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putty-source/sshverstring.c
Simon Tatham ad0c502cef Refactor the LogContext type. 
LogContext is now the owner of the logevent() function that back ends
and so forth are constantly calling. Previously, logevent was owned by
the Frontend, which would store the message into its list for the GUI
Event Log dialog (or print it to standard error, or whatever) and then
pass it _back_ to LogContext to write to the currently open log file.
Now it's the other way round: LogContext gets the message from the
back end first, writes it to its log file if it feels so inclined, and
communicates it back to the front end.

This means that lots of parts of the back end system no longer need to
have a pointer to a full-on Frontend; the only thing they needed it
for was logging, so now they just have a LogContext (which many of
them had to have anyway, e.g. for logging SSH packets or session
traffic).

LogContext itself also doesn't get a full Frontend pointer any more:
it now talks back to the front end via a little vtable of its own
called LogPolicy, which contains the method that passes Event Log
entries through, the old askappend() function that decides whether to
truncate a pre-existing log file, and an emergency function for
printing an especially prominent message if the log file can't be
created. One minor nice effect of this is that console and GUI apps
can implement that last function subtly differently, so that Unix
console apps can write it with a plain \n instead of the \r\n
(harmless but inelegant) that the old centralised implementation
generated.

One other consequence of this is that the LogContext has to be
provided to backend_init() so that it's available to backends from the
instant of creation, rather than being provided via a separate API
call a couple of function calls later, because backends have typically
started doing things that need logging (like making network
connections) before the call to backend_provide_logctx. Fortunately,
there's no case in the whole code base where we don't already have
logctx by the time we make a backend (so I don't actually remember why
I ever delayed providing one). So that shortens the backend API by one
function, which is always nice.

While I'm tidying up, I've also moved the printf-style logeventf() and
the handy logevent_and_free() into logging.c, instead of having copies
of them scattered around other places. This has also let me remove
some stub functions from a couple of outlying applications like
Pageant. Finally, I've removed the pointless "_tag" at the end of
LogContext's official struct name.
2018-10-10 21:50:50 +01:00

630 lines
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/*
* Code to handle the initial SSH version string exchange.
*/
#include <assert.h>
#include <string.h>
#include <stdlib.h>
#include "putty.h"
#include "ssh.h"
#include "sshbpp.h"
#include "sshcr.h"
#define PREFIX_MAXLEN 64
struct ssh_verstring_state {
int crState;
Conf *conf;
ptrlen prefix_wanted;
char *our_protoversion;
struct ssh_version_receiver *receiver;
int send_early;
int found_prefix;
int major_protoversion;
int remote_bugs;
char prefix[PREFIX_MAXLEN];
char *vstring;
int vslen, vstrsize;
char *protoversion;
const char *softwareversion;
char *our_vstring;
int i;
BinaryPacketProtocol bpp;
};
static void ssh_verstring_free(BinaryPacketProtocol *bpp);
static void ssh_verstring_handle_input(BinaryPacketProtocol *bpp);
static void ssh_verstring_handle_output(BinaryPacketProtocol *bpp);
static PktOut *ssh_verstring_new_pktout(int type);
static void ssh_verstring_queue_disconnect(BinaryPacketProtocol *bpp,
const char *msg, int category);
static const struct BinaryPacketProtocolVtable ssh_verstring_vtable = {
ssh_verstring_free,
ssh_verstring_handle_input,
ssh_verstring_handle_output,
ssh_verstring_new_pktout,
ssh_verstring_queue_disconnect,
};
static void ssh_detect_bugs(struct ssh_verstring_state *s);
static int ssh_version_includes_v1(const char *ver);
static int ssh_version_includes_v2(const char *ver);
BinaryPacketProtocol *ssh_verstring_new(
Conf *conf, LogContext *logctx, int bare_connection_mode,
const char *protoversion, struct ssh_version_receiver *rcv)
{
struct ssh_verstring_state *s = snew(struct ssh_verstring_state);
memset(s, 0, sizeof(struct ssh_verstring_state));
if (!bare_connection_mode) {
s->prefix_wanted = PTRLEN_LITERAL("SSH-");
} else {
/*
* Ordinary SSH begins with the banner "SSH-x.y-...". Here,
* we're going to be speaking just the ssh-connection
* subprotocol, extracted and given a trivial binary packet
* protocol, so we need a new banner.
