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Bug 983691 - libguestfs double free when kernel link fails during launch
Summary: libguestfs double free when kernel link fails during launch
Keywords:
Status: CLOSED CURRENTRELEASE
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: libguestfs
Version: 7.0
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 17:50 UTC by Richard W.M. Jones
Modified: 2014-06-18 02:00 UTC (History)
8 users (show)

Fixed In Version: libguestfs-1.22.4-2.el7
Doc Type: Bug Fix
Doc Text:
Clone Of: 983218
Environment:
Last Closed: 2014-06-13 11:07:34 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)
Updated reproducer script. (1.25 KB, text/plain)
2013-07-11 18:15 UTC, Richard W.M. Jones 		no flags Details
View All

Description Richard W.M. Jones 2013-07-11 17:50:00 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 1 Richard W.M. Jones 2013-07-11 18:15:07 UTC 
Created attachment 772358 [details]
Updated reproducer script.

Updated reproducer script.  Ignore link in previous comment.
Comment 2 Richard W.M. Jones 2013-07-19 10:39:32 UTC 
Upstream fix is:
https://github.com/libguestfs/libguestfs/commit/ae78381287771a781f939f26a414fc8cfdc05fd6
Comment 3 bfan 2013-07-24 08:29:20 UTC 
Reproduce with libguestfs-1.22.4-1.el7.x86_64 using attached script

[root@intel-5405-32-3 home]# ./test.pl 
Segmentation fault (core dumped)
Comment 5 Lingfei Kong 2013-11-17 02:28:57 UTC 
Verified with libguestfs-1.22.6-15.el7

Steps:
1. Install perl-Sys-Guestfs-1.22.6-15.el7
2. Download test script from Comment 1
3. [lkong@rhel7libguestfs ~]$ sudo ./test.pl 
[sudo] password for lkong: 
bug 983218 appears to be fixed
Comment 6 Richard W.M. Jones 2013-11-17 09:32:42 UTC 
(In reply to Lingfei Kong from comment #5)
> 3. [lkong@rhel7libguestfs ~]$ sudo ./test.pl 

Note that the test script requires 'sudo'.  That doesn't mean
you should run the test script under sudo.  Run the
test program as you.
Comment 7 Lingfei Kong 2013-11-18 02:36:23 UTC 
(In reply to Richard W.M. Jones from comment #6)
> 
> Note that the test script requires 'sudo'.  That doesn't mean
> you should run the test script under sudo.  Run the
> test program as you.

Thanks for your reminding, I read the test script and understand that the test code need 'sudo' permission but not means that I should do the test under "sudo".
Comment 8 Ludek Smid 2014-06-13 11:07:34 UTC 
This request was resolved in Red Hat Enterprise Linux 7.0.

Contact your manager or support representative in case you have further questions about the request.
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