From: Lingzhu Xiang <lxiang-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
Cc: Matt Fleming
<matt.fleming-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [RFC] efivars write(2) races
Date: Fri, 25 Jan 2013 11:50:56 +0800 [thread overview]
Message-ID: <51020120.5000500@redhat.com> (raw)
In-Reply-To: <20130125002552.GC4503-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
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.
2. Empty files come back with non-zero size after remount. They are imported
from sysfs when mounting.
3. Arguably reading empty files could just return empty instead of returning
EIO/EFI_NOT_FOUND from firmware.
4. EFI_VARIABLE_APPEND_WRITE with EFI_OUT_OF_RESOURCES truncates size but you
can still read its content.
WARNING: multiple messages have this Message-ID (diff)
From: Lingzhu Xiang <lxiang@redhat.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Matt Fleming <matt.fleming@intel.com>,
linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC] efivars write(2) races
Date: Fri, 25 Jan 2013 11:50:56 +0800 [thread overview]
Message-ID: <51020120.5000500@redhat.com> (raw)
In-Reply-To: <20130125002552.GC4503@ZenIV.linux.org.uk>
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.
2. Empty files come back with non-zero size after remount. They are imported
from sysfs when mounting.
3. Arguably reading empty files could just return empty instead of returning
EIO/EFI_NOT_FOUND from firmware.
4. EFI_VARIABLE_APPEND_WRITE with EFI_OUT_OF_RESOURCES truncates size but you
can still read its content.
next prev parent reply other threads:[~2013-01-25 3:50 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-25 0:25 [RFC] efivars write(2) races Al Viro
2013-01-25 0:25 ` Al Viro
[not found] ` <20130125002552.GC4503-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
2013-01-25 3:50 ` Lingzhu Xiang [this message]
2013-01-25 3:50 ` Lingzhu Xiang
[not found] ` <51020120.5000500-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2013-01-25 13:18 ` Matt Fleming
2013-01-25 13:18 ` Matt Fleming
[not found] ` <1359119883.2496.156.camel-ZqTwcBeJ+wsBof6jY8KHXm7IUlhRatedral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2013-01-28 2:38 ` Lingzhu Xiang
2013-01-28 2:38 ` Lingzhu Xiang
[not found] ` <5105E4A3.9040102-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2013-01-28 12:38 ` Matt Fleming
2013-01-28 12:38 ` Matt Fleming
[not found] ` <1359376730.8282.20.camel-ZqTwcBeJ+wsBof6jY8KHXm7IUlhRatedral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2013-01-29 2:30 ` Lingzhu Xiang
2013-01-29 2:30 ` Lingzhu Xiang
2013-01-25 12:50 ` Matt Fleming
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