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List:       syslog-ng
Subject:    [syslog-ng] [Bug 8] New: syslog-ng hangs writing to /dev/ttyN
From:       bugzilla () www ! balabit ! com
Date:       2007-12-25 14:27:29
Message-ID: bug-8-3 () https ! bugzilla ! balabit ! com/
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https://bugzilla.balabit.com/show_bug.cgi?id=8

           Summary: syslog-ng hangs writing to /dev/ttyN
           Product: syslog-ng
           Version: 2.0.x
          Platform: PC
               URL: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=397650
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: unspecified
         Component: syslog-ng
        AssignedTo: bazsi@balabit.hu
        ReportedBy: sasa@debian.org
Type of the Report: bug
   Estimated Hours: 0.0


Created an attachment (id=4)
 --> (https://bugzilla.balabit.com/attachment.cgi?id=4)
Patch to prevent hanging

From bugs.debian.org:

(This is the same problem reported against syslog-ng in Gentoo at
https://bugs.gentoo.org/show_bug.cgi?id=154465 -- this contains
a patch which fixes the problem with a similar approach to that
taken in sysklogd.)

When syslog-ng writes to a tty under Linux, for example as a
result of a usertty directive, the write syscall to
/dev/ttyN can ocassionally block indefinitely.  One
situation when this occurs is when the user has set XOFF
(perhaps with Ctrl-S or Scroll Lock).

Aside from the fact that this obvious prevents any further
log messages from being written, /dev/log's buffer
eventually fills up causing other programs to block writing
to /dev/log.  In extremis, this can render a machine
inaccesible when ssh, etc., all block preventing access.


Reproducible: Always

Steps to Reproduce:

1. Check that there is a usertty("*") directive for (say) kern.emerg logs
2. Ensure syslog-ng is running
3. On console, press Scroll Lock
4. Log something, e.g. logger -p kern.emerg 'Foo'.
5. Repeat #4 many times; eventually it will hang trying to log


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