modpost: fix broken sym->namespace for external module builds (389eb3f5) · Commits · 戴 / test

Currently, external module builds produce tons of false-positives: WARNING: module <mod> uses symbol <sym> from namespace <ns>, but does not import it. Here, the <ns> part shows a random string. When you build external modules, the symbol info of vmlinux and in-kernel modules are read from $(objtree)/Module.symvers, but read_dump() is buggy in multiple ways: [1] When the modpost is run for vmlinux and in-kernel modules, sym_extract_namespace() allocates memory for the namespace. On the other hand, read_dump() does not, then sym->namespace will point to somewhere in the line buffer of get_next_line(). The data in the buffer will be replaced soon, and sym->namespace will end up with pointing to unrelated data. As a result, check_exports() will show random strings in the warning messages. [2] When there is no namespace, sym_extract_namespace() returns NULL. On the other hand, read_dump() sets namespace to an empty string "". (but, it will be later replaced with unrelated data due to bug [1].) The check_exports() shows a warning unless exp->namespace is NULL, so every symbol read from read_dump() emits the warning, which is mostly false positive. To address [1], sym_add_exported() calls strdup() for s->namespace. The namespace from sym_extract_namespace() must be freed to avoid memory leak. For [2], I changed the if-conditional in check_exports(). This commit also fixes sym_add_exported() to set s->namespace correctly when the symbol is preloaded. Reviewed-by:

Matthias Maennich <maennich@google.com> Signed-off-by:

Masahiro Yamada <yamada.masahiro@socionext.com> Signed-off-by:

Jessica Yu <jeyu@kernel.org>

scripts/mod/modpost.c

+8 −5

Original line number	Diff line number	Diff line
		@@ -166,7 +166,7 @@ struct symbol {
		struct module *module;
		unsigned int crc;
		int crc_valid;
		const char *namespace;
		char *namespace;
		unsigned int weak:1;
		unsigned int vmlinux:1; /* 1 if symbol is defined in vmlinux */
		unsigned int kernel:1; /* 1 if symbol is from kernel
		@@ -348,7 +348,7 @@ static enum export export_from_sec(struct elf_info *elf, unsigned int sec)
		return export_unknown;
		}

		static const char sym_extract_namespace(const char *symname)
		static char sym_extract_namespace(const char *symname)
		{
		char *namespace = NULL;
		char *ns_separator;
		@@ -373,7 +373,6 @@ static struct symbol sym_add_exported(const char name, const char *namespace,

		if (!s) {
		s = new_symbol(name, mod, export);
		s->namespace = namespace;
		} else {
		if (!s->preloaded) {
		warn("%s: '%s' exported twice. Previous export was in %s%s\n",
		@@ -384,6 +383,8 @@ static struct symbol sym_add_exported(const char name, const char *namespace,
		s->module = mod;
		}
		}
		free(s->namespace);
		s->namespace = namespace ? strdup(namespace) : NULL;
		s->preloaded = 0;
		s->vmlinux = is_vmlinux(mod->name);
		s->kernel = 0;
		@@ -670,7 +671,8 @@ static void handle_modversions(struct module mod, struct elf_info info,
		unsigned int crc;
		enum export export;
		bool is_crc = false;
		const char name, namespace;
		const char *name;
		char *namespace;

		if ((!is_vmlinux(mod->name) \|\| mod->is_dot_o) &&
		strstarts(symname, "__ksymtab"))
		@@ -745,6 +747,7 @@ static void handle_modversions(struct module mod, struct elf_info info,
		name = symname + strlen("__ksymtab_");
		namespace = sym_extract_namespace(&name);
		sym_add_exported(name, namespace, mod, export);
		free(namespace);
		}
		if (strcmp(symname, "init_module") == 0)
		mod->has_init = 1;
		@@ -2193,7 +2196,7 @@ static int check_exports(struct module *mod)
		else
		basename = mod->name;

		if (exp->namespace) {
		if (exp->namespace && exp->namespace[0]) {
		add_namespace(&mod->required_namespaces,
		exp->namespace);

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