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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <1359118221.2496.150.camel@mfleming-mobl1.ger.corp.intel.com>
Date:	Fri, 25 Jan 2013 12:50:21 +0000
From:	Matt Fleming <matt.fleming@...el.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Lingzhu Xiang <lxiang@...hat.com>
Subject: Re: [RFC] efivars write(2) races

On Fri, 2013-01-25 at 00:25 +0000, 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...

Crap, yes. We'll have to jiggle the locking rules around to fix this
one.

> 	2) what's to prevent EFI_NOT_FOUND being hit twice?  Bad things
> will obviously happen in that case...

I'm not sure which execution path will trigger this? Oh, if we're
spinning for the spinlock in efivarfs_unlink() while another process
does a delete via efivarfs_file_write()? Yeah, that's gonna cause some
tears.

Thanks, Al.

--
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/