Better handling of fds 0/1/2 #1233
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Discovered when mosh-server is started with a closed stderr, /dev/urandom is opened on fd 2, and the daemon code reopens fd 2 on /dev/null. In that case, mosh-server loops forever throwing a non-fatal exception.
Fixes unpleasant behavior in mosh-server when, say, stderr is closed.
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@cgull would you mind rebasing this PR? |
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I ran into this while working on what is now #1232.
mosh-serverdoes not adequately handle the problem of standard file descriptors being closed. In my development, er, over two years ago, I ran into a situation wheremosh-serverhad started with fd 2 closed, it opened/dev/urandomon fd 2, and then later reopened fd 2 on/dev/null. Then, when it tried to actually read fd 2 to get entropy, it got 0 bytes instead, and got caught in a never-ending loop involving an exception being caught and the action being retried. I don't remember for sure, but I think that left the Mosh session hung inmosh.This work does 3 things:
CryptoExceptionthrown on failure to read fatal-- there's no point in continuing if we can't get a random seed./dev/nullon the closed fd,dup2()it to 0/1/2, and then close the temporary file. Oops.I can't now reproduce the hang, unfortunately. Both Mosh and my OSes have changed since hten. I tried to write a test for this issue, but between not being able to reproduce the problem and
mosh-serverbeing difficult to keep track of because it double-forks, I've given up for now. Should any of you doubt there's a problem,strace -o strace.log -f mosh-server new 2>&-will convince you fairly quickly. And while I didn't experience any actual crypto failure, even the possibility of confused crypto code is a rather bad smell.(Plus, we burned a couple of weeks chasing this problem down at $WORK once.)