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

[Andy Lutomirski]

On Wed, May 28, 2014 at 7:23 PM, Eric Paris <eparis@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx
>> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>> ---
>>  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@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/