Bug 1596795 (CVE-2018-10877) - CVE-2018-10877 kernel: out-of-bound access in ext4_ext_drop_refs function with a crafted ext4 image
Summary: CVE-2018-10877 kernel: out-of-bound access in ext4_ext_drop_refs function wit...
Alias: CVE-2018-10877
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
Depends On: 1596797 1596813 1602821
Blocks: 1596798
TreeView+ depends on / blocked
Reported: 2018-06-29 17:54 UTC by Laura Pardo
Modified: 2021-02-17 00:02 UTC (History)
44 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
A flaw was found in the Linux kernel ext4 filesystem. An out-of-bound access is possible in the ext4_ext_drop_refs() function when operating on a crafted ext4 filesystem image.
Clone Of:
Last Closed: 2019-06-10 10:31:02 UTC

Attachments (Terms of Use)

System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2018:2948 0 None None None 2018-10-30 09:02:50 UTC

Description Laura Pardo 2018-06-29 17:54:43 UTC
A flaw was found in Linux kernel ext4 filesystem. An out-of-bound access is possible in the ext4_ext_drop_refs() function when operating on a crafted ext4 filesystem image.




An upstream patch:


Comment 1 Laura Pardo 2018-06-29 17:55:56 UTC
Created kernel tracking bugs for this issue:

Affects: fedora-all [bug 1596797]

Comment 4 Justin M. Forbes 2018-07-16 14:34:24 UTC
This is fixed for Fedora with the 4.17.6 stable kernel update

Comment 8 Vladis Dronov 2018-07-18 15:07:38 UTC

While the flaw reproducer works when run as a privileged user (the "root"), this requires a mount of a certain filesystem image. An unprivileged attacker cannot do this even from a user+mount namespace:

$ unshare -U -r -m
# mount -t ext4 fs.img mnt/
mount: mnt/: mount failed: Operation not permitted.

The article https://lwn.net/Articles/652468/ discusses unprivileged user mounts and hostile filesystem images:
> ... for the most part, the mount() system call is denied to processes running
> within user namespaces, even if they are privileged in their namespaces.

It also states that unprivileged filesystem mounts are not allowed as of now in the Linux kernel and probably won't be allowed in a future. Until that such flaws are considered as not exploitable:

> There were no proposals for solutions to the hostile-filesystem problem.
> But, in the absence of some sort of assurance that they can be made safe,
> unprivileged filesystem mounts are unlikely to gain acceptance; even if the
> feature gets into the kernel, distributions would be likely to disable it.

On the other hand, there is a potential possibility that still an attacker can trick a regular user to mount a malicious filesystem image, like trick him to insert an usb-flash-drive with a forged filesystem to a desktop system which will auto-mount it. In case this results only in a system crash (a DoS due to, for example, a NULL pointer dereference) the flaw impact is low but it still exists. In case of a flaw which results in a privilege escalation the flaw's impact is higher.

So the Red Hat would still consider bugs which require mounting a filesystem image to exploit as security flaws, though with Low severity.

Comment 9 errata-xmlrpc 2018-10-30 09:02:29 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2018:2948 https://access.redhat.com/errata/RHSA-2018:2948

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