linux-kernel - Re: [PATCH] modpost: abort if a module name is too long

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Date:   Mon, 29 May 2017 02:10:08 -0700
From:   Jessica Yu <jeyu@...hat.com>
To:     Xie XiuQi <xiexiuqi@...wei.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        rusty@...tcorp.com.au, john.wanghui@...wei.com,
        wencongyang2@...wei.com, guijianfeng@...wei.com,
        gaowanlong@...wei.com
Subject: Re: [PATCH] modpost: abort if a module name is too long

+++ Xie XiuQi [20/05/17 15:46 +0800]:
>From: Wanlong Gao <gaowanlong@...wei.com>
>
>Module name has a limited length, but currently the build system
>allows the build finishing even if the module name is too long.
>
>  CC      /root/kprobe_example/abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz.mod.o
>/root/kprobe_example/abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz.mod.c:9:2:
>warning: initializer-string for array of chars is too long [enabled by default]
>  .name = KBUILD_MODNAME,
>  ^
>
>but it's merely a warning.
>
>This patch adds the check of the module name length in modpost and stops
>the build properly.
>
>Signed-off-by: Wanlong Gao <gaowanlong@...wei.com>
>Signed-off-by: Xie XiuQi <xiexiuqi@...wei.com>
>---
> scripts/mod/modpost.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
>diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
>index 30d752a..db11c57 100644
>--- a/scripts/mod/modpost.c
>+++ b/scripts/mod/modpost.c
>@@ -2166,6 +2166,17 @@ static int add_versions(struct buffer *b, struct module *mod)
> {
> 	struct symbol *s, *exp;
> 	int err = 0;
>+	const char *mod_name;
>+
>+	mod_name = strrchr(mod->name, '/');
>+	if (mod_name == NULL)
>+		mod_name = mod->name;
>+	else
>+		mod_name++;
>+	if (strlen(mod_name) >= MODULE_NAME_LEN) {
>+		merror("module name is too long [%s.ko]\n", mod->name);
>+		return 1;
>+	}

Hi Xie,

This check shouldn't be in add_versions() (which does something else entirely),
it should probably be put in a separate helper function called from main. But
I'm not a big fan of the extra string manipulation to do something this simple.

I think this check can be vastly simplified, how about something like the
following?

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 48397fe..bb09fc7 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -2139,6 +2139,9 @@ static void add_header(struct buffer *b, struct module *mod)
 			      "#endif\n");
 	buf_printf(b, "\t.arch = MODULE_ARCH_INIT,\n");
 	buf_printf(b, "};\n");
+	buf_printf(b, "\n");
+	buf_printf(b, "static void __attribute__((section(\".discard\"), used)) __modname_test(void)\n");
+	buf_printf(b, "{ BUILD_BUG_ON(sizeof(KBUILD_MODNAME) > MODULE_NAME_LEN); }\n");
 }
 
 static void add_intree_flag(struct buffer *b, int is_intree)

This simply checks if KBUILD_MODNAME > MODULE_NAME_LEN and breaks the build if
it does.

Jessica

> 	for (s = mod->unres; s; s = s->next) {
> 		exp = find_symbol(s->name);
>-- 
>1.8.3.1
>