Move the cli buffer to VSB (from stack)

If the cli buffer is allocated on the stack, the mgt process will
crash hard for big values of this parameter. Instead we allocate on
the heap.

The new cli buffer an "auto" VSB. This means that the varnish
parameter cli_buffer is ignored from now on, and the manual marks it
as deprecated.

Closes: #2382

bin/varnishd/mgt/mgt_cli.c

@@ -67,6 +67,8 @@ static int		cli_i = -1, cli_o = -1;
 struct VCLS		*mgt_cls;
 static const char	*secret_file;
 
+struct vsb		*cli_buf = NULL;
+
 /*--------------------------------------------------------------------*/
 
 static void __match_proto__(cli_func_t)
@@ -177,24 +179,30 @@ mgt_cli_askchild(unsigned *status, char **resp, const char *fmt, ...)
 	int i, j;
 	va_list ap;
 	unsigned u;
-	char buf[mgt_param.cli_buffer], *p;
+
+	if (cli_buf == NULL) {
+		cli_buf = VSB_new_auto();
+		AN(cli_buf);
+	} else {
+		VSB_clear(cli_buf);
+	}
 
 	if (resp != NULL)
 		*resp = NULL;
 	if (status != NULL)
 		*status = 0;
-	if (cli_i < 0|| cli_o < 0) {
+	if (cli_i < 0 || cli_o < 0) {
 		if (status != NULL)
 			*status = CLIS_CANT;
 		return (CLIS_CANT);
 	}
 	va_start(ap, fmt);
-	vbprintf(buf, fmt, ap);
+	AZ(VSB_vprintf(cli_buf, fmt, ap));
 	va_end(ap);
-	p = strchr(buf, '\0');
-	assert(p != NULL && p > buf && p[-1] == '\n');
-	i = p - buf;
-	j = write(cli_o, buf, i);
+	AZ(VSB_finish(cli_buf));
+	i = VSB_len(cli_buf);
+	assert(i > 0 && VSB_data(cli_buf)[i - 1] == '\n');
+	j = write(cli_o, VSB_data(cli_buf), i);
 	if (j != i) {
 		if (status != NULL)
 			*status = CLIS_COMMS;

bin/varnishtest/tests/r02382.vtc

+varnishtest "Very very big cli_buffer"
+
+# If the cli_buffer is on the stack, setting it very big can crash varnish
+
+server s1 {
+       rxreq
+       expect req.url == "/1"
+       txresp
+} -start
+
+varnish v1 -arg "-p cli_buffer=32M" -vcl+backend {
+} -start
+
+varnish v1 -cliok "ping"
+
+delay .5
+
+client c1 {
+       txreq -url /1
+       rxresp
+} -run

include/tbl/params.h

@@ -294,10 +294,8 @@ PARAM(
 	/* units */	"bytes",
 	/* flags */	0,
 	/* s-text */
-	"Size of buffer for CLI command input.\n"
-	"You may need to increase this if you have big VCL files and use "
-	"the vcl.inline CLI command.\n"
-	"NB: Must be specified with -p to have effect.",
+	"DEPRECATED: This parameter is ignored.\n"
+	"Memory for the CLI command buffer is now dynamically allocated.",
 	/* l-text */	"",
 	/* func */	NULL
 )