Bug 1596842 (CVE-2018-10882)

Summary: CVE-2018-10882 kernel: stack-out-of-bounds write infs/jbd2/transaction.c
Product: [Other] Security Response Reporter: Laura Pardo <lpardo>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED ERRATA QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: abhgupta, airlied, aquini, bhu, bskeggs, dbaker, dhoward, ewk, fhrbata, hdegoede, hkrzesin, hwkernel-mgr, iboverma, ichavero, itamar, jarodwilson, jforbes, jglisse, jkacur, john.j5live, jokerman, jonathan, josef, jross, jwboyer, kernel-maint, kernel-mgr, labbott, lgoncalv, linville, matt, mchehab, mcressma, mjg59, nmurray, plougher, rvrbovsk, skozina, slawomir, steved, sthangav, trankin, vdronov, williams, wmealing
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Fixed In Version: Doc Type: If docs needed, set a value
Doc Text:
A flaw was found in the Linux kernel's ext4 filesystem. A local user can cause an out-of-bound write in the fs/jbd2/transaction.c code, a denial of service, and a system crash by unmounting a crafted ext4 filesystem image.
Story Points: ---
Clone Of: Environment:
Last Closed: 2019-06-10 10:31:15 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Bug Depends On: 1596843, 1596844, 1609237    
Bug Blocks: 1596845    

Description Laura Pardo 2018-06-29 19:05:57 UTC
A flaw was found in the Linux kernel's ext4 file system. A local user can cause an out-of-bound write in in fs/jbd2/transaction.c code, which can lead to memory corruption.  This can mean that the memory can be corrupted to create a denial of service, and a system crash or privilege escalation by unmounting a crafted ext4 filesystem image.



An upstream patch:


Comment 1 Laura Pardo 2018-06-29 19:07:22 UTC
Created kernel tracking bugs for this issue:

Affects: fedora-all [bug 1596843]

Comment 4 Justin M. Forbes 2018-07-16 14:41:13 UTC
This is fixed for Fedora with the 4.17.6 stable kernel update

Comment 8 Vladis Dronov 2018-07-27 10:51:13 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 09:03:12 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