*
* The new banner is like the ordinary SSH banner, but
* replaces the prefix 'SSH-' at the start with a new name. In
* proper SSH style (though of course this part of the proper
* SSH protocol _isn't_ subject to this kind of
* DNS-domain-based extension), we define the new name in our
* extension space.
*/
s->prefix_wanted = PTRLEN_LITERAL(
"SSHCONNECTION@putty.projects.tartarus.org-");
}
assert(s->prefix_wanted.len <= PREFIX_MAXLEN);
s->conf = conf_copy(conf);
s->bpp.logctx = logctx;
s->our_protoversion = dupstr(protoversion);
s->receiver = rcv;
/*
* We send our version string early if we can. But if it includes
* SSH-1, we can't, because we have to take the other end into
* account too (see below).
*/
s->send_early = !ssh_version_includes_v1(protoversion);
s->bpp.vt = &ssh_verstring_vtable;
ssh_bpp_common_setup(&s->bpp);
return &s->bpp;
}
void ssh_verstring_free(BinaryPacketProtocol *bpp)
{
struct ssh_verstring_state *s =
container_of(bpp, struct ssh_verstring_state, bpp);
conf_free(s->conf);
sfree(s->vstring);
sfree(s->protoversion);
sfree(s->our_vstring);
sfree(s->our_protoversion);
sfree(s);
}
static int ssh_versioncmp(const char *a, const char *b)
{
char *ae, *be;
unsigned long av, bv;
av = strtoul(a, &ae, 10);
bv = strtoul(b, &be, 10);
if (av != bv)
return (av < bv ? -1 : +1);
if (*ae == '.')
ae++;
if (*be == '.')
be++;
av = strtoul(ae, &ae, 10);
bv = strtoul(be, &be, 10);
if (av != bv)
return (av < bv ? -1 : +1);
return 0;
}
static int ssh_version_includes_v1(const char *ver)
{
return ssh_versioncmp(ver, "2.0") < 0;
}
static int ssh_version_includes_v2(const char *ver)
{
return ssh_versioncmp(ver, "1.99") >= 0;
}
static void ssh_verstring_send(struct ssh_verstring_state *s)
{
BinaryPacketProtocol *bpp = &s->bpp; /* for bpp_logevent */
char *p;
int sv_pos;
/*
* Construct our outgoing version string.
*/
s->our_vstring = dupprintf(
"%.*s%s-%s",
(int)s->prefix_wanted.len, (const char *)s->prefix_wanted.ptr,
s->our_protoversion, sshver);
sv_pos = s->prefix_wanted.len + strlen(s->our_protoversion) + 1;
/* Convert minus signs and spaces in the software version string
* into underscores. */
for (p = s->our_vstring + sv_pos; *p; p++) {
if (*p == '-' || *p == ' ')
*p = '_';
}
#ifdef FUZZING
/*
* Replace the first character of the string with an "I" if we're
* compiling this code for fuzzing - i.e. the protocol prefix
* becomes "ISH-" instead of "SSH-".
*
* This is irrelevant to any real client software (the only thing
* reading the output of PuTTY built for fuzzing is the fuzzer,
* which can adapt to whatever it sees anyway). But it's a safety
* precaution making it difficult to accidentally run such a
* version of PuTTY (which would be hugely insecure) against a
* live peer implementation.
*
* (So the replacement prefix "ISH" notionally stands for
* 'Insecure Shell', of course.)
*/
s->our_vstring[0] = 'I';
#endif
/*
* Now send that version string, plus trailing \r\n or just \n
* (the latter in SSH-1 mode).
