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Message-ID: <45da412c2c78a6d4c02023b172a778aa@ispras.ru>
Date: Thu, 29 Feb 2024 13:49:53 +0300
From: Alexey Izbyshev <izbyshev@...ras.ru>
To: musl@...ts.openwall.com
Cc: Alexey Kodanev <aleksei.kodanev@...l-sw.com>
Subject: Re: [PATCH] dns: check length field in tcp response message
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
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