linux-kernel - [PATCH 1/7] modpost: fix broken sym->namespace for external module builds

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Date:   Fri, 27 Sep 2019 18:35:57 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     Matthias Maennich <maennich@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Martijn Coenen <maco@...roid.com>,
        Will Deacon <will.deacon@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/7] 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() correctly 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], I added NOFAIL(strdup(...)) to allocate memory.
For [2], I changed the if-conditional in check_exports().

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

 scripts/mod/modpost.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 3961941e8e7a..5c628a7d80f7 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -2195,7 +2195,7 @@ 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);

@@ -2453,7 +2453,7 @@ static void read_dump(const char *fname, unsigned int kernel)
 			mod = new_module(modname);
 			mod->skip = 1;
 		}
-		s = sym_add_exported(symname, namespace, mod,
+		s = sym_add_exported(symname, NOFAIL(strdup(namespace)), mod,
 				     export_no(export));
 		s->kernel    = kernel;
 		s->preloaded = 1;
-- 
2.17.1