openssh bugs - Aug 2014 - [Bug 2263] New: sshd privsep monitor process doesn't handle SIGXFSZ signal

https://bugzilla.mindrot.org/show_bug.cgi?id=2263

            Bug ID: 2263
           Summary: sshd privsep monitor process doesn't handle SIGXFSZ
                    signal
           Product: Portable OpenSSH
           Version: 6.6p1
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: sshd
          Assignee: unassigned-bugs at mindrot.org
          Reporter: plautrba at redhat.com

FreeIPA allocates a random uid range for its use between 200k and 2G.
If an user with uid like 1280000008 logs in, the lastlog file size
jumps to almost 400G as lastlog is defined as a sparse file. 

The problem is when PAM with pam_limit module is used and the user has
fsize limit set. When sshd monitor process tries to write lastlog file,
it's already limited by pam_limit as a pam session is opened. And when
the lastlog file is bigger than the fsize limit, the process gets
SIGXFSZ signal and silently dies.

In other cases when lastlog entry can't be written, sshd logs the
problem and continues. Therefore I think that SIGXFSZ signal could be
ignored in the monitor process. atomicio() would set correctly errno
and lastlog_write_entry() would log the file size problem.

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned-bugs at mindrot.org |djm at mindrot.org
                 CC|                            |djm at mindrot.org

--- Comment #1 from Damien Miller <djm at mindrot.org> ---
Created attachment 2461
  --> https://bugzilla.mindrot.org/attachment.cgi?id=2461&action=edit
Ignore SIGXFSZ in preauth monitor

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
             Blocks|                            |2226

--- Comment #2 from Damien Miller <djm at mindrot.org> ---
This will be in openssh-6.7

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Petr Lautrbach <plautrba at redhat.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |---

--- Comment #3 from Petr Lautrbach <plautrba at redhat.com> ---
Unfortunatelly, it doesn't fix the issue. lastlog is written in
postauth phase so SIGXFSZ has to be ignored there.

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--- Comment #4 from Petr Lautrbach <plautrba at redhat.com> ---
Created attachment 2462
  --> https://bugzilla.mindrot.org/attachment.cgi?id=2462&action=edit
Ignore SIGXFSZ in postauth monitor child

Using this patch, the following message is logged in the described
scenario:

Aug 26 16:31:14 hulk.w.lan sshd[27852]: lastlog_write_entry: Error
writing to /var/log/lastlog: File too large

Reproducer:
- create an user with uid 1280000008
- set openssh to use pam
- set pam to use pam_limit.so
session     required      pam_limits.so

- add following line to /etc/security/limits.conf
user             hard    fsize           1024000

- try to login as user

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Petr Lautrbach <plautrba at redhat.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Attachment #2462|0                           |1
        is obsolete|                            |

--- Comment #5 from Petr Lautrbach <plautrba at redhat.com> ---
Created attachment 2463
  --> https://bugzilla.mindrot.org/attachment.cgi?id=2463&action=edit
Ignore SIGXFSZ in postauth monitor child

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #6 from Damien Miller <djm at mindrot.org> ---
applied - thanks

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED

--- Comment #7 from Damien Miller <djm at mindrot.org> ---
Close all bugs left open from 6.6 and 6.7 releases.

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