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Date: Thu, 29 Feb 2024 10:36:00 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] dns: check length field in tcp response message
On Thu, Feb 29, 2024 at 01:49:53PM +0300, Alexey Izbyshev wrote:
> 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
Thanks, applying!
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