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putty-source/proxy/http.c
Simon Tatham a2ff884512 Richer data type for interactive prompt results. 
All the seat functions that request an interactive prompt of some kind
to the user - both the main seat_get_userpass_input and the various
confirmation dialogs for things like host keys - were using a simple
int return value, with the general semantics of 0 = "fail", 1 =
"proceed" (and in the case of seat_get_userpass_input, answers to the
prompts were provided), and -1 = "request in progress, wait for a
callback".

In this commit I change all those functions' return types to a new
struct called SeatPromptResult, whose primary field is an enum
replacing those simple integer values.

The main purpose is that the enum has not three but _four_ values: the
"fail" result has been split into 'user abort' and 'software abort'.
The distinction is that a user abort occurs as a result of an
interactive UI action, such as the user clicking 'cancel' in a dialog
box or hitting ^D or ^C at a terminal password prompt - and therefore,
there's no need to display an error message telling the user that the
interactive operation has failed, because the user already knows,
because they _did_ it. 'Software abort' is from any other cause, where
PuTTY is the first to know there was a problem, and has to tell the
user.

We already had this 'user abort' vs 'software abort' distinction in
other parts of the code - the SSH backend has separate termination
functions which protocol layers can call. But we assumed that any
failure from an interactive prompt request fell into the 'user abort'
category, which is not true. A couple of examples: if you configure a
host key fingerprint in your saved session via the SSH > Host keys
pane, and the server presents a host key that doesn't match it, then
verify_ssh_host_key would report that the user had aborted the
connection, and feel no need to tell the user what had gone wrong!
Similarly, if a password provided on the command line was not
accepted, then (after I fixed the semantics of that in the previous
commit) the same wrong handling would occur.

So now, those Seat prompt functions too can communicate whether the
user or the software originated a connection abort. And in the latter
case, we also provide an error message to present to the user. Result:
in those two example cases (and others), error messages should no
longer go missing.

Implementation note: to avoid the hassle of having the error message
in a SeatPromptResult being a dynamically allocated string (and hence,
every recipient of one must always check whether it's non-NULL and
free it on every exit path, plus being careful about copying the
struct around), I've instead arranged that the structure contains a
function pointer and a couple of parameters, so that the string form
of the message can be constructed on demand. That way, the only users
who need to free it are the ones who actually _asked_ for it in the
first place, which is a much smaller set.

(This is one of the rare occasions that I regret not having C++'s
extra features available in this code base - a unique_ptr or
shared_ptr to a string would have been just the thing here, and the
compiler would have done all the hard work for me of remembering where
to insert the frees!)
2021-12-28 18:08:31 +00:00

706 lines
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/*
* HTTP CONNECT proxy negotiation.
*/
#include "putty.h"
#include "network.h"
#include "proxy.h"
#include "sshcr.h"
static bool read_line(bufchain *input, strbuf *output, bool is_header)
{
char c;
while (bufchain_try_fetch(input, &c, 1)) {
if (is_header && output->len > 0 &&
output->s[output->len - 1] == '\n') {
/*
* A newline terminates the header, provided we're sure it
* is _not_ followed by a space or a tab.
