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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D">Hi ,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D"> I have verified this commit, it works well. When can we got a formal release includes this commit?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D">thanks.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Matt Johnston [mailto:matt@ucc.asn.au]
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<b>Sent:</b> 2016</span><span style="font-size:10.0pt;font-family:SimSun">��</span><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">4</span><span style="font-size:10.0pt;font-family:SimSun">��</span><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">29</span><span style="font-size:10.0pt;font-family:SimSun">��</span><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">
<span lang="EN-US">23:18<br>
<b>To:</b> ZHANG Hui P<br>
<b>Cc:</b> dropbear@ucc.asn.au<br>
<b>Subject:</b> Re: a bug detected in dropbear v071<o:p></o:p></span></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Hi,<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">I think this problem should be solved by the commit<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><a href="https://secure.ucc.asn.au/hg/dropbear/rev/432b0a030fd6">https://secure.ucc.asn.au/hg/dropbear/rev/432b0a030fd6</a><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Thank you for the detailed report.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Cheers,<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Matt<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">On Wed 20/4/2016, at 2:44 pm, ZHANG Hui P <<a href="mailto:Hui.P.Zhang@alcatel-sbell.com.cn">Hui.P.Zhang@alcatel-sbell.com.cn</a>> wrote:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif"">Hi:<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif""> I am a software engineer of Alcatel-Lucent. In our product we use dropbear v071 under the OS:
Linux version 3.4.24. At most time it works perfectly, but recently we got a problem: sometimes a child-process of dropbear occupied nearly 100% CPU (we use ARM1176, single-core). After I investigated it ,I found it is cause by a misuse of KEX_REKEY_TIMEOUT.<o:p></o:p></span></p>
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<p class="MsoNormal" style="text-indent:21.0pt"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif"">KEX_REKEY_TIMEOUT is defined as 8hours. that means when a session lasts more than 8 hours, the server and client will re-exchange
their KEY for security reason. The timestamp of last-time KEY-EXCHANGED is recorded in variable "ses.kexstate.lastkextime".<span class="apple-converted-space"> </span><o:p></o:p></span></p>
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<p class="MsoNormal" style="text-indent:21.0pt"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif""> The child dropbear process decides the "timeout" parameter of "select" function by calling "select_timeout". we can see it checks
the timeout-events like KEX_REKEY_TIMEOUT, AUTH_TIMEOUT, keepalive_secs. If there is a timeout occurs, the "update_timeout" function returns a negative value, then "select_timeout" modifies it to ZREO by this:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif"">/* clamp negative timeouts to zero - event has already triggered */<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif""> return MAX(timeout, 0);<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif""> if "select_timeout" returns ZERO, the next "select" call (in "session_loop") will return immediately. Then it will check timeout events by this:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif"">/* check for auth timeout, rekeying required etc */<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif""> checktimeouts();<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif""> in the function " checktimeouts ", when it find the timeout is reached or to many data has been sent, it will send a SSH_MSG_KEXINIT message to peer. Normally
this message will trigger a new KEY-EXCHANGE. However, when there is a network problem that the peer can't receive the message , this bug occurs: the timestamp ses.kexstate.lastkextime is only updated by calling "switch_keys"-->" kexinitialise ", unfortunately
this calling sequence is driven by ssh-messages, either SSH_MSG_KEXDH_INIT or SSH_MSG_NEWKEYS. When there is no ssh-message received , the child dropbear process enters dead-loop "select" with ZERO-timeout parameter caused by KEX_REKEY_TIMEOUT.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif"">> So there is a very simple way to reproduce this bug: first define the KEX_REKEY_TIMEOUT as small as possible( I set it to 8 seconds), then start a ssh-session
, the child dropbear process is forked. then plug out the network wire, after 8 seconds the child dropbear thread will occupy 100% CPU. Could you kindly check it? thanks.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal" style="text-indent:21.0pt"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri","sans-serif"">Best regards<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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