discover/grub: Improve BLS grub environment variables expansion

The fields from a BootLoaderSpec file can contain environment variables,
in GRUB 2 these are show verbatim and are evaluated later when an entry
is selected. But on Petitboot these have to be expanded before creating
the GRUB 2 resources and show in the UI the values after the evaluation.

The current blscfg handler had a very limited support for variables, it
only had support for the options field and also didn't take into account
that variables could be mixed with literal values.

So for example the following fields were not expanded correctly:

  linux   $bootprefix/vmlinuz

  options $kernelopts foo=bar

  options foo=bar $kernelopts

  options $kernelopts $debugopts

Also change some of the tests to cover mixing variables and literals.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>

1 files changed, 69 insertions, 16 deletions

diff --git a/discover/grub2/blscfg.c b/discover/grub2/blscfg.c
index a381306..d4754aa 100644
--- a/discover/grub2/blscfg.c
+++ b/discover/grub2/blscfg.c
@@ -2,6 +2,7 @@
 #define _GNU_SOURCE
 
 #include <assert.h>
+#include <ctype.h>
 #include <stdlib.h>
 #include <string.h>
 #include <dirent.h>
@@ -34,54 +35,106 @@ struct bls_state {
 	const char *dtb;
 };
 
+static char *field_append(struct bls_state *state, int type, char *buffer,
+			  char *start, char *end)
+{
+	char *temp = talloc_strndup(state, start, end - start + 1);
+	const char *field = temp;
+
+	if (type == GRUB2_WORD_VAR) {
+		field = script_env_get(state->script, temp);
+		if (!field)
+			return buffer;
+	}
+
+	if (!buffer)
+		buffer = talloc_strdup(state->opt, field);
+	else
+		buffer = talloc_asprintf_append(buffer, "%s", field);
+
+	return buffer;
+}
+
+static char *expand_field(struct bls_state *state, char *value)
+{
+	char *buffer = NULL;
+	char *start = value;
+	char *end = value;
+	int type = GRUB2_WORD_TEXT;
+
+	while (*value) {
+		if (*value == '$') {
+			if (start != end) {
+				buffer = field_append(state, type, buffer,
+						      start, end);
+				if (!buffer)
+					return NULL;
+			}
+
+			type = GRUB2_WORD_VAR;
+			start = value + 1;
+		} else if (type == GRUB2_WORD_VAR) {
+			if (!isalnum(*value) && *value != '_') {
+				buffer = field_append(state, type, buffer,
+						      start, end);
+				type = GRUB2_WORD_TEXT;
+				start = value;
+			}
+		}
+
+		end = value;
+		value++;
+	}
+
+	if (start != end) {
+		buffer = field_append(state, type, buffer,
+				      start, end);
+		if (!buffer)
+			return NULL;
+	}
+
+	return buffer;
+}
+
 static void bls_process_pair(struct conf_context *conf, const char *name,
 			     char *value)
 {
 	struct bls_state *state = conf->parser_info;
 	struct discover_boot_option *opt = state->opt;
 	struct boot_option *option = opt->option;
-	const char *boot_args;
 
 	if (streq(name, "title")) {
-		state->title = talloc_strdup(state, value);
+		state->title = expand_field(state, value);
 		return;
 	}
 
 	if (streq(name, "version")) {
-		state->version = talloc_strdup(state, value);
+		state->version = expand_field(state, value);
 		return;
 	}
 
 	if (streq(name, "machine-id")) {
-		state->machine_id = talloc_strdup(state, value);
+		state->machine_id = expand_field(state, value);
 		return;
 	}
 
 	if (streq(name, "linux")) {
-		state->image = talloc_strdup(state, value);
+		state->image = expand_field(state, value);
 		return;
 	}
 
 	if (streq(name, "initrd")) {
-		state->initrd = talloc_strdup(state, value);
+		state->initrd = expand_field(state, value);
 		return;
 	}
 
 	if (streq(name, "devicetree")) {
-		state->dtb = talloc_strdup(state, value);
+		state->dtb = expand_field(state, value);
 		return;
 	}
 
 	if (streq(name, "options")) {
-		if (value[0] == '$') {
-			boot_args = script_env_get(state->script, value + 1);
-			if (!boot_args)
-				return;
-
-			option->boot_args = talloc_strdup(opt, boot_args);
-		} else {
-			option->boot_args = talloc_strdup(opt, value);
-		}
+		option->boot_args = expand_field(state, value);
 		return;
 	}
 }