*/
if (c != ' ' && c != '\t')
goto done; /* we have a complete header line */
} else {
put_byte(output, c);
bufchain_consume(input, 1);
if (!is_header && output->len > 0 &&
output->s[output->len - 1] == '\n') {
/* If we're looking for just a line, not an HTTP
* header, then any newline terminates it. */
goto done;
}
}
}
return false;
done:
strbuf_chomp(output, '\n');
strbuf_chomp(output, '\r');
return true;
}
/* Types of HTTP authentication, in preference order. */
typedef enum HttpAuthType {
AUTH_ERROR, /* if an HttpAuthDetails was never satisfactorily filled in */
AUTH_NONE, /* if no auth header is seen, assume no auth required */
AUTH_BASIC, /* username + password sent in clear (only keyless base64) */
AUTH_DIGEST, /* cryptographic hash, most preferred if available */
} HttpAuthType;
typedef struct HttpAuthDetails {
HttpAuthType auth_type;
bool digest_nonce_was_stale;
HttpDigestHash digest_hash;
strbuf *realm, *nonce, *opaque, *error;
bool got_opaque;
bool hash_username;
} HttpAuthDetails;
typedef struct HttpProxyNegotiator {
int crLine;
strbuf *response, *header, *token;
int http_status_pos;
size_t header_pos;
strbuf *username, *password;
int http_status;
bool connection_close;
HttpAuthDetails *next_auth;
bool try_auth_from_conf;
strbuf *uri;
uint32_t nonce_count;
prompts_t *prompts;
int username_prompt_index, password_prompt_index;
size_t content_length;
ProxyNegotiator pn;
} HttpProxyNegotiator;
static inline HttpAuthDetails *auth_error(HttpAuthDetails *d,
const char *fmt, ...)
{
d->auth_type = AUTH_ERROR;
put_fmt(d->error, "Unable to parse auth header from HTTP proxy");
if (fmt) {
va_list ap;
va_start(ap, fmt);
put_datalit(d->error, ": ");
put_fmtv(d->error, fmt, ap);
va_end(ap);
}
return d;
}
static HttpAuthDetails *http_auth_details_new(void)
{
HttpAuthDetails *d = snew(HttpAuthDetails);
memset(d, 0, sizeof(*d));
d->realm = strbuf_new();
d->nonce = strbuf_new();
d->opaque = strbuf_new();
d->error = strbuf_new();
return d;
}
static void http_auth_details_free(HttpAuthDetails *d)
{
strbuf_free(d->realm);
strbuf_free(d->nonce);
strbuf_free(d->opaque);
strbuf_free(d->error);
sfree(d);
}
static ProxyNegotiator *proxy_http_new(const ProxyNegotiatorVT *vt)
{
HttpProxyNegotiator *s = snew(HttpProxyNegotiator);
memset(s, 0, sizeof(*s));
s->pn.vt = vt;
s->response = strbuf_new();
s->header = strbuf_new();
s->token = strbuf_new();
s->username = strbuf_new();
s->password = strbuf_new_nm();
s->uri = strbuf_new();
s->nonce_count = 0;
/*
* Always start with a CONNECT request containing no auth. If the
* proxy rejects that, it will tell us what kind of auth it would
* prefer.
*/
s->next_auth = http_auth_details_new();
s->next_auth->auth_type = AUTH_NONE;
return &s->pn;
}
static void proxy_http_free(ProxyNegotiator *pn)
{
HttpProxyNegotiator *s = container_of(pn, HttpProxyNegotiator, pn);
strbuf_free(s->response);
strbuf_free(s->header);
strbuf_free(s->token);
strbuf_free(s->username);
strbuf_free(s->password);
strbuf_free(s->uri);
http_auth_details_free(s->next_auth);
if (s->prompts)
free_prompts(s->prompts);
sfree(s);
}
#define HTTP_HEADER_LIST(X) \
X(HDR_CONNECTION, "Connection") \
X(HDR_CONTENT_LENGTH, "Content-Length") \
X(HDR_PROXY_AUTHENTICATE, "Proxy-Authenticate") \
/* end of list */
typedef enum HttpHeader {
#define ENUM_DEF(id, string) id,
HTTP_HEADER_LIST(ENUM_DEF)
#undef ENUM_DEF
HDR_UNKNOWN
} HttpHeader;
static inline bool is_whitespace(char c)
{
return (c == ' ' || c == '\t' || c == '\n');
}
static inline bool is_separator(char c)
{
return (c == '(' || c == ')' || c == '<' || c == '>' || c == '@' ||
