Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * auth-sasl.c
4 : * Routines to handle authentication via SASL
5 : *
6 : * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
7 : * Portions Copyright (c) 1994, Regents of the University of California
8 : *
9 : *
10 : * IDENTIFICATION
11 : * src/backend/libpq/auth-sasl.c
12 : *
13 : *-------------------------------------------------------------------------
14 : */
15 :
16 : #include "postgres.h"
17 :
18 : #include "libpq/auth.h"
19 : #include "libpq/libpq.h"
20 : #include "libpq/pqformat.h"
21 : #include "libpq/sasl.h"
22 :
23 : /*
24 : * Maximum accepted size of SASL messages.
25 : *
26 : * The messages that the server or libpq generate are much smaller than this,
27 : * but have some headroom.
28 : */
29 : #define PG_MAX_SASL_MESSAGE_LENGTH 1024
30 :
31 : /*
32 : * Perform a SASL exchange with a libpq client, using a specific mechanism
33 : * implementation.
34 : *
35 : * shadow_pass is an optional pointer to the stored secret of the role
36 : * authenticated, from pg_authid.rolpassword. For mechanisms that use
37 : * shadowed passwords, a NULL pointer here means that an entry could not
38 : * be found for the role (or the user does not exist), and the mechanism
39 : * should fail the authentication exchange.
40 : *
41 : * Mechanisms must take care not to reveal to the client that a user entry
42 : * does not exist; ideally, the external failure mode is identical to that
43 : * of an incorrect password. Mechanisms may instead use the logdetail
44 : * output parameter to internally differentiate between failure cases and
45 : * assist debugging by the server admin.
46 : *
47 : * A mechanism is not required to utilize a shadow entry, or even a password
48 : * system at all; for these cases, shadow_pass may be ignored and the caller
49 : * should just pass NULL.
50 : */
51 : int
52 100 : CheckSASLAuth(const pg_be_sasl_mech *mech, Port *port, char *shadow_pass,
53 : const char **logdetail)
54 : {
55 : StringInfoData sasl_mechs;
56 : int mtype;
57 : StringInfoData buf;
58 100 : void *opaq = NULL;
59 100 : char *output = NULL;
60 100 : int outputlen = 0;
61 : const char *input;
62 : int inputlen;
63 : int result;
64 : bool initial;
65 :
66 : /*
67 : * Send the SASL authentication request to user. It includes the list of
68 : * authentication mechanisms that are supported.
69 : */
70 100 : initStringInfo(&sasl_mechs);
71 :
72 100 : mech->get_mechanisms(port, &sasl_mechs);
73 : /* Put another '\0' to mark that list is finished. */
74 100 : appendStringInfoChar(&sasl_mechs, '\0');
75 :
76 100 : sendAuthRequest(port, AUTH_REQ_SASL, sasl_mechs.data, sasl_mechs.len);
77 100 : pfree(sasl_mechs.data);
78 :
79 : /*
80 : * Loop through SASL message exchange. This exchange can consist of
81 : * multiple messages sent in both directions. First message is always
82 : * from the client. All messages from client to server are password
83 : * packets (type 'p').
84 : */
85 100 : initial = true;
86 : do
87 : {
88 178 : pq_startmsgread();
89 178 : mtype = pq_getbyte();
90 178 : if (mtype != PqMsg_SASLResponse)
91 : {
92 : /* Only log error if client didn't disconnect. */
93 22 : if (mtype != EOF)
94 : {
95 0 : ereport(ERROR,
96 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
97 : errmsg("expected SASL response, got message type %d",
98 : mtype)));
99 : }
100 : else
101 22 : return STATUS_EOF;
102 : }
103 :
104 : /* Get the actual SASL message */
105 156 : initStringInfo(&buf);
106 156 : if (pq_getmessage(&buf, PG_MAX_SASL_MESSAGE_LENGTH))
107 : {
108 : /* EOF - pq_getmessage already logged error */
109 0 : pfree(buf.data);
110 0 : return STATUS_ERROR;
111 : }
112 :
113 156 : elog(DEBUG4, "processing received SASL response of length %d", buf.len);
114 :
115 : /*
116 : * The first SASLInitialResponse message is different from the others.
117 : * It indicates which SASL mechanism the client selected, and contains
118 : * an optional Initial Client Response payload. The subsequent
119 : * SASLResponse messages contain just the SASL payload.
120 : */
121 156 : if (initial)
122 : {
123 : const char *selected_mech;
124 :
125 78 : selected_mech = pq_getmsgrawstring(&buf);
126 :
127 : /*
128 : * Initialize the status tracker for message exchanges.
129 : *
130 : * If the user doesn't exist, or doesn't have a valid password, or
131 : * it's expired, we still go through the motions of SASL
132 : * authentication, but tell the authentication method that the
133 : * authentication is "doomed". That is, it's going to fail, no
134 : * matter what.
135 : *
136 : * This is because we don't want to reveal to an attacker what
137 : * usernames are valid, nor which users have a valid password.
138 : */
139 78 : opaq = mech->init(port, selected_mech, shadow_pass);
140 :
141 78 : inputlen = pq_getmsgint(&buf, 4);
142 78 : if (inputlen == -1)
143 0 : input = NULL;
144 : else
145 78 : input = pq_getmsgbytes(&buf, inputlen);
146 :
147 78 : initial = false;
148 : }
149 : else
150 : {
151 78 : inputlen = buf.len;
152 78 : input = pq_getmsgbytes(&buf, buf.len);
153 : }
154 156 : pq_getmsgend(&buf);
155 :
156 : /*
157 : * The StringInfo guarantees that there's a \0 byte after the
158 : * response.
159 : */
160 : Assert(input == NULL || input[inputlen] == '\0');
161 :
162 : /*
163 : * Hand the incoming message to the mechanism implementation.
164 : */
165 156 : result = mech->exchange(opaq, input, inputlen,
166 : &output, &outputlen,
167 : logdetail);
168 :
169 : /* input buffer no longer used */
170 156 : pfree(buf.data);
171 :
172 156 : if (output)
173 : {
174 : /*
175 : * PG_SASL_EXCHANGE_FAILURE with some output is forbidden by SASL.
176 : * Make sure here that the mechanism used got that right.
177 : */
178 144 : if (result == PG_SASL_EXCHANGE_FAILURE)
179 0 : elog(ERROR, "output message found after SASL exchange failure");
180 :
181 : /*
182 : * Negotiation generated data to be sent to the client.
183 : */
184 144 : elog(DEBUG4, "sending SASL challenge of length %d", outputlen);
185 :
186 144 : if (result == PG_SASL_EXCHANGE_SUCCESS)
187 66 : sendAuthRequest(port, AUTH_REQ_SASL_FIN, output, outputlen);
188 : else
189 78 : sendAuthRequest(port, AUTH_REQ_SASL_CONT, output, outputlen);
190 :
191 144 : pfree(output);
192 : }
193 156 : } while (result == PG_SASL_EXCHANGE_CONTINUE);
194 :
195 : /* Oops, Something bad happened */
196 78 : if (result != PG_SASL_EXCHANGE_SUCCESS)
197 : {
198 12 : return STATUS_ERROR;
199 : }
200 :
201 66 : return STATUS_OK;
202 : }
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