From: Barry Bond <barrybo@microsoft.com>
To: "musl@lists.openwall.com" <musl@lists.openwall.com>
Subject: [musl] Behavior change in getaddrbyname() with AF_UNSPEC
Date: Sat, 14 Jan 2023 22:56:28 +0000 [thread overview]
Message-ID: <DM6PR21MB16119FB8E9D5AE1E364D42ABB6C39@DM6PR21MB1611.namprd21.prod.outlook.com> (raw)
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This is related to this change: https://git.musl-libc.org/cgit/musl/commit/?id=5cf1ac2443ad0dba263559a3fe043d929e0e5c4c made back in 2020.
In the repro case, getaddrbyname() with AF_UNSPEC sends out two requests, but only gets back a single response, with the ipv4 address. There is no ipv6 on the network.
name_from_dns() contains the relevant code. After __res_msend_rc() returns, 'nq' is 2, and 'alens' is [96, 0], indicating that there was an ipv4 response of 96 bytes, but no response for ipv6. Then the validation code runs:
for (i=0; i<nq; i++) {
if (alens[i] < 4 || (abuf[i][3] & 15) == 2) return EAI_AGAIN;
if ((abuf[i][3] & 15) == 3) return 0;
if ((abuf[i][3] & 15) != 0) return EAI_FAIL;
}
and the result is EAI_AGAIN, because alens[1]==0.
Before this patch, the code would have parsed the ipv4 response via __dns_parse(), failed to parse the empty second response because alens[1]<12, and the function would return with ctx.cnt==1.
I propose adding one new check at the top of the for() loop:
if (alens[i] == 0) continue; /* response timed out */
Thanks!
Barry - Microsoft Azure Sphere
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next reply other threads:[~2023-01-14 22:56 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-14 22:56 Barry Bond [this message]
2023-01-18 15:26 ` Rich Felker
2023-01-19 14:58 ` [musl] RE: [EXTERNAL] " Barry Bond
2023-01-23 1:34 ` [musl] " Barry Bond
2023-01-24 8:54 ` Rich Felker
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