c == ',' || c == ';' || c == ':' || c == '\\' || c == '"' ||
c == '/' || c == '[' || c == ']' || c == '?' || c == '=' ||
c == '{' || c == '}');
}
#define HTTP_SEPARATORS
static bool get_end_of_header(HttpProxyNegotiator *s)
{
size_t pos = s->header_pos;
while (pos < s->header->len && is_whitespace(s->header->s[pos]))
pos++;
if (pos == s->header->len) {
s->header_pos = pos;
return true;
}
return false;
}
static bool get_token(HttpProxyNegotiator *s)
{
size_t pos = s->header_pos;
while (pos < s->header->len && is_whitespace(s->header->s[pos]))
pos++;
if (pos == s->header->len)
return false; /* end of string */
if (is_separator(s->header->s[pos]))
return false;
strbuf_clear(s->token);
while (pos < s->header->len &&
!is_whitespace(s->header->s[pos]) &&
!is_separator(s->header->s[pos]))
put_byte(s->token, s->header->s[pos++]);
s->header_pos = pos;
return true;
}
static bool get_separator(HttpProxyNegotiator *s, char sep)
{
size_t pos = s->header_pos;
while (pos < s->header->len && is_whitespace(s->header->s[pos]))
pos++;
if (pos == s->header->len)
return false; /* end of string */
if (s->header->s[pos] != sep)
return false;
s->header_pos = ++pos;
return true;
}
static bool get_quoted_string(HttpProxyNegotiator *s)
{
size_t pos = s->header_pos;
while (pos < s->header->len && is_whitespace(s->header->s[pos]))
pos++;
if (pos == s->header->len)
return false; /* end of string */
if (s->header->s[pos] != '"')
return false;
pos++;
strbuf_clear(s->token);
while (pos < s->header->len && s->header->s[pos] != '"') {
if (s->header->s[pos] == '\\') {
/* Backslash makes the next char literal, even if it's " or \ */
pos++;
if (pos == s->header->len)
return false; /* unexpected end of string */
}
put_byte(s->token, s->header->s[pos++]);
}
if (pos == s->header->len)
return false; /* no closing quote */
pos++;
s->header_pos = pos;
return true;
}
static HttpAuthDetails *parse_http_auth_header(HttpProxyNegotiator *s)
{
HttpAuthDetails *d = http_auth_details_new();
/* Default hash for HTTP Digest is MD5, if none specified explicitly */
d->digest_hash = HTTP_DIGEST_MD5;
if (!get_token(s))
return auth_error(d, "parse error");
if (!stricmp(s->token->s, "Basic")) {
/* For Basic authentication, we don't need anything else. The
* realm string is not required for the protocol. */
d->auth_type = AUTH_BASIC;
return d;
}
if (!stricmp(s->token->s, "Digest")) {
/* Parse all the additional parts of the Digest header. */
if (!http_digest_available)
return auth_error(d, "Digest authentication not supported");
/* Parse the rest of the Digest header */
while (true) {
if (!get_token(s))
return auth_error(d, "parse error in Digest header");
if (!stricmp(s->token->s, "realm")) {
if (!get_separator(s, '=') ||
!get_quoted_string(s))
return auth_error(d, "parse error in Digest realm field");
put_datapl(d->realm, ptrlen_from_strbuf(s->token));
} else if (!stricmp(s->token->s, "nonce")) {
if (!get_separator(s, '=') ||
!get_quoted_string(s))
return auth_error(d, "parse error in Digest nonce field");
put_datapl(d->nonce, ptrlen_from_strbuf(s->token));
} else if (!stricmp(s->token->s, "opaque")) {
if (!get_separator(s, '=') ||
!get_quoted_string(s))
return auth_error(d, "parse error in Digest opaque field");
put_datapl(d->opaque,
ptrlen_from_strbuf(s->token));
d->got_opaque = true;
} else if (!stricmp(s->token->s, "stale")) {
if (!get_separator(s, '=') ||
!get_token(s))
return auth_error(d, "parse error in Digest stale field");
d->digest_nonce_was_stale = !stricmp(
s->token->s, "true");
} else if (!stricmp(s->token->s, "userhash")) {
if (!get_separator(s, '=') ||
