enable embedding arbitrarily long strings into IMAP commands

the AUTHENTICATE command may get insanely long for GSSAPI when SASL-IR
is available. instead of growing the buffers each time someone hits the
limit (as done in f7cec306), remove the limitation altogether.

imap_vprintf() still contains a fixed-size buffer which could overflow
when really long strings (e.g., mailbox names) need to be quoted. this
seems very unlikely, so we'll deal with it if someone actually hits it.

REFMAIL: 87sg1qxdye.fsf@cern.ch

src/drv_imap.c

@@ -335,42 +335,45 @@ done_imap_cmd( imap_store_t *ctx, imap_cmd_t *cmd, int response )
 static void
 send_imap_cmd( imap_store_t *ctx, imap_cmd_t *cmd )
 {
-	int litplus, iovcnt = 1;
+	int litplus, iovcnt = 3;
-	int bufl;
+	uint tbufl, lbufl;
-	const char *buffmt;
+	conn_iovec_t iov[5];
-	conn_iovec_t iov[3];
+	char tagbuf[16];
-	char buf[4096];
+	char lenbuf[16];
 
 	cmd->tag = ++ctx->nexttag;
+	tbufl = nfsnprintf( tagbuf, sizeof(tagbuf), "%d ", cmd->tag );
 	if (!cmd->param.data) {
-		buffmt = "%d %s\r\n";
+		memcpy( lenbuf, "\r\n", 3 );
+		lbufl = 2;
 		litplus = 0;
 	} else if ((cmd->param.to_trash && ctx->trashnc == TrashUnknown) || !CAP(LITERALPLUS) || cmd->param.data_len >= 100*1024) {
-		buffmt = "%d %s{%d}\r\n";
+		lbufl = nfsnprintf( lenbuf, sizeof(lenbuf), "{%u}\r\n", cmd->param.data_len );
 		litplus = 0;
 	} else {
-		buffmt = "%d %s{%d+}\r\n";
+		lbufl = nfsnprintf( lenbuf, sizeof(lenbuf), "{%u+}\r\n", cmd->param.data_len );
 		litplus = 1;
 	}
-DIAG_PUSH
-DIAG_DISABLE("-Wformat-nonliteral")
-	bufl = nfsnprintf( buf, sizeof(buf), buffmt,
-	                   cmd->tag, cmd->cmd, cmd->param.data_len );
-DIAG_POP
 	if (DFlags & DEBUG_NET) {
 		if (ctx->num_in_progress)
 			printf( "(%d in progress) ", ctx->num_in_progress );
 		if (starts_with( cmd->cmd, -1, "LOGIN", 5 ))
-			printf( "%s>>> %d LOGIN <user> <pass>\n", ctx->label, cmd->tag );
+			printf( "%s>>> %sLOGIN <user> <pass>\r\n", ctx->label, tagbuf );
 		else if (starts_with( cmd->cmd, -1, "AUTHENTICATE PLAIN", 18 ))
-			printf( "%s>>> %d AUTHENTICATE PLAIN <authdata>\n", ctx->label, cmd->tag );
+			printf( "%s>>> %sAUTHENTICATE PLAIN <authdata>\r\n", ctx->label, tagbuf );
 		else
-			printf( "%s>>> %s", ctx->label, buf );
+			printf( "%s>>> %s%s%s", ctx->label, tagbuf, cmd->cmd, lenbuf );
 		fflush( stdout );
 	}
-	iov[0].buf = buf;
+	iov[0].buf = tagbuf;
-	iov[0].len = (uint)bufl;
+	iov[0].len = tbufl;
 	iov[0].takeOwn = KeepOwn;
+	iov[1].buf = cmd->cmd;
+	iov[1].len = strlen( cmd->cmd );
+	iov[1].takeOwn = KeepOwn;
+	iov[2].buf = lenbuf;
+	iov[2].len = lbufl;
+	iov[2].takeOwn = KeepOwn;
 	if (litplus) {
 		if (DFlags & DEBUG_NET_ALL) {
 			printf( "%s>>>>>>>>>\n", ctx->label );
@@ -378,15 +381,15 @@ DIAG_POP
 			printf( "%s>>>>>>>>>\n", ctx->label );
 			fflush( stdout );
 		}
-		iov[1].buf = cmd->param.data;
+		iov[3].buf = cmd->param.data;
-		iov[1].len = cmd->param.data_len;
+		iov[3].len = cmd->param.data_len;
-		iov[1].takeOwn = GiveOwn;
+		iov[3].takeOwn = GiveOwn;
 		cmd->param.data = NULL;
 		ctx->buffer_mem -= cmd->param.data_len;
-		iov[2].buf = "\r\n";
+		iov[4].buf = "\r\n";
-		iov[2].len = 2;
+		iov[4].len = 2;
-		iov[2].takeOwn = KeepOwn;
+		iov[4].takeOwn = KeepOwn;
-		iovcnt = 3;
+		iovcnt = 5;
 	}
 	socket_write( &ctx->conn, iov, iovcnt );
 	if (cmd->param.to_trash && ctx->trashnc == TrashUnknown)
@@ -512,7 +515,20 @@ imap_vprintf( const char *fmt, va_list ap )
 	const char *s;
 	char *d, *ed;
 	char c;
-	char buf[4096];
+#define MAX_SEGS 16
+#define add_seg(s, l) \
+		do { \
+			if (nsegs == MAX_SEGS) \
+				oob(); \
+			segs[nsegs] = s; \
+			segls[nsegs++] = l; \
+			totlen += l; \
+		} while (0)
+	int nsegs = 0;
+	uint totlen = 0;
+	const char *segs[MAX_SEGS];
+	uint segls[MAX_SEGS];
+	char buf[1000];
 
