linux-kernel - Re: /proc/kallsyms race vs module unload

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Message-ID: <45F7E7D6.1000904@grupopie.com>
Date:	Wed, 14 Mar 2007 12:17:26 +0000
From:	Paulo Marques <pmarques@...popie.com>
To:	Alexey Dobriyan <adobriyan@...il.com>
CC:	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: /proc/kallsyms race vs module unload

Alexey Dobriyan wrote:
> On Tue, Mar 13, 2007 at 06:49:50PM +0000, Paulo Marques wrote:
>> Alexey Dobriyan wrote:
>>> [...]
>>> What happens is that module_get_kallsym() drops module_mutex,
>>> returns "struct module *", module unloaded, "struct module *"
>>> used.
>> The only use for the "struct module *" is to display the name of the
>> module.
> 
> Ehh?
> 
>> This can be solved by adding a "char mod_name[MODULE_NAME_LEN];" field
>> to "kallsym_iter" and copy the name of the module over, while still
>> holding module_mutex. It would be slightly slower, but safer.
> 
> 	iter->owner = module_get_kallsym(iter->pos - kallsyms_num_syms,
> 					 &iter->value, &iter->type,
> 					 iter->name, sizeof(iter->name));
> 	if (iter->owner == NULL)
> 		return 0;
> 
> 	/* Label it "global" if it is exported, "local" if not exported. */
> 	iter->type = is_exported(iter->name, iter->owner)
> 					     ^^^^^^^^^^^

Yes, there is this "is_exported" call, but his can be moved completely 
into "module_get_kallsym" and have the "type" returned be already upper 
/ lower case.

That, together with filling the module name "module_get_kallsym()" would 
make the returned "struct module *" unneeded.

Since kallsyms is the only caller of that function, we can change its 
interface to not return a "struct module *" at all, and return just an 
integer that means "symbol found" or "no more symbols".

I'm still volunteering to do that patch, but you seem more active than 
me at the moment...

-- 
Paulo Marques
Software Development Department - Grupo PIE, S.A.
Phone: +351 252 290600, Fax: +351 252 290601
Web: www.grupopie.com
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