libkmod: add mask command

Mask command prevents modules from loading. It intends to be a strict
and intent-based replacement for variations of install and blacklist
commands, for example:

* install module /bin/false
* install module /bin/true
* blacklist module, with modprobe -b

This commit is a pure extension and the already established behaviour
is not expected to change as a result.

Co-authored-by: Jakub Ślepecki <[email protected]>
Signed-off-by: Jakub Ślepecki <[email protected]>
Signed-off-by: Dawid Osuchowski <[email protected]>

Author: whythefyouflying

libkmod/docs/libkmod-docs.xml

@@ -60,4 +60,8 @@
     <title>Index of new symbols in 33</title>
     <xi:include href="xml/api-index-33.xml"></xi:include>
   </chapter>
+  <chapter id="api-index-v35" role="35">
+    <title>Index of new symbols in 35</title>
+    <xi:include href="xml/api-index-35.xml"></xi:include>
+  </chapter>
 </book>

libkmod/docs/libkmod-sections.txt

@@ -35,6 +35,7 @@ kmod_list_prev
 kmod_config_iter
 kmod_config_get_blacklists
 kmod_config_get_install_commands
+kmod_config_get_masks
 kmod_config_get_remove_commands
 kmod_config_get_aliases
 kmod_config_get_options

libkmod/libkmod-config.c

@@ -50,6 +50,11 @@ struct kmod_weakdep {
 	unsigned int n_weak;
 };
 
+const char *kmod_mask_get_modname(const struct kmod_list *l)
+{
+	return l->data;
+}
+
 const char *kmod_blacklist_get_modname(const struct kmod_list *l)
 {
 	return l->data;
@@ -231,6 +236,27 @@ static int kmod_config_add_blacklist(struct kmod_config *config, const char *mod
 	return 0;
 }
 
+static int kmod_config_add_mask(struct kmod_config *config, const char *modname)
+{
+	_cleanup_free_ char *p;
+	struct kmod_list *list;
+
+	DBG(config->ctx, "modname=%s\n", modname);
+
+	_clang_suppress_alloc_ p = strdup(modname);
+	if (!p)
+		return -ENOMEM;
+
+	list = kmod_list_append(config->masks, p);
+	if (!list)
+		return -ENOMEM;
+
+	TAKE_PTR(p);
+	config->masks = list;
+
+	return 0;
+}
+
 static int kmod_config_add_softdep(struct kmod_config *config, const char *modname,
 				   const char *line)
 {
@@ -612,18 +638,24 @@ static char *weakdep_to_char(struct kmod_weakdep *dep)
 static void kcmdline_parse_result(struct kmod_config *config, char *modname, char *param,
 				  char *value)
 {
+	bool is_blacklist, is_mask;
 	if (modname == NULL || param == NULL)
 		return;
 
 	DBG(config->ctx, "%s %s\n", modname, param);
 
-	if (streq(modname, "modprobe") && !strncmp(param, "blacklist=", 10)) {
+	is_blacklist = !strncmp(param, "blacklist=", 10);
+	is_mask = !strncmp(param, "mask=", 5);
+	if (streq(modname, "modprobe") && (is_blacklist || is_mask)) {
 		for (;;) {
 			char *t = strsep(&value, ",");
 			if (t == NULL)
 				break;
 
-			kmod_config_add_blacklist(config, t);
+			if (is_blacklist)
+				kmod_config_add_blacklist(config, t);
+			else
+				kmod_config_add_mask(config, t);
 		}
 	} else {
 		if (underscores(modname) < 0) {
@@ -829,6 +861,13 @@ static int kmod_config_parse(struct kmod_config *config, int fd, const char *fil
 
