linux-kernel - Re: [PATCH 00/23] Removal of binary sysctl support

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Date:	Thu, 19 Nov 2009 14:22:53 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, john.johansen@...onical.com
Subject: Re: [PATCH 00/23] Removal of binary sysctl support

Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> writes:

> Hello.
>
> Eric W. Biederman wrote:
>> > Indeed. TOMOYO and AppArmor need a hint for prepending "/proc" prefix.
>> > A simple implementation which adds one bit to task_struct is shown below.
>> > In this way, not only the file permission checks inside dentry_open()
>> > but also the directory permission checks inside vfs_path_lookup() can be
>> > prepended "/proc" prefix. AppArmor might want to prepend "/proc" inside
>> > vfs_path_lookup().
>> 
>> There don't appear to be any security hooks in vfs_path_lookup().
>>
> OK. Then, AppArmor won't be confused.
>
>> Instead of current->in_sysctl we can just look at the path and see if
>> it is the root of the mount chain and if the fs is proc.
>> 
>> Something like:
>> 
>> diff --git a/security/tomoyo/realpath.c b/security/tomoyo/realpath.c
>> index 5f2e332..0b55faa 100644
>> --- a/security/tomoyo/realpath.c
>> +++ b/security/tomoyo/realpath.c
>> @@ -108,6 +108,15 @@ int tomoyo_realpath_from_path2(struct path *path, char *newname,
>>  		spin_unlock(&dcache_lock);
>>  		path_put(&root);
>>  		path_put(&ns_root);
>> +		/* Prepend "/proc" prefix if using internal proc vfs mount. */
>> +		if (!IS_ERR(sp) && (path->mnt->mnt_parent == path->mnt) &&
>> +		    (strcmp(path->mnt->mnt_sb->s_type->name, "proc") == 0)) {
>> +			sp -= 5;
>> +			if (sp >= newname)
>> +				memcpy(sp, "/proc", 5);
>> +			else
>> +				sp = ERR_PTR(-ENOMEM);
>> +		}
>>  	}
>>  	if (IS_ERR(sp))
>>  		error = PTR_ERR(sp);
>
> Above patch works. Please proceed. Thank you.
>
> Acked-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
>
> Why not to use path->mnt->mnt_sb->s_magic == PROC_SUPER_MAGIC rather than
> strcmp(path->mnt->mnt_sb->s_type->name, "proc") == 0 ?

Brain short circuit.

Eric

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