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DescriptionRichard 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 2Richard 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 3Richard W.M. Jones
2013-07-18 14:04:11 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