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Richer data type for interactive prompt results.

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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!)
This commit is contained in:
Simon Tatham
2021-12-28 17:52:00 +00:00
parent a82ab70b0b
commit a2ff884512
51 changed files with 648 additions and 372 deletions
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44
ssh/transport2.c
View File

@ -97,7 +97,7 @@ static void ssh2_transport_gss_update(struct ssh2_transport_state *s,
static bool ssh2_transport_timer_update(struct ssh2_transport_state *s,
unsigned long rekey_time);
static int ssh2_transport_confirm_weak_crypto_primitive(
static SeatPromptResult ssh2_transport_confirm_weak_crypto_primitive(
struct ssh2_transport_state *s, const char *type, const char *name,
const void *alg);
@ -1265,11 +1265,11 @@ static void ssh2_transport_process_queue(PacketProtocolLayer *ppl)
}
if (s->warn_kex) {
s->dlgret = ssh2_transport_confirm_weak_crypto_primitive(
s->spr = ssh2_transport_confirm_weak_crypto_primitive(
s, "key-exchange algorithm", s->kex_alg->name, s->kex_alg);
crMaybeWaitUntilV(s->dlgret >= 0);
if (s->dlgret == 0) {
ssh_user_close(s->ppl.ssh, "User aborted at kex warning");
crMaybeWaitUntilV(s->spr.kind != SPRK_INCOMPLETE);
if (spr_is_abort(s->spr)) {
ssh_spr_close(s->ppl.ssh, s->spr, "kex warning");
return;
}
}
@ -1312,42 +1312,42 @@ static void ssh2_transport_process_queue(PacketProtocolLayer *ppl)
if (betteralgs) {
/* Use the special warning prompt that lets us provide
* a list of better algorithms */
s->dlgret = seat_confirm_weak_cached_hostkey(
s->spr = seat_confirm_weak_cached_hostkey(
ppl_get_iseat(&s->ppl), s->hostkey_alg->ssh_id, betteralgs,
ssh2_transport_dialog_callback, s);
sfree(betteralgs);
} else {
/* If none exist, use the more general 'weak crypto'
* warning prompt */
s->dlgret = ssh2_transport_confirm_weak_crypto_primitive(
s->spr = ssh2_transport_confirm_weak_crypto_primitive(
s, "host key type", s->hostkey_alg->ssh_id,
s->hostkey_alg);
}
crMaybeWaitUntilV(s->dlgret >= 0);
if (s->dlgret == 0) {
ssh_user_close(s->ppl.ssh, "User aborted at host key warning");
crMaybeWaitUntilV(s->spr.kind != SPRK_INCOMPLETE);
if (spr_is_abort(s->spr)) {
ssh_spr_close(s->ppl.ssh, s->spr, "host key warning");
return;
}
}
if (s->warn_cscipher) {
s->dlgret = ssh2_transport_confirm_weak_crypto_primitive(
s->spr = ssh2_transport_confirm_weak_crypto_primitive(
s, "client-to-server cipher", s->out.cipher->ssh2_id,
s->out.cipher);
crMaybeWaitUntilV(s->dlgret >= 0);
if (s->dlgret == 0) {
ssh_user_close(s->ppl.ssh, "User aborted at cipher warning");
crMaybeWaitUntilV(s->spr.kind != SPRK_INCOMPLETE);
if (spr_is_abort(s->spr)) {
ssh_spr_close(s->ppl.ssh, s->spr, "cipher warning");
return;
}
}
if (s->warn_sccipher) {
s->dlgret = ssh2_transport_confirm_weak_crypto_primitive(
s->spr = ssh2_transport_confirm_weak_crypto_primitive(
s, "server-to-client cipher", s->in.cipher->ssh2_id,
s->in.cipher);
crMaybeWaitUntilV(s->dlgret >= 0);
if (s->dlgret == 0) {
ssh_user_close(s->ppl.ssh, "User aborted at cipher warning");
crMaybeWaitUntilV(s->spr.kind != SPRK_INCOMPLETE);
if (spr_is_abort(s->spr)) {
ssh_spr_close(s->ppl.ssh, s->spr, "cipher warning");
return;
}
}
@ -1815,10 +1815,10 @@ static bool ssh2_transport_timer_update(struct ssh2_transport_state *s,
return false;
}
void ssh2_transport_dialog_callback(void *vctx, int ret)
void ssh2_transport_dialog_callback(void *vctx, SeatPromptResult spr)
{
struct ssh2_transport_state *s = (struct ssh2_transport_state *)vctx;
s->dlgret = ret;
s->spr = spr;
ssh_ppl_process_queue(&s->ppl);
}
@ -2139,12 +2139,12 @@ static int weak_algorithm_compare(void *av, void *bv)
* tree234 s->weak_algorithms_consented_to to ensure we ask at most
* once about any given crypto primitive.
*/
static int ssh2_transport_confirm_weak_crypto_primitive(
static SeatPromptResult ssh2_transport_confirm_weak_crypto_primitive(
struct ssh2_transport_state *s, const char *type, const char *name,
const void *alg)
{
if (find234(s->weak_algorithms_consented_to, (void *)alg, NULL))
return 1;
return SPR_OK;
add234(s->weak_algorithms_consented_to, (void *)alg);
return seat_confirm_weak_crypto_primitive(