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os/exec: fd leak on NetBSD #3955

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4a6f656c opened this issue Aug 15, 2012 · 13 comments
Closed

os/exec: fd leak on NetBSD #3955

4a6f656c opened this issue Aug 15, 2012 · 13 comments
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FrozenDueToAge OS-NetBSD Suggested Issues that may be good for new contributors looking for work to do.
Milestone
Unplanned

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@4a6f656c
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What steps will reproduce the problem?

  Run tests for os/exec.

What is the expected output? What do you see instead?

  Additional part of test shows that an extra file descriptor of 
  type DTYPE_MISC is leaked to the child.

This is related to opening /dev/urandom, which results in a cloned file descriptor. The
underlying cause is due to Read in crypto/rand/rand_unix.go having an os.Open() call,
but no matching Close() call. This means that anything that does rand.Reader.Read() will
open a file descriptor that never gets closed (and in NetBSD we get one that is cloned).
My current guess is that FD_CLOEXEC does not work for cloned descriptors, however
further digging is required...
@rsc
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rsc commented Jan 31, 2013

Comment 2:

Labels changed: added priority-later, removed priority-soon.

@rsc
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rsc commented Jul 30, 2013

Comment 3:

Labels changed: added go1.2.

@rsc
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rsc commented Sep 10, 2013

Comment 4:

What do you mean by "cloned" file descriptor?

@rsc
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rsc commented Sep 10, 2013

Comment 5:

Labels changed: added testing.

@rsc
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rsc commented Sep 11, 2013

Comment 6:

Labels changed: added go1.2maybe, removed go1.2.

@rsc
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rsc commented Oct 2, 2013

Comment 7:

Labels changed: added go1.3, removed go1.2maybe.

@rsc
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rsc commented Dec 4, 2013

Comment 8:

Labels changed: added release-go1.3.

@rsc
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rsc commented Dec 4, 2013

Comment 9:

Labels changed: removed go1.3.

@rsc
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rsc commented Dec 4, 2013

Comment 10:

Labels changed: added repo-main.

@gopherbot
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Comment 11 by justin@specialbusservice.com:

re "What do you mean by "cloned" file descriptor?" - I think the NetBSD implementation
must be using the clone(2) syscall, which is there for compatibility with Linux, rather
than fork(2), and that results in issues with cloexec. I will look into this.

@4a6f656c
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Comment 12:

There is a kernel function that clones file descriptors (search for fd_clone):
  http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/kern/kern_descrip.c?rev=1.224
This particular function sets the file type to DTYPE_MISC, which is the same as the type
that is being leaked. There are a handful of places where this function is used in the
NetBSD kernel - one of which is the rndopen() function (in sys/dev/rndpseudo.c), which
is used when the /dev/urandom device is opened.
I (or someone else) still needs to dig further, however this cloned descriptor either
does not have FD_CLOEXEC set and/or we are not setting it, which results in the file
descriptor leak when Go does a fork/exec.

@ianlancetaylor
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Comment 13:

Setting to Release-None as this does not seem like a serious bug.  But a CL would
certainly be welcome.

Labels changed: added os-netbsd, suggested, release-none, removed priority-later, testing, release-go1.3.

@4a6f656c 4a6f656c added accepted Suggested Issues that may be good for new contributors looking for work to do. labels Apr 2, 2014
@rsc rsc removed the os-netbsd label Apr 10, 2015
@rsc rsc added this to the Unplanned milestone Apr 10, 2015
@bradfitz
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Fixed by requiring NetBSD 8+ for Go 1.10.

Documentation bug is #22911

@golang golang locked and limited conversation to collaborators Nov 28, 2018
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@bradfitz @rsc @ianlancetaylor @4a6f656c @gopherbot