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Check channel binding flag at end of SCRAM exchange

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We need to check whether the channel-binding flag encoded in the
client-final-message is the same one sent in the client-first-message.

Reviewed-by: Michael Paquier <michael.paquier@gmail.com>
This commit is contained in:
Peter Eisentraut 2017-11-22 14:02:57 -05:00
parent 143b54d21d
commit 86ab28fbd1
2 changed files with 12 additions and 3 deletions
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11
src/backend/libpq/auth-scram.c
View File

@ -110,6 +110,7 @@ typedef struct
const char *username; /* username from startup packet */
char cbind_flag;
bool ssl_in_use;
const char *tls_finished_message;
size_t tls_finished_len;
@ -788,6 +789,7 @@ read_client_first_message(scram_state *state, char *input)
* Read gs2-cbind-flag. (For details see also RFC 5802 Section 6 "Channel
* Binding".)
*/
state->cbind_flag = *input;
switch (*input)
{
case 'n':
@ -1111,6 +1113,8 @@ read_client_final_message(scram_state *state, char *input)
char *b64_message;
int b64_message_len;
Assert(state->cbind_flag == 'p');
/*
* Fetch data appropriate for channel binding type
*/
@ -1155,10 +1159,11 @@ read_client_final_message(scram_state *state, char *input)
/*
* If we are not using channel binding, the binding data is expected
* to always be "biws", which is "n,," base64-encoded, or "eSws",
* which is "y,,".
* which is "y,,". We also have to check whether the flag is the same
* one that the client originally sent.
*/
if (strcmp(channel_binding, "biws") != 0 &&
strcmp(channel_binding, "eSws") != 0)
if (!(strcmp(channel_binding, "biws") == 0 && state->cbind_flag == 'n') &&
!(strcmp(channel_binding, "eSws") == 0 && state->cbind_flag == 'y'))
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
(errmsg("unexpected SCRAM channel-binding attribute in client-final-message"))));

4
src/interfaces/libpq/fe-auth-scram.c
View File

@ -437,6 +437,10 @@ build_client_final_message(fe_scram_state *state, PQExpBuffer errormessage)
/*
* Construct client-final-message-without-proof. We need to remember it
* for verifying the server proof in the final step of authentication.
*
* The channel binding flag handling (p/y/n) must be consistent with
* build_client_first_message(), because the server will check that it's
* the same flag both times.
*/
if (strcmp(state->sasl_mechanism, SCRAM_SHA256_PLUS_NAME) == 0)
{