Old Linux Kernel Bug Discovered
The bug was introduced back in 2009 and has been lurking around all this time.
Alexander Popov, one of the winners of the 2016 Linux Foundation Training (LiFT) scholarship, has discovered a very old bug in the Linux kernel that can affect modern systems.
Popov wrote on a mailing list, “This is an announcement of CVE-2017-2636, which is a race condition in the n_hdlc Linux kernel driver (drivers/tty/n_hdlc.c). It can be exploited to gain a local privilege escalation. This driver provides HDLC serial line discipline and comes as a kernel module in many Linux distributions, which have CONFIG_N_HDLC=m in the kernel config.”
Popov fixed the issue by using “standard kernel linked list protected by a spinlock and got rid of n_hdlc.tbuf. In the case of transmission error, the current data buffer is put after the head of tx_buf_list,” he wrote on the mailing list.
The issue is affecting major distributions, including Red Hat Enterprise Linux. According to a Red Hat Bugzilla submission, although RHEL 5 is unaffected, the bug does affect the Linux kernel packages shipped with Red Hat Enterprise Linux 6 and 7 and Red Hat Enterprise MRG 2. Because this issue is rated important, it has been scheduled to be fixed in future updates for the respective releases. Canonical has already released a patch; SUSE is working on it.
The bug is old, and the module is used in really old hardware; even if the module is shipped with modern Linux distributions, it’s never loaded by default. However, the module is automatically loaded “if an unprivileged user opens a pseudoterminal and calls TIOCSETD ioctl for it setting N_HDLC line discipline,” explained Popov.
One might wonder why users should worry about it. Steven J. Vaughan-Nichols explained, because “it's easy to do, which means it's easy for a local user to exploit. Before poo-pooing this as a non-issue, keep in mind that with hosted and cloud computing, many people have ‘local’ access to Linux servers.”
As always, check your distribution and run updates to patch the flaws.
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
![Learn More](https://www.linux-magazine.com/var/linux_magazin/storage/images/media/linux-magazine-eng-us/images/misc/learn-more/834592-1-eng-US/Learn-More_medium.png)
News
-
NVIDIA Released Driver for Upcoming NVIDIA 560 GPU for Linux
Not only has NVIDIA released the driver for its upcoming CPU series, it's the first release that defaults to using open-source GPU kernel modules.
-
OpenMandriva Lx 24.07 Released
If you’re into rolling release Linux distributions, OpenMandriva ROME has a new snapshot with a new kernel.
-
Kernel 6.10 Available for General Usage
Linus Torvalds has released the 6.10 kernel and it includes significant performance increases for Intel Core hybrid systems and more.
-
TUXEDO Computers Releases InfinityBook Pro 14 Gen9 Laptop
Sporting either AMD or Intel CPUs, the TUXEDO InfinityBook Pro 14 is an extremely compact, lightweight, sturdy powerhouse.
-
Google Extends Support for Linux Kernels Used for Android
Because the LTS Linux kernel releases are so important to Android, Google has decided to extend the support period beyond that offered by the kernel development team.
-
Linux Mint 22 Stable Delayed
If you're anxious about getting your hands on the stable release of Linux Mint 22, it looks as if you're going to have to wait a bit longer.
-
Nitrux 3.5.1 Available for Install
The latest version of the immutable, systemd-free distribution includes an updated kernel and NVIDIA driver.
-
Debian 12.6 Released with Plenty of Bug Fixes and Updates
The sixth update to Debian "Bookworm" is all about security mitigations and making adjustments for some "serious problems."
-
Canonical Offers 12-Year LTS for Open Source Docker Images
Canonical is expanding its LTS offering to reach beyond the DEB packages with a new distro-less Docker image.
-
Plasma Desktop 6.1 Released with Several Enhancements
If you're a fan of Plasma Desktop, you should be excited about this new point release.