*/
bufchain_add(s->bpp.out_raw, s->our_vstring, strlen(s->our_vstring));
if (ssh_version_includes_v2(s->our_protoversion))
bufchain_add(s->bpp.out_raw, "\015", 1);
bufchain_add(s->bpp.out_raw, "\012", 1);
bpp_logevent(("We claim version: %s", s->our_vstring));
}
#define BPP_WAITFOR(minlen) do \
{ \
crMaybeWaitUntilV( \
s->bpp.input_eof || \
bufchain_size(s->bpp.in_raw) >= (minlen)); \
if (s->bpp.input_eof) \
goto eof; \
} while (0)
void ssh_verstring_handle_input(BinaryPacketProtocol *bpp)
{
struct ssh_verstring_state *s =
container_of(bpp, struct ssh_verstring_state, bpp);
crBegin(s->crState);
/*
* If we're sending our version string up front before seeing the
* other side's, then do it now.
*/
if (s->send_early)
ssh_verstring_send(s);
/*
* Search for a line beginning with the protocol name prefix in
* the input.
*/
s->i = 0;
while (1) {
/*
* Every time round this loop, we're at the start of a new
* line, so look for the prefix.
*/
BPP_WAITFOR(s->prefix_wanted.len);
bufchain_fetch(s->bpp.in_raw, s->prefix, s->prefix_wanted.len);
if (!memcmp(s->prefix, s->prefix_wanted.ptr, s->prefix_wanted.len)) {
bufchain_consume(s->bpp.in_raw, s->prefix_wanted.len);
break;
}
/*
* If we didn't find it, consume data until we see a newline.
*/
while (1) {
int len;
void *data;
char *nl;
/* Wait to receive at least 1 byte, but then consume more
* than that if it's there. */
BPP_WAITFOR(1);
bufchain_prefix(s->bpp.in_raw, &data, &len);
if ((nl = memchr(data, '\012', len)) != NULL) {
bufchain_consume(s->bpp.in_raw, nl - (char *)data + 1);
break;
} else {
bufchain_consume(s->bpp.in_raw, len);
}
}
}
s->found_prefix = TRUE;
/*
* Start a buffer to store the full greeting line.
*/
s->vstrsize = s->prefix_wanted.len + 16;
s->vstring = snewn(s->vstrsize, char);
memcpy(s->vstring, s->prefix_wanted.ptr, s->prefix_wanted.len);
s->vslen = s->prefix_wanted.len;
/*
* Now read the rest of the greeting line.
*/
s->i = 0;
do {
int len;
void *data;
char *nl;
crMaybeWaitUntilV(bufchain_size(s->bpp.in_raw) > 0);
bufchain_prefix(s->bpp.in_raw, &data, &len);
if ((nl = memchr(data, '\012', len)) != NULL) {
len = nl - (char *)data + 1;
}
if (s->vslen + len >= s->vstrsize - 1) {
s->vstrsize = (s->vslen + len) * 5 / 4 + 32;
s->vstring = sresize(s->vstring, s->vstrsize, char);
}
memcpy(s->vstring + s->vslen, data, len);
s->vslen += len;
bufchain_consume(s->bpp.in_raw, len);
} while (s->vstring[s->vslen-1] != '\012');
/*
* Trim \r and \n from the version string, and replace them with
* a NUL terminator.
*/
while (s->vslen > 0 &&
(s->vstring[s->vslen-1] == '\r' ||
s->vstring[s->vslen-1] == '\n'))
s->vslen--;
s->vstring[s->vslen] = '\0';
bpp_logevent(("Remote version: %s", s->vstring));
/*
* Pick out the protocol version and software version. The former
* goes in a separately allocated string, so that s->vstring
* remains intact for later use in key exchange; the latter is the
* tail of s->vstring, so it doesn't need to be allocated.
*/
{
const char *pv_start = s->vstring + s->prefix_wanted.len;
int pv_len = strcspn(pv_start, "-");
s->protoversion = dupprintf("%.*s", pv_len, pv_start);
s->softwareversion = pv_start + pv_len;
if (*s->softwareversion) {
assert(*s->softwareversion == '-');
s->softwareversion++;
}
}
ssh_detect_bugs(s);
/*
* Figure out what actual SSH protocol version we're speaking.
