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Bug 983690 - libguestfs double free when kernel link fails during launch
Summary: libguestfs double free when kernel link fails during launch
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: libguestfs
Version: 6.5
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: rc
: ---
Assignee: Richard W.M. Jones
QA Contact: Virtualization Bugs
URL:
Whiteboard:
Depends On: 983218
Blocks:
TreeView+ depends on / blocked
 
Reported: 2013-07-11 17:49 UTC by Richard W.M. Jones
Modified: 2013-11-21 04:45 UTC (History)
7 users (show)

Fixed In Version: libguestfs-1.20.10-1.el6
Doc Type: Bug Fix
Doc Text:
(This was never in a released version and does not need to be documented)
Clone Of: 983218
Environment:
Last Closed: 2013-11-21 04:45:52 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)
Updated reproducer script. (1.25 KB, text/plain)
2013-07-11 18:14 UTC, Richard W.M. Jones 		no flags Details
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Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2013:1536 0 normal SHIPPED_LIVE Moderate: libguestfs security, bug fix, and enhancement update 2013-11-21 00:40:55 UTC

Description Richard W.M. Jones 2013-07-11 17:49:47 UTC 
+++ This bug was initially created as a clone of Bug #983218 +++

--- Additional comment from Richard W.M. Jones on 2013-07-11 12:25:20 EDT ---

I can see how a double free could occur.

The key observation is the last error message which was captured
in the guestfs handle:

(gdb) print g->last_error 
$5 = 0x7f296400c370 "link: /var/tmp/.guestfs-1002/kernel /var/tmp/.guestfs-1002/kernel.29013: Operation not permitted"

This errors occurs in hard_link_to_cached_appliance:

https://github.com/libguestfs/libguestfs/blob/af1c53d104180415a8584c48f19fd4ea7df224f5/src/appliance.c#L607

In hard_link_to_cached_appliance, along this error path
params.kernel would be allocated and then free (but not set
back to NULL).

Two levels higher up in the stack, the libvirt backend returns
from guestfs___build_appliance with an error:

https://github.com/libguestfs/libguestfs/blob/823628d41f898982979ab7dd53656377bef8ce1d/src/launch-libvirt.c#L232

and jumps to cleanup: which frees params.kernel again.  A
double-free.

The fix may be to set the kernel pointer to NULL after
freeing it the first time, but I need to systematically
check this code.

--- Additional comment from Richard W.M. Jones on 2013-07-11 12:53:49 EDT ---

Attached is a reproducer (although I think what it may be
reproducing is a related but ever so slightly different
bug in the same area of code).

It requires a working 'sudo' command in order to run
the following:

  sudo chattr +i /some/temporary/file

Install perl-Sys-Guestfs, download the attached script,
chmod +x the script, and just run it.

If it *segfaults* => bug reproduced.

If it prints "bug 983218 appears to be fixed" => bug fixed.

If it does/prints anything else, result is INVALID.  Please
let me know if this happens.

https://bugzilla.redhat.com/attachment.cgi?id=772313
Comment 2 Richard W.M. Jones 2013-07-11 18:14:57 UTC 
Created attachment 772357 [details]
Updated reproducer script.

Updated reproducer script.  Ignore link in previous comment.
Comment 3 Richard W.M. Jones 2013-07-18 14:04:11 UTC 
Upstream fix:
https://github.com/libguestfs/libguestfs/commit/ae78381287771a781f939f26a414fc8cfdc05fd6
Comment 4 bfan 2013-07-24 08:21:22 UTC 
Reproduced with libguestfs-1.20.9-6.el6.x86_64, using the attached script

[root@dhcp-9-42 home]# ./test.pl 
Segmentation fault (core dumped)
Comment 6 bfan 2013-08-06 07:25:14 UTC 
Verified with libguestfs-1.20.10-2.el6.x86_64

[root@intel-8400-8-2 home]# ./test.pl 
bug 983218 appears to be fixed

So change the status to verified
Comment 8 errata-xmlrpc 2013-11-21 04:45:52 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHSA-2013-1536.html
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