 			kmod_config_add_command(config, modname, installcmd, cmd,
 						&config->install_commands);
+		} else if (streq(cmd, "mask")) {
+			char *modname = strtok_r(NULL, "\t ", &saveptr);
+
+			if (underscores(modname) < 0)
+				goto syntax_error;
+
+			kmod_config_add_mask(config, modname);
 		} else if (streq(cmd, "remove")) {
 			char *modname = strtok_r(NULL, "\t ", &saveptr);
 			char *removecmd = strtok_r(NULL, "\0", &saveptr);
@@ -878,6 +917,7 @@ void kmod_config_free(struct kmod_config *config)
 	kmod_list_release(config->blacklists, free);
 	kmod_list_release(config->options, free);
 	kmod_list_release(config->install_commands, free);
+	kmod_list_release(config->masks, free);
 	kmod_list_release(config->remove_commands, free);
 	kmod_list_release(config->softdeps, free);
 	kmod_list_release(config->weakdeps, free);
@@ -1100,6 +1140,7 @@ int kmod_config_new(struct kmod_ctx *ctx, struct kmod_config **p_config,
 enum config_type {
 	CONFIG_TYPE_BLACKLIST = 0,
 	CONFIG_TYPE_INSTALL,
+	CONFIG_TYPE_MASK,
 	CONFIG_TYPE_REMOVE,
 	CONFIG_TYPE_ALIAS,
 	CONFIG_TYPE_OPTION,
@@ -1150,6 +1191,10 @@ static struct kmod_config_iter *kmod_config_iter_new(const struct kmod_ctx *ctx,
 		iter->get_key = kmod_command_get_modname;
 		iter->get_value = kmod_command_get_command;
 		break;
+	case CONFIG_TYPE_MASK:
+		iter->list = config->masks;
+		iter->get_key = kmod_mask_get_modname;
+		break;
 	case CONFIG_TYPE_REMOVE:
 		iter->list = config->remove_commands;
 		iter->get_key = kmod_command_get_modname;
@@ -1200,6 +1245,14 @@ KMOD_EXPORT struct kmod_config_iter *kmod_config_get_install_commands(const stru
 	return kmod_config_iter_new(ctx, CONFIG_TYPE_INSTALL);
 }
 
+KMOD_EXPORT struct kmod_config_iter *kmod_config_get_masks(const struct kmod_ctx *ctx)
+{
+	if (ctx == NULL)
+		return NULL;
+
+	return kmod_config_iter_new(ctx, CONFIG_TYPE_MASK);
+}
+
 // clang-format off
 KMOD_EXPORT struct kmod_config_iter *kmod_config_get_remove_commands(const struct kmod_ctx *ctx)
 // clang-format on

libkmod/libkmod-internal.h

@@ -99,6 +99,7 @@ struct kmod_config {
 	struct kmod_list *aliases;
 	struct kmod_list *blacklists;
 	struct kmod_list *options;
+	struct kmod_list *masks;
 	struct kmod_list *remove_commands;
 	struct kmod_list *install_commands;
 	struct kmod_list *softdeps;
@@ -112,6 +113,7 @@ _nonnull_all_ void kmod_config_free(struct kmod_config *config);
 _nonnull_all_ const char *kmod_blacklist_get_modname(const struct kmod_list *l);
 _nonnull_all_ const char *kmod_alias_get_name(const struct kmod_list *l);
 _nonnull_all_ const char *kmod_alias_get_modname(const struct kmod_list *l);
+_nonnull_all_ const char *kmod_mask_get_modname(const struct kmod_list *l);
 _nonnull_all_ const char *kmod_option_get_options(const struct kmod_list *l);
 _nonnull_all_ const char *kmod_option_get_modname(const struct kmod_list *l);
 _nonnull_all_ const char *kmod_command_get_command(const struct kmod_list *l);

libkmod/libkmod-module.c

@@ -735,12 +735,30 @@ static bool module_is_blacklisted(const struct kmod_module *mod)
 	return false;
 }
 
+static bool module_is_masked(const struct kmod_module *mod)
+{
+	const struct kmod_ctx *ctx = mod->ctx;
+	const struct kmod_config *config = kmod_get_config(ctx);
+	const struct kmod_list *bl = config->masks;
+	const struct kmod_list *l;
+
+	kmod_list_foreach(l, bl) {
+		const char *modname = kmod_mask_get_modname(l);
+
+		if (streq(modname, mod->name))
+			return true;
+	}
+
+	return false;
+}
+
 KMOD_EXPORT int kmod_module_apply_filter(const struct kmod_ctx *ctx,
 					 enum kmod_filter filter_type,
 					 const struct kmod_list *input,
 					 struct kmod_list **output)
 {
 	const struct kmod_list *li;
+	int err = 0;
 
 	if (ctx == NULL || output == NULL)
 		return -ENOENT;
@@ -759,9 +777,21 @@ KMOD_EXPORT int kmod_module_apply_filter(const struct kmod_ctx *ctx,
 		if ((filter_type & KMOD_FILTER_BUILTIN) && kmod_module_is_builtin(mod))
 			continue;
 
