linux-kernel - Re: [PATCH v2 1/2] auditsc: audit_krule mask accesses need bounds checking

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]

Date:	Wed, 28 May 2014 19:27:11 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Eric Paris <eparis@...hat.com>
Cc:	Philipp Kern <pkern@...gle.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. J. Lu" <hjl.tools@...il.com>,
	"security@...nel.org" <security@...nel.org>,
	Greg Kroah-Hartman <greg@...ah.com>, linux-audit@...hat.com,
	stable@...r.kernel.org
Subject: Re: [PATCH v2 1/2] auditsc: audit_krule mask accesses need bounds checking

On Wed, May 28, 2014 at 7:23 PM, Eric Paris <eparis@...hat.com> wrote:
> On Wed, 2014-05-28 at 18:44 -0700, Andy Lutomirski wrote:
>> Fixes an easy DoS and possible information disclosure.
>>
>> This does nothing about the broken state of x32 auditing.
>>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Andy Lutomirski <luto@...capital.net>
>> ---
>>  kernel/auditsc.c | 27 ++++++++++++++++++---------
>>  1 file changed, 18 insertions(+), 9 deletions(-)
>>
>> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
>> index f251a5e..7ccd9db 100644
>> --- a/kernel/auditsc.c
>> +++ b/kernel/auditsc.c
>> @@ -728,6 +728,22 @@ static enum audit_state audit_filter_task(struct task_struct *tsk, char **key)
>>       return AUDIT_BUILD_CONTEXT;
>>  }
>>
>> +static bool audit_in_mask(const struct audit_krule *rule, unsigned long val)
>> +{
>> +     int word, bit;
>> +
>> +     if (val > 0xffffffff)
>> +             return false;
>
> Why is this necessary?

To avoid an integer overflow.  Admittedly, this particular overflow
won't cause a crash, but it will cause incorrect results.

>
>> +
>> +     word = AUDIT_WORD(val);
>> +     if (word >= AUDIT_BITMASK_SIZE)
>> +             return false;
>
> Since this covers it and it extensible...
>
>> +
>> +     bit = AUDIT_BIT(val);
>> +
>> +     return rule->mask[word] & bit;
>
> Returning an int as a bool creates worse code than just returning the
> int.  (although in this case if the compiler chooses to inline it might
> be smart enough not to actually convert this int to a bool and make
> worse assembly...)   I'd suggest the function here return an int.  bools
> usually make the assembly worse...

I'm ambivalent.  The right assembly would use flags on x86, not an int
or a bool, and I don't know what the compiler will do.

--Andy
--
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/