Summary

read-line blocks intermittantly on Atom based netbook

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Attachments

Description

This problem first shows up in:

9eef92115fba6034a98cc21ef740fd82ea52387b is the first bad commit commit 9eef92115fba6034a98cc21ef740fd82ea52387b Author: Peter Bex <peter.bex@xs4all.nl> Date: Sun Nov 18 21:03:51 2012 +0100

   Fix select() buffer overrun vulnerability by using POSIX poll() on systems that support it, leaving only those few systems vulnerable that don't (ie, only Windows).

I used the following code snippet to test. It took as much as 10 runs to trigger the bug sometimes:

=============CODE============= (use posix)

(define (conservative-read port)

 (let loop ((res '()))
   (if (not (eof-object? (peek-char port)))
       (loop (cons (read-char port) res))
       (apply conc (reverse res)))))

(define (cmd-run-with-stderr->list cmd . params)

  (let-values (((fh fho pid fhe) (if (null? params)
                                     (process* cmd)
                                     (process* cmd params))))
      (let loop ((curr (read-line fh))
                 (result  '()))
        (print "GOT HERE 1, curr=" curr)
        (let ((errstr (conservative-read fhe)))
          (print "GOT HERE 3, errstr=" errstr)
          (if (not (string=? errstr ""))
              (set! result (cons errstr result))))
        (print "GOT HERE 2, result=" result)
        (if (not (eof-object? curr))
            (begin
              (print "GOT HERE 4")
              (loop (read-line fh)
                    (cons curr result)))
            (begin
              (print "GOT HERE 5")
              (close-input-port fh)
              (close-input-port fhe)
              (close-output-port fho)
              (reverse result))))))

(print "Got: " (cmd-run-with-stderr->list "ls"))

Changes and comments

[2013-02-19 06:29:39 UTC] kiatoa wrote:

Replying to kiatoa: > This problem first shows up in: > > 9eef92115fba6034a98cc21ef740fd82ea52387b is the first bad commit > commit 9eef92115fba6034a98cc21ef740fd82ea52387b > Author: Peter Bex <peter.bex@xs4all.nl> > Date: Sun Nov 18 21:03:51 2012 +0100 > > Fix select() buffer overrun vulnerability by using POSIX poll() on systems that support it, leaving only those few systems vulnerable that don't (ie, only Windows). > > I used the following code snippet to test. It took as much as 10 runs to trigger the bug sometimes: > > =============CODE============= > (use posix) > > (define (conservative-read port) > (let loop ((res '())) > (if (not (eof-object? (peek-char port))) > (loop (cons (read-char port) res)) > (apply conc (reverse res))))) > > (define (cmd-run-with-stderr->list cmd . params) > (let-values (((fh fho pid fhe) (if (null? params) > (process* cmd) > (process* cmd params)))) > (let loop ((curr (read-line fh)) > (result '())) > (print "GOT HERE 1, curr=" curr) > (let ((errstr (conservative-read fhe))) > (print "GOT HERE 3, errstr=" errstr) > (if (not (string=? errstr "")) > (set! result (cons errstr result)))) > (print "GOT HERE 2, result=" result) > (if (not (eof-object? curr)) > (begin > (print "GOT HERE 4") > (loop (read-line fh) > (cons curr result))) > (begin > (print "GOT HERE 5") > (close-input-port fh) > (close-input-port fhe) > (close-output-port fho) > (reverse result)))))) > > (print "Got: " (cmd-run-with-stderr->list "ls")) >

To trigger the issue I ran the above code 10-20 times in a row. Generally the problem would show up in the first or second run but sometimes it would take many iterations before the problem occurred.

[2013-02-20 21:23:54 UTC] sjamaan wrote:

Interesting. I can reproduce the problem, but when I force the old "select()"-based implementation by ripping out HAVE_POSIX_POLL from Makefile.bsd, the same happens.

Seems this is more complicated than just the switch to poll.

[2013-02-20 21:45:40 UTC] sjamaan wrote:

I just did a bisect and it came up with a different commit:

fa9ccaa030cf7acaceb15378a4d6c33464f0eb1f is the first bad commit commit fa9ccaa030cf7acaceb15378a4d6c33464f0eb1f Author: Peter Bex <peter.bex@xs4all.nl> Date: Sat Feb 16 14:01:08 2013 +0100

   Get rid of overflow situation in read-line causing lines to be read wrong
   
   Signed-off-by: Christian Kellermann <ckeen@pestilenz.org>

That the bug was introduced somewhere in the read-line changes makes more sense to me.

[2013-02-20 21:51:05 UTC] zbigniew wrote:

But kiatoa said the problem occurs with 4.8.0.1, and that patch isn't in stability (obviously, since it just got applied 4 days ago!) Perhaps you are just not triggering the problem reliably?

[2013-02-20 22:23:26 UTC] sjamaan attached 0001-Fix-985-by-making-process-ports-consistent-with-TCP-.patch (description=A fix against master)

[2013-02-20 22:24:20 UTC] sjamaan wrote:

There's a possibility there are two distinct bugs here (or two different places where it manifested), since you ran into the problem with 4.8.0.1. Could you please try this patch against master?

[2013-02-20 22:48:34 UTC] sjamaan wrote:

Note: this bug only gets triggered if you run the program from a directory with sufficiently many files with sufficiently long filenames, I think (from the chicken source directory, for example)

[2016-08-25 21:25:43 UTC] sjamaan wrote:

Needs feedback

[2016-08-25 21:25:43 UTC] sjamaan changed status from new to assigned

[2016-08-25 21:25:43 UTC] sjamaan set difficulty to hard

[2016-08-25 21:25:43 UTC] sjamaan set owner to kiatoa