+		if ((filter_type & KMOD_FILTER_MASK) && module_is_masked(mod)) {
+			if (mod->required) {
+				ERR(mod->ctx, "module is masked: %s\n",
+				    kmod_module_get_name(mod));
+				err = -EINVAL;
+				goto fail;
+			} else
+				continue;
+		}
+
 		node = kmod_list_append(*output, mod);
-		if (node == NULL)
+		if (node == NULL) {
+			err = -ENOMEM;
 			goto fail;
+		}
 
 		*output = node;
 		kmod_module_ref(mod);
@@ -772,7 +802,7 @@ KMOD_EXPORT int kmod_module_apply_filter(const struct kmod_ctx *ctx,
 fail:
 	kmod_module_unref_list(*output);
 	*output = NULL;
-	return -ENOMEM;
+	return err;
 }
 
 static int command_do(struct kmod_module *mod, const char *type, const char *cmd)
@@ -1006,7 +1036,7 @@ KMOD_EXPORT int kmod_module_probe_insert_module(
 	const void *data,
 	void (*print_action)(struct kmod_module *m, bool install, const char *options))
 {
-	struct kmod_list *list = NULL, *l;
+	struct kmod_list *list = NULL, *l, *filtered = NULL;
 	struct probe_insert_cb cb;
 	int err;
 
@@ -1020,6 +1050,11 @@ KMOD_EXPORT int kmod_module_probe_insert_module(
 			return 0;
 	}
 
+	if (module_is_masked(mod)) {
+		ERR(mod->ctx, "module is masked: %s\n", kmod_module_get_name(mod));
+		return -EINVAL;
+	}
+
 	if (module_is_blacklisted(mod)) {
 		if (mod->alias != NULL && (flags & KMOD_PROBE_APPLY_BLACKLIST_ALIAS_ONLY))
 			return KMOD_PROBE_APPLY_BLACKLIST_ALIAS_ONLY;
@@ -1036,15 +1071,23 @@ KMOD_EXPORT int kmod_module_probe_insert_module(
 	if (err < 0)
 		return err;
 
-	if (flags & KMOD_PROBE_APPLY_BLACKLIST_ALL) {
-		struct kmod_list *filtered = NULL;
+	err = kmod_module_apply_filter(mod->ctx, KMOD_FILTER_MASK, list, &filtered);
+	kmod_module_unref_list(list);
+	if (err < 0)
+		return err;
+
+	if (filtered == NULL)
+		return -EINVAL;
 
+	list = filtered;
+
+	if (flags & KMOD_PROBE_APPLY_BLACKLIST_ALL) {
 		err = kmod_module_apply_filter(mod->ctx, KMOD_FILTER_BLACKLIST, list,
 					       &filtered);
+		kmod_module_unref_list(list);
 		if (err < 0)
 			return err;
 
-		kmod_module_unref_list(list);
 		if (filtered == NULL)
 			return KMOD_PROBE_APPLY_BLACKLIST_ALL;
 

libkmod/libkmod.h

@@ -365,6 +365,22 @@ struct kmod_list *kmod_list_prev(const struct kmod_list *list,
  */
 struct kmod_config_iter;
 
+/**
+ * kmod_config_get_masks:
+ * @ctx: kmod library context
+ *
+ * Retrieve an iterator to deal with the mask list maintained inside the
+ * library. See kmod_config_iter_get_key(), kmod_config_iter_get_value() and
+ * kmod_config_iter_next(). At least one call to kmod_config_iter_next() must
+ * be made to initialize the iterator and check if it's valid.
+ *
+ * Returns: a new iterator over the masks or NULL on failure. Free it
+ * with kmod_config_iter_free_iter().
+ *
+ * Since: 35
+ */
+struct kmod_config_iter *kmod_config_get_masks(const struct kmod_ctx *ctx);
+
 /**
  * kmod_config_get_blacklists:
  * @ctx: kmod library context
@@ -905,12 +921,14 @@ int kmod_module_get_weakdeps(const struct kmod_module *mod, struct kmod_list **w
  * kmod_filter:
  * @KMOD_FILTER_BLACKLIST: filter modules in blacklist out
  * @KMOD_FILTER_BUILTIN: filter builtin modules out
+ * @KMOD_FILTER_MASK: filter masked modules out
  *
  * Bitmask defining what gets filtered out, used by kmod_module_apply_filter().
  */
 enum kmod_filter {
 	KMOD_FILTER_BLACKLIST = 0x00001,
 	KMOD_FILTER_BUILTIN = 0x00002,
+	KMOD_FILTER_MASK = 0x00004,
 };
 