 	d = buf;
 	ed = d + sizeof(buf);
@@ -521,12 +537,10 @@ imap_vprintf( const char *fmt, va_list ap )
 		c = *fmt;
 		if (!c || c == '%') {
 			uint l = fmt - s;
-			if (d + l > ed)
+			if (l)
-				oob();
+				add_seg( s, l );
-			memcpy( d, s, l );
-			d += l;
 			if (!c)
-				return nfstrndup( buf, (size_t)(d - buf) );
+				break;
 			uint maxlen = UINT_MAX;
 			c = *++fmt;
 			if (c == '\\') {
@@ -535,6 +549,7 @@ imap_vprintf( const char *fmt, va_list ap )
 					fputs( "Fatal: unsupported escaped format specifier. Please report a bug.\n", stderr );
 					abort();
 				}
+				char *bd = d;
 				s = va_arg( ap, const char * );
 				while ((c = *s++)) {
 					if (d + 2 > ed)
@@ -543,6 +558,9 @@ imap_vprintf( const char *fmt, va_list ap )
 						*d++ = '\\';
 					*d++ = c;
 				}
+				l = d - bd;
+				if (l)
+					add_seg( bd, l );
 			} else { /* \\ cannot be combined with anything else. */
 				if (c == '.') {
 					c = *++fmt;
@@ -556,18 +574,21 @@ imap_vprintf( const char *fmt, va_list ap )
 				if (c == 'c') {
 					if (d + 1 > ed)
 						oob();
+					add_seg( d, 1 );
 					*d++ = (char)va_arg( ap , int );
 				} else if (c == 's') {
 					s = va_arg( ap, const char * );
 					l = strnlen( s, maxlen );
-					if (d + l > ed)
+					if (l)
-						oob();
+						add_seg( s, l );
-					memcpy( d, s, l );
-					d += l;
 				} else if (c == 'd') {
-					d += nfsnprintf( d, ed - d, "%d", va_arg( ap , int ) );
+					l = nfsnprintf( d, ed - d, "%d", va_arg( ap, int ) );
+					add_seg( d, l );
+					d += l;
 				} else if (c == 'u') {
-					d += nfsnprintf( d, ed - d, "%u", va_arg( ap , uint ) );
+					l = nfsnprintf( d, ed - d, "%u", va_arg( ap, uint ) );
+					add_seg( d, l );
+					d += l;
 				} else {
 					fputs( "Fatal: unsupported format specifier. Please report a bug.\n", stderr );
 					abort();
@@ -578,6 +599,13 @@ imap_vprintf( const char *fmt, va_list ap )
 			fmt++;
 		}
 	}
+	char *out = d = nfmalloc( totlen + 1 );
+	for (int i = 0; i < nsegs; i++) {
+		memcpy( d, segs[i], segls[i] );
+		d += segls[i];
+	}
+	*d = 0;
+	return out;
 }
 
 static void