!get_token(s))
return auth_error(d, "parse error in Digest userhash "
"field");
d->hash_username = !stricmp(s->token->s, "true");
} else if (!stricmp(s->token->s, "algorithm")) {
if (!get_separator(s, '=') ||
!get_token(s))
return auth_error(d, "parse error in Digest algorithm "
"field");
bool found = false;
size_t i;
for (i = 0; i < N_HTTP_DIGEST_HASHES; i++) {
if (!stricmp(s->token->s, httphashnames[i])) {
found = true;
break;
}
}
if (!found) {
/* We don't even recognise the name */
return auth_error(d, "Digest hash algorithm '%s' not "
"recognised", s->token->s);
}
if (!httphashaccepted[i]) {
/* We do recognise the name but we
* don't like it (see comment in cproxy.h) */
return auth_error(d, "Digest hash algorithm '%s' not "
"supported", s->token->s);
}
d->digest_hash = i;
} else if (!stricmp(s->token->s, "qop")) {
if (!get_separator(s, '=') ||
!get_quoted_string(s))
return auth_error(d, "parse error in Digest qop field");
if (stricmp(s->token->s, "auth"))
return auth_error(d, "quality-of-protection type '%s' not "
"supported", s->token->s);
} else {
/* Ignore any other auth-param */
if (!get_separator(s, '=') ||
(!get_quoted_string(s) && !get_token(s)))
return auth_error(d, "parse error in Digest header");
}
if (get_end_of_header(s))
break;
if (!get_separator(s, ','))
return auth_error(d, "parse error in Digest header");
}
d->auth_type = AUTH_DIGEST;
return d;
}
return auth_error(d, "authentication type '%s' not supported",
s->token->s);
}
static void proxy_http_process_queue(ProxyNegotiator *pn)
{
HttpProxyNegotiator *s = container_of(pn, HttpProxyNegotiator, pn);
crBegin(s->crLine);
/*
* Initialise our username and password strbufs from the Conf.
*/
put_dataz(s->username, conf_get_str(pn->ps->conf, CONF_proxy_username));
put_dataz(s->password, conf_get_str(pn->ps->conf, CONF_proxy_password));
if (s->username->len || s->password->len)
s->try_auth_from_conf = true;
/*
* Set up the host:port string we're trying to connect to, also
* used as the URI string in HTTP Digest auth.
*/
{
char dest[512];
sk_getaddr(pn->ps->remote_addr, dest, lenof(dest));
put_fmt(s->uri, "%s:%d", dest, pn->ps->remote_port);
}
while (true) {
/*
* Standard prefix for the HTTP CONNECT request.
*/
put_fmt(pn->output,
"CONNECT %s HTTP/1.1\r\n"
"Host: %s\r\n", s->uri->s, s->uri->s);
/*
* Add an auth header, if we're planning to this time round.
*/
if (s->next_auth->auth_type == AUTH_BASIC) {
put_datalit(pn->output, "Proxy-Authorization: Basic ");
strbuf *base64_input = strbuf_new_nm();
put_datapl(base64_input, ptrlen_from_strbuf(s->username));
put_byte(base64_input, ':');
put_datapl(base64_input, ptrlen_from_strbuf(s->password));
char base64_output[4];
for (size_t i = 0, e = base64_input->len; i < e; i += 3) {
base64_encode_atom(base64_input->u + i,
e-i > 3 ? 3 : e-i, base64_output);
put_data(pn->output, base64_output, 4);
}
strbuf_free(base64_input);
smemclr(base64_output, sizeof(base64_output));
put_datalit(pn->output, "\r\n");
} else if (s->next_auth->auth_type == AUTH_DIGEST) {
put_datalit(pn->output, "Proxy-Authorization: Digest ");
/* If we have a fresh nonce, reset the
* nonce count. Otherwise, keep incrementing it. */
if (!ptrlen_eq_ptrlen(ptrlen_from_strbuf(s->token),
ptrlen_from_strbuf(s->next_auth->nonce)))
s->nonce_count = 0;
http_digest_response(BinarySink_UPCAST(pn->output),
ptrlen_from_strbuf(s->username),
ptrlen_from_strbuf(s->password),
ptrlen_from_strbuf(s->next_auth->realm),
PTRLEN_LITERAL("CONNECT"),
ptrlen_from_strbuf(s->uri),
PTRLEN_LITERAL("auth"),
ptrlen_from_strbuf(s->next_auth->nonce),
(s->next_auth->got_opaque ?
