linux-kernel - Re: [PATCH 2/2] debugfs: only allow root access to debugging interfaces

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Message-ID: <4D640133.9020901@caviumnetworks.com>
Date:	Tue, 22 Feb 2011 10:32:19 -0800
From:	David Daney <ddaney@...iumnetworks.com>
To:	Kees Cook <kees.cook@...onical.com>
CC:	linux-kernel@...r.kernel.org, Eugene Teo <eugeneteo@...nel.sg>,
	Ralph Campbell <infinipath@...gic.com>,
	Roland Dreier <roland@...nel.org>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Miklos Szeredi <miklos@...redi.hu>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Neil Brown <neilb@...e.de>, Matthew Wilcox <matthew@....cx>,
	James Morris <jmorris@...ei.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Eric Paris <eparis@...isplace.org>,
	Nick Piggin <npiggin@...nel.dk>, Arnd Bergmann <arnd@...db.de>,
	Ian Campbell <ian.campbell@...rix.com>,
	Jarkko Sakkinen <ext-jarkko.2.sakkinen@...ia.com>,
	Tejun Heo <tj@...nel.org>,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH 2/2] debugfs: only allow root access to debugging interfaces

On 02/22/2011 10:16 AM, Kees Cook wrote:
> Har har, I forgot --compose to "git send-email".
>
> Anyway, with the continuing deluge of bugs in the "debug" filesystem, I
> would like to make that filesystem's root directory mode 0700 by default
> since it's filled with crazy stuff that regular users do not need to see.
>
> Better to try to just close the door completely on all the stuff in there.
> It is, after all, supposed to only be used for debugging, right?
>

It depends if you consider use of ftrace and kprobes 'debugging'.  In 
any event, you really have to be root to be able to manipulate them.

I can currently do 'cat /sys/kernel/debug/tracing/trace' as a normal 
user.  With your change I don't think it would be possible.  This is not 
something I often (ever) do, but it is a change.

David Daney


> -Kees
>
> On Tue, Feb 22, 2011 at 10:09:58AM -0800, Kees Cook wrote:
>> Block access to the potentially dangerous debugging interfaces in
>> the debugfs filesystem.
>>
>> Signed-off-by: Kees Cook<kees.cook@...onical.com>
>> ---
>>   fs/debugfs/inode.c |    2 +-
>>   1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
>> index 3cb33c3..83c61a3 100644
>> --- a/fs/debugfs/inode.c
>> +++ b/fs/debugfs/inode.c
>> @@ -133,7 +133,7 @@ static int debug_fill_super(struct super_block *sb, void *data, int silent)
>>   	static struct tree_descr debug_files[] = {{""}};
>>
>>   	return simple_fill_super(sb, DEBUGFS_MAGIC, debug_files,
>> -				 S_IWUSR | S_IRUGO | S_IXUGO);
>> +				 S_IRWXU);
>>   }
>>
>>   static struct dentry *debug_mount(struct file_system_type *fs_type,
>> --
>> 1.7.2.3
>>
>> --
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