[prev in list] [next in list] [prev in thread] [next in thread] 

List:       oss-security
Subject:    [oss-security] Re: cve request: overlayfs: Fix dentry reference leak
From:       cve-assign () mitre ! org
Date:       2016-08-25 17:49:10
Message-ID: 20160825174910.2A2096C0BE4 () smtpvmsrv1 ! mitre ! org
[Download RAW message or body]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=ab79efab0a0ba01a74df782eb7fa44b044dae8b5
>  
> In ovl_copy_up_locked(), newdentry is leaked if the function exits through
> out_cleanup as this just to out after calling ovl_cleanup() - which doesn't
> actually release the ref on newdentry.
> 
> The out_cleanup segment should instead exit through out2 as certainly
> newdentry leaks - and possibly upper does also, though this isn't caught
> given the catch of newdentry.
> 
> Without this fix, something like the following is seen:
> 
> BUG: Dentry ffff880023e9eb20{i=f861,n=#ffff880023e82d90} still in use (1) [unmount of tmpfs \
>                 tmpfs]
> BUG: Dentry ffff880023ece640{i=0,n=bigfile}  still in use (1) [unmount of tmpfs tmpfs]
> 
> when unmounting the upper layer after an error occurred in copyup.
> 
> An error can be induced by creating a big file in a lower layer with
> something like:
> 
> dd if=/dev/zero of=/lower/a/bigfile bs=65536 count=1 seek=$((0xf000))
> 
> to create a large file (4.1G). Overlay an upper layer that is too small
> (on tmpfs might do) and then induce a copy up by opening it writably.
> 
> === POC Exploit ===
> This can be reproduced in a DevOps environment when the docker runtime storage is on \
> overlayfs over xfs as a local DoS. An attacker access to a developer account could run a \
> crafted image from elsewhere like docker by creating a big file in the container filesystem \
> and try to read it running by any user like below by forcing xfs_file_open() returns -EFBIG,
> 
> $ cat Dockerfile
> FROM fedora
> USER nobody
> RUN dd if=/dev/zero of=/home/nobody/bigfile bs=1024k seek=2046 count=1
> ADD open /home/nobody
> CMD ["/home/nobody/open", "/home/nobody/bigfile"]
> 
> and possibly trigger kernel dentry leaks inside the container that will eventually running \
> out of kernel resources for other developers. Hence, a local DoS.

Use CVE-2015-8953.

- -- 
CVE Assignment Team
M/S M300, 202 Burlington Road, Bedford, MA 01730 USA
[ A PGP key is available for encrypted communications at
  http://cve.mitre.org/cve/request_id.html ]
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1
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=Cr9c
-----END PGP SIGNATURE-----


[prev in list] [next in list] [prev in thread] [next in thread]