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Posted to bugs@apr.apache.org by bu...@apache.org on 2015/03/06 11:13:25 UTC
[Bug 57671] New: apr_proc_detach() should close ALL file descriptors
https://bz.apache.org/bugzilla/show_bug.cgi?id=57671
Bug ID: 57671
Summary: apr_proc_detach() should close ALL file descriptors
Product: APR
Version: 1.4.5
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P2
Component: APR
Assignee: bugs@apr.apache.org
Reporter: hahn@univention.de
apr_proc_detach() (as called by apache-2.2.22) does only close STDIN, STDOUT,
STDERR, but not all other (open) file descriptors.
This is problematic when apache2 is restarted from an unclean environment,
where other file descriptors are opened and are pipes, as this happens for
example with <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=713967>: As the
forked Apache process inherits the pipe, it is considered a potential writer,
so any reading will block indefinitely instead of getting an EOF.
(Daemons not closing all file descriptors is a common problem, for which
DebConf has an extra FQA entry:
<http://www.fifi.org/doc/debconf-doc/tutorial.html#AEN198>)
As far as I know daemons should close all file descriptors:
- <http://linux.die.net/man/1/daemonize>
- <http://stackoverflow.com/questions/17954432/creating-a-daemon-in-linux>
- <http://en.wikipedia.org/wiki/Daemon_(computing)#Creating>
Closing all open file descriptors is somehow problematic, as there is no
portable function for it. Because of that daemons normally implement a loop to
close all FDs:
int x;
for (x = sysconf(_SC_OPEN_MAX); x>0; x--)
close (x);
For Linux one can optimize that by using apr_dir_open(..., "/proc/self/fd",
...) to only close the open FDs.
IMHO apr_proc_detach() should implement the generic close-all-FDs semantic
instead of only Apache-httpd doing it.
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[Bug 57671] New function for apr_proc_detach() + close ALL file
descriptors
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=57671
Yann Ylavic <yl...@gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Version|1.4.5 |HEAD
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[Bug 57671] apr_proc_detach() should close ALL file descriptors
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=57671
--- Comment #1 from Philipp Hahn <ha...@univention.de> ---
Created attachment 32548
--> https://bz.apache.org/bugzilla/attachment.cgi?id=32548&action=edit
Demo-implementation of close_fds()
gcc -Wall -o apache-closefd apache-closefd.c && ./apache-closefd 42>/dev/null
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[Bug 57671] apr_proc_detach() should close ALL file descriptors
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=57671
--- Comment #2 from Yann Ylavic <yl...@gmail.com> ---
apr_proc_detach() does exactly what it is meant to: make the current process
detach from the terminal (close STDIN/OUT/ERR) and, if daemonize is specified
(not the daemonize tool!), make the current process have its own session (go
background).
Should it close all open descriptors now that could/would break existing
applications, those which currently open file descriptors before
apr_proc_detach() and use them after (note that apr_proc_detach() already takes
care of not closing the standard descriptors, but rather reopen them so that
next opened descriptors won't "hijack" STDIN/OUT/ERR).
Maybe the APR could introduce a new function for this, but IMHO this already as
simple as opening fds on a dedicated pool which could then be cleared before
apr_proc_detach() is called. For fds that are not handled by the APR, it seems
quite tricky to let the APR close them...
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[Bug 57671] New function for apr_proc_detach() + close ALL file
descriptors
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=57671
Jeff Trawick <tr...@apache.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |WONTFIX
Status|NEW |RESOLVED
--- Comment #3 from Jeff Trawick <tr...@apache.org> ---
I also don't think apr has a role here to free arbitrary handles (other devs
can of course disagree and re-open).
The best place to address this issue is in the caller of httpd, but maybe httpd
could have a role, controlled by some -Dxxx command-line arg. (Does httpd and
its arbitrary plug-in modules have no fds it needs to preserve across the
detach? I don't understand how any code would know, but that's not a concern
for this apr bug ;) )
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[Bug 57671] New function for apr_proc_detach() + close ALL file
descriptors
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=57671
Yann Ylavic <yl...@gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ylavic.dev@gmail.com
Severity|normal |enhancement
Summary|apr_proc_detach() should |New function for
|close ALL file descriptors |apr_proc_detach() + close
| |ALL file descriptors
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