*/
if (ssh_version_includes_v2(s->our_protoversion) &&
ssh_version_includes_v2(s->protoversion)) {
/*
* We're doing SSH-2.
*/
s->major_protoversion = 2;
} else if (ssh_version_includes_v1(s->our_protoversion) &&
ssh_version_includes_v1(s->protoversion)) {
/*
* We're doing SSH-1.
*/
s->major_protoversion = 1;
/*
* There are multiple minor versions of SSH-1, and the
* protocol does not specify that the minimum of client
* and server versions is used. So we must adjust our
* outgoing protocol version to be no higher than that of
* the other side.
*/
if (!s->send_early &&
ssh_versioncmp(s->our_protoversion, s->protoversion) > 0) {
sfree(s->our_protoversion);
s->our_protoversion = dupstr(s->protoversion);
}
} else {
/*
* Unable to agree on a major protocol version at all.
*/
if (!ssh_version_includes_v2(s->our_protoversion)) {
ssh_sw_abort(s->bpp.ssh,
"SSH protocol version 1 required by our "
"configuration but not provided by remote");
} else {
ssh_sw_abort(s->bpp.ssh,
"SSH protocol version 2 required by our "
"configuration but remote only provides "
"(old, insecure) SSH-1");
}
crStopV;
}
bpp_logevent(("Using SSH protocol version %d", s->major_protoversion));
if (!s->send_early) {
/*
* If we didn't send our version string early, construct and
* send it now, because now we know what it is.
*/
ssh_verstring_send(s);
}
/*
* And we're done. Notify our receiver that we now know our
* protocol version. This will cause it to disconnect us from the
* input stream and ultimately free us, because our job is now
* done.
*/
s->receiver->got_ssh_version(s->receiver, s->major_protoversion);
return;
eof:
ssh_remote_error(s->bpp.ssh,
"Server unexpectedly closed network connection");
return; /* avoid touching s now it's been freed */
crFinishV;
}
static PktOut *ssh_verstring_new_pktout(int type)
{
assert(0 && "Should never try to send packets during SSH version "
"string exchange");
return NULL;
}
static void ssh_verstring_handle_output(BinaryPacketProtocol *bpp)
{
if (pq_peek(&bpp->out_pq)) {
assert(0 && "Should never try to send packets during SSH version "
"string exchange");
}
}
/*
* Examine the remote side's version string, and compare it against a
* list of known buggy implementations.
*/
static void ssh_detect_bugs(struct ssh_verstring_state *s)
{
BinaryPacketProtocol *bpp = &s->bpp; /* for bpp_logevent */
const char *imp = s->softwareversion;
s->remote_bugs = 0;
/*
* General notes on server version strings:
* - Not all servers reporting "Cisco-1.25" have all the bugs listed
* here -- in particular, we've heard of one that's perfectly happy
* with SSH1_MSG_IGNOREs -- but this string never seems to change,
* so we can't distinguish them.
*/
if (conf_get_int(s->conf, CONF_sshbug_ignore1) == FORCE_ON ||
(conf_get_int(s->conf, CONF_sshbug_ignore1) == AUTO &&
(!strcmp(imp, "1.2.18") || !strcmp(imp, "1.2.19") ||
!strcmp(imp, "1.2.20") || !strcmp(imp, "1.2.21") ||
!strcmp(imp, "1.2.22") || !strcmp(imp, "Cisco-1.25") ||
!strcmp(imp, "OSU_1.4alpha3") || !strcmp(imp, "OSU_1.5alpha4")))) {
/*
* These versions don't support SSH1_MSG_IGNORE, so we have
* to use a different defence against password length
* sniffing.
