Re: [musl] [PATCH] dns: check length field in tcp response message

[Alexey Izbyshev <izbyshev@ispras.ru>]

On 2023-05-08 19:25, Alexey Izbyshev wrote:
> On 2023-03-22 16:16, Rich Felker wrote:
>> On Wed, Mar 22, 2023 at 03:29:16PM +0300, Alexey Kodanev wrote:
>>> The received length field in the message may be greater than the
>>> size of the 'answer' buffer in which the message resides. Currently,
>>> ABUF_SIZE is 768. And if we get a larger 'alen', it will result
>>> in an out-of-bounds reading during parsing, because 'alen' will
>>> be passed to __dns_parse() later:
>>> 
>>>     __dns_parse(abuf[i], alens[i], dns_parse_callback, &ctx);
>>> 
>>> To fix this, limit 'alen' to the size of the received buffer.
>>> ---
>>>  src/network/res_msend.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>> 
>>> diff --git a/src/network/res_msend.c b/src/network/res_msend.c
>>> index fef7e3a2..291853de 100644
>>> --- a/src/network/res_msend.c
>>> +++ b/src/network/res_msend.c
>>> @@ -297,6 +297,7 @@ int __res_msend_rc(int nqueries, const unsigned 
>>> char *const *queries,
>>>  			int rcode = answers[i][3] & 15;
>>>  			if (rcode != 0 && rcode != 3)
>>>  				goto out;
>>> +			if (alen > asize) alen = asize;
>>> 
>>>  			/* Storing the length here commits the accepted answer.
>>>  			 * Immediately close TCP socket so as not to consume
>>> --
>>> 2.25.1
>> 
>> This is incorrect. It breaks res_send, whose contract is to return the
>> full answer length even if it did not fit, so that the caller can
>> retry with the appropriate size.
>> 
>> Instead, name_from_dns just needs to clamp the value before passing it
>> to __dns_parse.
>> 
> Not only name_from_dns, but also getnameinfo. The patch is attached.
> 
Pinging due to the approaching release. Did the patch fall through 
cracks?

Thanks,
Alexey