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Commit d4c0226 ("[dns] Support DNS search lists") introduced a
regression when handling CNAME records resolving to names longer than
the original name. The "end of name" offset stored in dns->offset was
not updated to reflect the length of the new name, causing
dns_question() to append the (empty) search suffix at an incorrect
offset within the name buffer, resulting in a mangled DNS name.
In the case of a CNAME record resolving to a name shorter than or
equal in length to the original name, then the mangling would occur in
an unused portion of the name buffer. In the common case of a name
server returning the A (or AAAA) record along with the CNAME record,
this would cause name resolution to succeed despite the mangling. (If
the name server did not return the A or AAAA record along with the
CNAME record, then the mangling would be revealed by the subsequent
invalid query packet.)
Reported-by: Nicolas Sylvain <nsylvain@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
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