*/
s->remote_bugs |= BUG_CHOKES_ON_SSH1_IGNORE;
bpp_logevent(("We believe remote version has SSH-1 ignore bug"));
}
if (conf_get_int(s->conf, CONF_sshbug_plainpw1) == FORCE_ON ||
(conf_get_int(s->conf, CONF_sshbug_plainpw1) == AUTO &&
(!strcmp(imp, "Cisco-1.25") || !strcmp(imp, "OSU_1.4alpha3")))) {
/*
* These versions need a plain password sent; they can't
* handle having a null and a random length of data after
* the password.
*/
s->remote_bugs |= BUG_NEEDS_SSH1_PLAIN_PASSWORD;
bpp_logevent(("We believe remote version needs a "
"plain SSH-1 password"));
}
if (conf_get_int(s->conf, CONF_sshbug_rsa1) == FORCE_ON ||
(conf_get_int(s->conf, CONF_sshbug_rsa1) == AUTO &&
(!strcmp(imp, "Cisco-1.25")))) {
/*
* These versions apparently have no clue whatever about
* RSA authentication and will panic and die if they see
* an AUTH_RSA message.
*/
s->remote_bugs |= BUG_CHOKES_ON_RSA;
bpp_logevent(("We believe remote version can't handle SSH-1 "
"RSA authentication"));
}
if (conf_get_int(s->conf, CONF_sshbug_hmac2) == FORCE_ON ||
(conf_get_int(s->conf, CONF_sshbug_hmac2) == AUTO &&
!wc_match("* VShell", imp) &&
(wc_match("2.1.0*", imp) || wc_match("2.0.*", imp) ||
wc_match("2.2.0*", imp) || wc_match("2.3.0*", imp) ||
wc_match("2.1 *", imp)))) {
/*
* These versions have the HMAC bug.
*/
s->remote_bugs |= BUG_SSH2_HMAC;
bpp_logevent(("We believe remote version has SSH-2 HMAC bug"));
}
if (conf_get_int(s->conf, CONF_sshbug_derivekey2) == FORCE_ON ||
(conf_get_int(s->conf, CONF_sshbug_derivekey2) == AUTO &&
!wc_match("* VShell", imp) &&
(wc_match("2.0.0*", imp) || wc_match("2.0.10*", imp) ))) {
/*
* These versions have the key-derivation bug (failing to
* include the literal shared secret in the hashes that
* generate the keys).
*/
s->remote_bugs |= BUG_SSH2_DERIVEKEY;
bpp_logevent(("We believe remote version has SSH-2 "
"key-derivation bug"));
}
if (conf_get_int(s->conf, CONF_sshbug_rsapad2) == FORCE_ON ||
(conf_get_int(s->conf, CONF_sshbug_rsapad2) == AUTO &&
(wc_match("OpenSSH_2.[5-9]*", imp) ||
wc_match("OpenSSH_3.[0-2]*", imp) ||
wc_match("mod_sftp/0.[0-8]*", imp) ||
wc_match("mod_sftp/0.9.[0-8]", imp)))) {
/*
* These versions have the SSH-2 RSA padding bug.
*/
s->remote_bugs |= BUG_SSH2_RSA_PADDING;
bpp_logevent(("We believe remote version has SSH-2 RSA padding bug"));
}
if (conf_get_int(s->conf, CONF_sshbug_pksessid2) == FORCE_ON ||
(conf_get_int(s->conf, CONF_sshbug_pksessid2) == AUTO &&
wc_match("OpenSSH_2.[0-2]*", imp))) {
/*
* These versions have the SSH-2 session-ID bug in
* public-key authentication.
*/
s->remote_bugs |= BUG_SSH2_PK_SESSIONID;
bpp_logevent(("We believe remote version has SSH-2 "
"public-key-session-ID bug"));
}
if (conf_get_int(s->conf, CONF_sshbug_rekey2) == FORCE_ON ||
(conf_get_int(s->conf, CONF_sshbug_rekey2) == AUTO &&
(wc_match("DigiSSH_2.0", imp) ||
wc_match("OpenSSH_2.[0-4]*", imp) ||
wc_match("OpenSSH_2.5.[0-3]*", imp) ||
wc_match("Sun_SSH_1.0", imp) ||
wc_match("Sun_SSH_1.0.1", imp) ||
/* All versions <= 1.2.6 (they changed their format in 1.2.7) */
wc_match("WeOnlyDo-*", imp)))) {
/*
* These versions have the SSH-2 rekey bug.
