftp-root is set and the directory exists. For instance, if tftp-root is "/tftp" and client
-1.2.3.4 requests file "myfile" then the effective path will be
-"/tftp/1.2.3.4/myfile" if /tftp/1.2.3.4 exists or /tftp/myfile otherwise.
+.B --tftp-unique-root[=ip|mac]
+Add the IP or hardware address of the TFTP client as a path component on the end
+of the TFTP-root. Only valid if a tftp-root is set and the directory exists.
+Defaults to adding IP address (in standard dotted-quad format).
+For instance, if tftp-root is "/tftp" and client 1.2.3.4 requests file "myfile"
+then the effective path will be "/tftp/1.2.3.4/myfile" if /tftp/1.2.3.4 exists or /tftp/myfile otherwise.
+When "=mac" is specified it will append the MAC address instead, using lowercase zero padded digits
+separated by dashes, e.g.: 01-02-03-04-aa-bb
+Note that resolving MAC addresses is only possible if the client is in the local network or obtained
+a DHCP lease from us.
.TP
.B --tftp-secure
Enable TFTP secure mode: without this, any file which is readable by
diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index 40f249f..25e4ad9 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -211,7 +211,7 @@ struct event_desc {
#define OPT_TFTP_SECURE 26
#define OPT_TFTP_NOBLOCK 27
#define OPT_LOG_OPTS 28
-#define OPT_TFTP_APREF 29
+#define OPT_TFTP_APREF_IP 29
#define OPT_NO_OVERRIDE 30
#define OPT_NO_REBIND 31
#define OPT_ADD_MAC 32
@@ -238,7 +238,8 @@ struct event_desc {
#define OPT_SCRIPT_ARP 53
#define OPT_MAC_B64 54
#define OPT_MAC_HEX 55
-#define OPT_LAST 56
+#define OPT_TFTP_APREF_MAC 56
+#define OPT_LAST 57

/* extra flags for my_syslog, we use a couple of facilities since they are known
not to occupy the same bits as priorities, no matter how syslog.h is set up. */
diff --git a/src/option.c b/src/option.c
index 12350cb..00e1d44 100644
--- a/src/option.c
+++ b/src/option.c
@@ -243,7 +243,7 @@ static const struct myoption opts[] =
{ "enable-tftp", 2, 0, LOPT_TFTP },
{ "tftp-secure", 0, 0, LOPT_SECURE },
{ "tftp-no-fail", 0, 0, LOPT_TFTP_NO_FAIL },
- { "tftp-unique-root", 0, 0, LOPT_APREF },
+ { "tftp-unique-root", 2, 0, LOPT_APREF },
{ "tftp-root", 1, 0, LOPT_PREFIX },
{ "tftp-max", 1, 0, LOPT_TFTP_MAX },
{ "tftp-mtu", 1, 0, LOPT_TFTP_MTU },
@@ -432,7 +432,7 @@ static struct {
{ LOPT_OVERRIDE, OPT_NO_OVERRIDE, NULL, gettext_noop("Do NOT reuse filename and server fields for extra DHCP options."), NULL },
{ LOPT_TFTP, ARG_DUP, "[=<intr>[,<intr>]]", gettext_noop("Enable integrated read-only TFTP server."), NULL },
{ LOPT_PREFIX, ARG_DUP, "<dir>[,<iface>]", gettext_noop("Export files by TFTP only from the specified subtree."), NULL },
- { LOPT_APREF, OPT_TFTP_APREF, NULL, gettext_noop("Add client IP address to tftp-root."), NULL },
+ { LOPT_APREF, ARG_DUP, "[=ip|mac]", gettext_noop("Add client IP or hardware address to tftp-root."), NULL },
{ LOPT_SECURE, OPT_TFTP_SECURE, NULL, gettext_noop("Allow access only to files owned by the user running dnsmasq."), NULL },
{ LOPT_TFTP_NO_FAIL, OPT_TFTP_NO_FAIL, NULL, gettext_noop("Do not terminate the service if TFTP directories are inaccessible."), NULL },
{ LOPT_TFTP_MAX, ARG_ONE, "<integer>", gettext_noop("Maximum number of concurrent TFTP transfers (defaults to %s)."), "#" },
@@ -2720,6 +2720,15 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
}

break;
+
+ case LOPT_APREF: /* --tftp-unique-root */
+ if (!arg || strcasecmp(arg, "ip") == 0)
+ set_option_bool(OPT_TFTP_APREF_IP);
+ else if (strcasecmp(arg, "mac") == 0)
+ set_option_bool(OPT_TFTP_APREF_MAC);
+ else
+ ret_err(gen_err);
+ break;
#endif

case LOPT_BRIDGE: /* --bridge-interface */
diff --git a/src/tftp.c b/src/tftp.c
index f8ce9d2..d425a10 100644
--- a/src/tftp.c
+++ b/src/tftp.c
@@ -382,7 +382,7 @@ void tftp_request(struct listener *listen, time_t now)
if (prefix[strlen(prefix)-1] != '/')
strncat(daemon->namebuff, "/", (MAXDNAME-1) - strlen(daemon->namebuff));

- if (option_bool(OPT_TFTP_APREF))
+ if (option_bool(OPT_TFTP_APREF_IP))
{
size_t oldlen = strlen(daemon->namebuff);
struct stat statbuf;
@@ -394,6 +394,38 @@ void tftp_request(struct listener *listen, time_t now)
if (stat(daemon->namebuff, &statbuf) == -1 || !S_ISDIR(statbuf.st_mode))
daemon->namebuff[oldlen] = 0;
}
+ if (option_bool(OPT_TFTP_APREF_MAC))
+ {
+ unsigned char *macaddr = NULL;
+ unsigned char macbuf[DHCP_CHADDR_MAX];
+
+#ifdef HAVE_DHCP
+ if (daemon->dhcp && peer.sa.sa_family == AF_INET)
+ {
+ /* Check if the client IP is in our lease database */
+ struct dhcp_lease *lease = lease_find_by_addr(peer.in.sin_addr);
+ if (lease && lease->hwaddr_type == ARPHRD_ETHER && lease->hwaddr_len == ETHER_ADDR_LEN)
+ macaddr = lease->hwaddr;
+ }
+#endif
+
+ /* If no luck, try to find in ARP table. This only works if client is in same (V)LAN */
+ if (!macaddr && find_mac(&peer, macbuf, 1, now) > 0)
+ macaddr = macbuf;
+
+ if (macaddr)
+ {
+ size_t oldlen = strlen(daemon->namebuff);
+ struct stat statbuf;
+
+ snprintf(daemon->namebuff+oldlen, sizeof(daemon->namebuff)-oldlen, "%.2x-%.2x-%.2x-%.2x-%.2x-%.2x/",
+ macaddr[0], macaddr[1], macaddr[2], macaddr[3], macaddr[4], macaddr[5]);
+
+ /* remove unique-directory if it doesn't exist */
+ if (stat(daemon->namebuff, &statbuf) == -1 || !S_ISDIR(statbuf.st_mode))
+ daemon->namebuff[oldlen] = 0;
+ }
+ }

/* Absolute pathnames OK if they match prefix */
if (filename[0] == '/')

--
2.7.4