ptrlen_from_strbuf(s->next_auth->opaque) :
make_ptrlen(NULL, 0)),
++s->nonce_count, s->next_auth->digest_hash,
s->next_auth->hash_username);
put_datalit(pn->output, "\r\n");
}
/*
* Blank line to terminate the HTTP request.
*/
put_datalit(pn->output, "\r\n");
crReturnV;
s->content_length = 0;
s->connection_close = false;
/*
* Read and parse the HTTP status line, and check if it's a 2xx
* for success.
*/
strbuf_clear(s->response);
crMaybeWaitUntilV(read_line(pn->input, s->response, false));
{
int maj_ver, min_ver, n_scanned;
n_scanned = sscanf(
s->response->s, "HTTP/%d.%d %n%d",
&maj_ver, &min_ver, &s->http_status_pos, &s->http_status);
if (n_scanned < 3) {
pn->error = dupstr("HTTP response was absent or malformed");
crStopV;
}
if (maj_ver < 1 && (maj_ver == 1 && min_ver < 1)) {
/* Before HTTP/1.1, connections close by default */
s->connection_close = true;
}
}
if (s->http_status == 407) {
/*
* If this is going to be an auth request, we expect to
* see at least one Proxy-Authorization header offering us
* auth options. Start by preloading s->next_auth with a
* fallback error message, which will be used if nothing
* better is available.
*/
http_auth_details_free(s->next_auth);
s->next_auth = http_auth_details_new();
auth_error(s->next_auth, "no Proxy-Authorization header seen in "
"HTTP 407 Proxy Authentication Required response");
}
/*
* Read the HTTP response header section.
*/
do {
strbuf_clear(s->header);
crMaybeWaitUntilV(read_line(pn->input, s->header, true));
s->header_pos = 0;
if (!get_token(s)) {
/* Possibly we ought to panic if we see an HTTP header
* we can't make any sense of at all? But whatever,
* ignore it and hope the next one makes more sense */
continue;
}
/* Parse the header name */
HttpHeader hdr = HDR_UNKNOWN;
{
#define CHECK_HEADER(id, string) \
if (!stricmp(s->token->s, string)) hdr = id;
HTTP_HEADER_LIST(CHECK_HEADER);
#undef CHECK_HEADER
}
if (!get_separator(s, ':'))
continue;
if (hdr == HDR_CONTENT_LENGTH) {
if (!get_token(s))
continue;
s->content_length = strtoumax(s->token->s, NULL, 10);
} else if (hdr == HDR_CONNECTION) {
if (!get_token(s))
continue;
if (!stricmp(s->token->s, "close"))
s->connection_close = true;
else if (!stricmp(s->token->s, "keep-alive"))
s->connection_close = false;
} else if (hdr == HDR_PROXY_AUTHENTICATE) {
HttpAuthDetails *auth = parse_http_auth_header(s);
/*
* See if we prefer this set of auth details to the
* previous one we had (either from a previous auth
* header, or the fallback when no auth header is
* provided at all).
*/
bool change;
if (auth->auth_type != s->next_auth->auth_type) {
/* Use the preference order implied by the enum */
change = auth->auth_type > s->next_auth->auth_type;
} else if (auth->auth_type == AUTH_DIGEST &&
auth->digest_hash != s->next_auth->digest_hash) {
/* Choose based on the hash functions */
change = auth->digest_hash > s->next_auth->digest_hash;
} else {
/*
* If in doubt, go with the later one of the
* headers.