*/
s->remote_bugs |= BUG_SSH2_REKEY;
bpp_logevent(("We believe remote version has SSH-2 rekey bug"));
}
if (conf_get_int(s->conf, CONF_sshbug_maxpkt2) == FORCE_ON ||
(conf_get_int(s->conf, CONF_sshbug_maxpkt2) == AUTO &&
(wc_match("1.36_sshlib GlobalSCAPE", imp) ||
wc_match("1.36 sshlib: GlobalScape", imp)))) {
/*
* This version ignores our makpkt and needs to be throttled.
*/
s->remote_bugs |= BUG_SSH2_MAXPKT;
bpp_logevent(("We believe remote version ignores SSH-2 "
"maximum packet size"));
}
if (conf_get_int(s->conf, CONF_sshbug_ignore2) == FORCE_ON) {
/*
* Servers that don't support SSH2_MSG_IGNORE. Currently,
* none detected automatically.
*/
s->remote_bugs |= BUG_CHOKES_ON_SSH2_IGNORE;
bpp_logevent(("We believe remote version has SSH-2 ignore bug"));
}
if (conf_get_int(s->conf, CONF_sshbug_oldgex2) == FORCE_ON ||
(conf_get_int(s->conf, CONF_sshbug_oldgex2) == AUTO &&
(wc_match("OpenSSH_2.[235]*", imp)))) {
/*
* These versions only support the original (pre-RFC4419)
* SSH-2 GEX request, and disconnect with a protocol error if
* we use the newer version.
*/
s->remote_bugs |= BUG_SSH2_OLDGEX;
bpp_logevent(("We believe remote version has outdated SSH-2 GEX"));
}
if (conf_get_int(s->conf, CONF_sshbug_winadj) == FORCE_ON) {
/*
* Servers that don't support our winadj request for one
* reason or another. Currently, none detected automatically.
*/
s->remote_bugs |= BUG_CHOKES_ON_WINADJ;
bpp_logevent(("We believe remote version has winadj bug"));
}
if (conf_get_int(s->conf, CONF_sshbug_chanreq) == FORCE_ON ||
(conf_get_int(s->conf, CONF_sshbug_chanreq) == AUTO &&
(wc_match("OpenSSH_[2-5].*", imp) ||
wc_match("OpenSSH_6.[0-6]*", imp) ||
wc_match("dropbear_0.[2-4][0-9]*", imp) ||
wc_match("dropbear_0.5[01]*", imp)))) {
/*
* These versions have the SSH-2 channel request bug.
* OpenSSH 6.7 and above do not:
* https://bugzilla.mindrot.org/show_bug.cgi?id=1818
* dropbear_0.52 and above do not:
* https://secure.ucc.asn.au/hg/dropbear/rev/cd02449b709c
*/
s->remote_bugs |= BUG_SENDS_LATE_REQUEST_REPLY;
bpp_logevent(("We believe remote version has SSH-2 "
"channel request bug"));
}
}
const char *ssh_verstring_get_remote(BinaryPacketProtocol *bpp)
{
struct ssh_verstring_state *s =
container_of(bpp, struct ssh_verstring_state, bpp);
return s->vstring;
}
const char *ssh_verstring_get_local(BinaryPacketProtocol *bpp)
{
struct ssh_verstring_state *s =
container_of(bpp, struct ssh_verstring_state, bpp);
return s->our_vstring;
}
int ssh_verstring_get_bugs(BinaryPacketProtocol *bpp)
{
struct ssh_verstring_state *s =
container_of(bpp, struct ssh_verstring_state, bpp);
return s->remote_bugs;
}
static void ssh_verstring_queue_disconnect(BinaryPacketProtocol *bpp,
const char *msg, int category)
{
/* No way to send disconnect messages at this stage of the protocol! */
}
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