 /**

libkmod/libkmod.sym

@@ -105,3 +105,8 @@ global:
 	kmod_config_get_weakdeps;
 	kmod_module_get_weakdeps;
 } LIBKMOD_30;
+
+LIBKMOD_35 {
+global:
+	kmod_config_get_masks;
+} LIBKMOD_33;

man/modprobe.8.scd

@@ -23,7 +23,8 @@ that for convenience, there is no difference between \_ and - in module names
 directory @DISTCONFDIR@/`uname -r` for all the modules and other files, except
 for the optional configuration files (see *modprobe.d*(5)). *modprobe* will also
 use module options specified on the kernel command line in the form of
-<module>.<option> and blacklists in the form of modprobe.blacklist=<module>.
+<module>.<option>, blacklists in the form of modprobe.blacklist=<module>
+and masks in modprobe.mask=<module>.
 
 Note that unlike in 2.4 series Linux kernels (which are not supported by this
 tool) this version of *modprobe* does not do anything to the module itself: the

man/modprobe.d.5.scd

@@ -108,6 +108,10 @@ install _modulename_ _command..._
 	/sbin/modprobe barney; /sbin/modprobe --ignore-install fred
 	$CMDLINE_OPTS"
 
+mask _modulename_
+	This command prevents _modulename_ from being loaded directly
+	or through any of its aliases.
+
 options _modulename_ _option..._
 	This command allows you to add options to the module _modulename_ (which
 	might be an alias) every time it is inserted into the kernel: whether

scripts/setup-rootfs.sh

@@ -105,6 +105,12 @@ map=(
     ["test-modprobe/blacklist-loaded$MODULE_DIRECTORY/4.4.4/kernel/"]="mod-simple.ko"
     ["test-modprobe/blacklist-softdep$MODULE_DIRECTORY/4.4.4/kernel/mod-foo-a.ko"]="mod-foo-a.ko"
     ["test-modprobe/blacklist-softdep$MODULE_DIRECTORY/4.4.4/kernel/mod-simple.ko"]="mod-simple.ko"
+    ["test-modprobe/mask$MODULE_DIRECTORY/4.4.4/kernel/mod-foo-a.ko"]="mod-foo-a.ko"
+    ["test-modprobe/mask$MODULE_DIRECTORY/4.4.4/kernel/mod-foo-b.ko"]="mod-foo-b.ko"
+    ["test-modprobe/mask$MODULE_DIRECTORY/4.4.4/kernel/mod-foo-c.ko"]="mod-foo-c.ko"
+    ["test-modprobe/mask$MODULE_DIRECTORY/4.4.4/kernel/mod-foo.ko"]="mod-foo.ko"
+    ["test-modprobe/mask-softdep$MODULE_DIRECTORY/4.4.4/kernel/mod-foo-a.ko"]="mod-foo-a.ko"
+    ["test-modprobe/mask-softdep$MODULE_DIRECTORY/4.4.4/kernel/mod-simple.ko"]="mod-simple.ko"
     ["test-depmod/modules-order-compressed$MODULE_DIRECTORY/4.4.4/kernel/drivers/block/cciss.ko"]="mod-fake-cciss.ko"
     ["test-depmod/modules-order-compressed$MODULE_DIRECTORY/4.4.4/kernel/drivers/scsi/hpsa.ko"]="mod-fake-hpsa.ko"
     ["test-depmod/modules-order-compressed$MODULE_DIRECTORY/4.4.4/kernel/drivers/scsi/scsi_mod.ko"]="mod-fake-scsi-mod.ko"