sendmail: support AUTH PLAIN in addition to AUTH LOGIN

Implement the -am argument to allow choosing an AUTH method.
For now only PLAIN and LOGIN are supported, but others can be added
easily in the future.

AUTH PLAIN required adding a new variant of encode_base64() capable of
handling NUL characters in the input string; the old function is now a
wrapper for the newer one.

function                                             old     new   delta
encode_n_base64                                        -     236    +236
sendmail_main                                       1199    1380    +181
packed_usage                                       32873   32877      +4
encode_base64                                        242      36    -206
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 2/1 up/down: 421/-206)          Total: 215 bytes

Signed-off-by: Raffaello D. Di Napoli <rafdev@dinapo.li>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 32 insertions, 8 deletions

diff --git a/mailutils/sendmail.c b/mailutils/sendmail.c
index 0170f2870..1dbaf595c 100644
--- a/mailutils/sendmail.c
+++ b/mailutils/sendmail.c
@@ -36,7 +36,9 @@
 //usage:     "\n                openssl s_client -quiet -tls1 -connect smtp.gmail.com:465"
 //usage:     "\n                        $SMTP_ANTISPAM_DELAY: seconds to wait after helper connect"
 //usage:     "\n        -S HOST[:PORT]  Server (default $SMTPHOST or 127.0.0.1)"
-//usage:     "\n        -amLOGIN        Log in using AUTH LOGIN (-amCRAM-MD5 not supported)"
+//usage:     "\n        -amLOGIN        Log in using AUTH LOGIN"
+//usage:     "\n        -amPLAIN        or AUTH PLAIN"
+//usage:     "\n                        (-amCRAM-MD5 not supported)"
 //usage:     "\n        -auUSER         Username for AUTH"
 //usage:     "\n        -apPASS         Password for AUTH"
 //usage:     "\n"
@@ -248,6 +250,10 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
                 OPT_S = 1 << 6,         // specify connection string
                 OPT_a = 1 << 7,         // authentication tokens
                 OPT_v = 1 << 8,         // verbosity
+        //--- from -am
+                OPT_am_mask = 3 << 14,  // AUTH method
+                OPT_am_login = 0 << 14, // AUTH LOGIN (default)
+                OPT_am_plain = 1 << 14, // AUTH PLAIN
         };
 
         // init global variables
@@ -286,9 +292,12 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
                         G.user = xstrdup(a+1);
                 if ('p' == a[0])
                         G.pass = xstrdup(a+1);
-                // N.B. we support only AUTH LOGIN so far
-                //if ('m' == a[0])
-                //      G.method = xstrdup(a+1);
+                if ('m' == a[0]) {
+                        if (strcasecmp("plain", a+1) == 0)
+                                opts |= OPT_am_plain;
+                        else if (strcasecmp("login", a+1) != 0)
+                                bb_error_msg_and_die("unsupported AUTH method %s", a+1);
+                }
         }
         // N.B. list == NULL here
         //bb_error_msg("OPT[%x] AU[%s], AP[%s], AM[%s], ARGV[%s]", opts, au, ap, am, *argv);
@@ -348,13 +357,28 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
 
         // perform authentication
         if (opts & OPT_a) {
-                smtp_check("AUTH LOGIN", 334);
                 // we must read credentials unless they are given via -a[up] options
                 if (!G.user || !G.pass)
                         get_cred_or_die(4);
-                encode_base64(NULL, G.user, NULL);
-                smtp_check("", 334);
-                encode_base64(NULL, G.pass, NULL);
+                if ((opts & OPT_am_mask) == OPT_am_plain) {
+                        char *plain_auth;
+                        size_t user_len, pass_len;
+                        user_len = strlen(G.user);
+                        pass_len = strlen(G.pass);
+                        smtp_check("AUTH PLAIN", 334);
+                        // use \1 as placeholders for \0 (format string is NUL-terminated)
+                        plain_auth = xasprintf("\1%s\1%s", G.user, G.pass);
+                        // substitute placeholders
+                        plain_auth[0] = '\0';
+                        plain_auth[1 + user_len] = '\0';
+                        encode_n_base64(NULL, plain_auth, 1 + user_len + 1 + pass_len, NULL);
+                        free(plain_auth);
+                } else if ((opts & OPT_am_mask) == OPT_am_login) {
+                        smtp_check("AUTH LOGIN", 334);
+                        encode_base64(NULL, G.user, NULL);
+                        smtp_check("", 334);
+                        encode_base64(NULL, G.pass, NULL);
+                }
                 smtp_check("", 235);
         }