modpost: fix broken sym->namespace for external module builds

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>

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index c4b536a..4d2cdb4 100644 (file)
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -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);