linux-kernel - Re: [RFC] efivars write(2) races

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 25 Jan 2013 13:18:03 +0000
From:	Matt Fleming <matt.fleming@...el.com>
To:	Lingzhu Xiang <lxiang@...hat.com>
Cc:	Al Viro <viro@...IV.linux.org.uk>, linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jeremy Kerr <jeremy.kerr@...onical.com>
Subject: Re: [RFC] efivars write(2) races

On Fri, 2013-01-25 at 11:50 +0800, Lingzhu Xiang wrote:
> On 01/25/2013 08:25 AM, Al Viro wrote:
> > 	1) process A does write() on efivars file, reaches ->get_variable(),
> > gets newdatasize set, drops efivars->lock and loses CPU before an attempt to
> > grab ->i_mutex.  process B comes and does the same thing, replacing the
> > variable contents.  Then it grabs ->i_mutex, updates size, drops ->i_mutex
> > and buggers off.  At which point A gets CPU back and proceeds to set size
> > to whatever would be valid for its write.  Only the value is bogus now...
> 
> There are a few other things that makes size bogus now.
> 
> 1. truncate() never touches nvram but pretends to be changing size.

Good catch. Looks like we need to provide an implementation for this.

> 2. Empty files come back with non-zero size after remount. They are imported
>    from sysfs when mounting.

Eeek. The return value of get_variable() isn't checked in
efivarfs_fill_super().

> 3. Arguably reading empty files could just return empty instead of returning
>    EIO/EFI_NOT_FOUND from firmware. 

Yeah, I think Jeremy has a patch to fix this.

> 4. EFI_VARIABLE_APPEND_WRITE with EFI_OUT_OF_RESOURCES truncates size but you
>    can still read its content.

I'm not sure what you mean by this. Could you please explain?

Thanks for the feedback.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/