*
* The main reason for this is so that an error in
* interpreting an auth header will supersede the
* default error we preload saying 'no header
* found', because that would be a particularly
* bad error to report if there _was_ one.
*
* But we're in a tie-breaking situation by now,
* so there's no other reason to choose - we might
* as well apply the same policy everywhere else
* too.
*/
change = true;
}
if (change) {
http_auth_details_free(s->next_auth);
s->next_auth = auth;
} else {
http_auth_details_free(auth);
}
}
} while (s->header->len > 0);
/* Read and ignore the entire response document */
crMaybeWaitUntilV(bufchain_try_consume(
pn->input, s->content_length));
if (200 <= s->http_status && s->http_status < 300) {
/* Any 2xx HTTP response means we're done */
goto authenticated;
} else if (s->http_status == 407) {
/* 407 is Proxy Authentication Required, which we may be
* able to do something about. */
if (s->connection_close) {
pn->error = dupprintf("HTTP proxy closed connection after "
"asking for authentication");
crStopV;
}
/* If the best we can do is report some kind of error from
* a Proxy-Auth header (or an error saying there wasn't
* one at all), and no successful parsing of an auth
* header superseded that, then just throw that error and
* die. */
if (s->next_auth->auth_type == AUTH_ERROR) {
pn->error = dupstr(s->next_auth->error->s);
crStopV;
}
/* If we have auth details from the Conf and haven't tried
* them yet, that's our first step. */
if (s->try_auth_from_conf) {
s->try_auth_from_conf = false;
continue;
}
/* If the server sent us stale="true" in a Digest auth
* header, that means we _don't_ need to request a new
* password yet; just try again with the existing details
* and the fresh nonce it sent us. */
if (s->next_auth->digest_nonce_was_stale)
continue;
/* Either we never had a password in the first place, or
* the one we already presented was rejected. We can only
* proceed from here if we have a way to ask the user
* questions. */
if (!pn->itr) {
pn->error = dupprintf("HTTP proxy requested authentication "
"which we do not have");
crStopV;
}
/*
* Send some prompts to the user. We'll assume the
* password is always required (since it's just been
* rejected, even if we did send one before), and we'll
* prompt for the username only if we don't have one from
* the Conf.
*/
s->prompts = proxy_new_prompts(pn->ps);
s->prompts->to_server = true;
s->prompts->from_server = false;
s->prompts->name = dupstr("HTTP proxy authentication");
if (!s->username->len) {
s->username_prompt_index = s->prompts->n_prompts;
add_prompt(s->prompts, dupstr("Proxy username: "), true);
} else {
s->username_prompt_index = -1;
}
s->password_prompt_index = s->prompts->n_prompts;
add_prompt(s->prompts, dupstr("Proxy password: "), false);
while (true) {
SeatPromptResult spr = seat_get_userpass_input(
interactor_announce(pn->itr), s->prompts);
if (spr.kind == SPRK_OK) {
break;
} else if (spr_is_abort(spr)) {
proxy_spr_abort(pn, spr);
crStopV;
}
crReturnV;
}
if (s->username_prompt_index != -1) {
strbuf_clear(s->username);
put_dataz(s->username,
prompt_get_result_ref(
s->prompts->prompts[s->username_prompt_index]));
}
strbuf_clear(s->password);
put_dataz(s->password,
prompt_get_result_ref(
s->prompts->prompts[s->password_prompt_index]));
free_prompts(s->prompts);
s->prompts = NULL;
} else {
/* Any other HTTP response is treated as permanent failure */
pn->error = dupprintf("HTTP response %s",
s->response->s + s->http_status_pos);
crStopV;
}
}
authenticated:
/*
* Success! Hand over to the main connection.
*/
pn->done = true;
crFinishV;
}
const struct ProxyNegotiatorVT http_proxy_negotiator_vt = {
.new = proxy_http_new,
.free = proxy_http_free,
.process_queue = proxy_http_process_queue,
.type = "HTTP",
};
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