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

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Date:   Tue, 30 May 2017 20:30:44 -0700
From:   Jessica Yu <jeyu@...hat.com>
To:     Wanlong Gao <gaowanlong@...wei.com>
Cc:     Xie XiuQi <xiexiuqi@...wei.com>, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, rusty@...tcorp.com.au,
        john.wanghui@...wei.com, wencongyang2@...wei.com,
        guijianfeng@...wei.com
Subject: Re: [PATCH] modpost: abort if a module name is too long

+++ Wanlong Gao [31/05/17 10:23 +0800]:
>Hi Jessica,
>
>On 2017/5/29 17:10, Jessica Yu wrote:
>> +++ 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?
>
>This looks better, would you apply your following patch?
>
>Reviewed-by: Wanlong Gao <gaowanlong@...wei.com>
>Tested-by: Wanlong Gao <gaowanlong@...wei.com>

Sure, thanks for testing. I'll go ahead and format this into a proper
patch and resend.

Jessica

>>
>> 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
>>>
>>
>> .
>>
>