The recently discovered CVE-2023-0459 is a critical vulnerability associated with the 'copy_from_user()' function in 64-bit versions of the Linux kernel. If exploited, this vulnerability could allow an attacker to leak sensitive information from the kernel memory. In this post, we will discuss the exploit details, code snippets, and links to original references that are relevant to CVE-2023-0459.

Background: copy_from_user() and access_ok

The copy_from_user() function performs data copying from a user-space process to the kernel memory. This copy is strictly controlled by access_ok checks to ensure that information leaks do not occur due to the differences between user and kernel addresses.

The Issue

The vulnerability in the 64-bit Linux kernel lies in the '__uaccess_begin_nospec' function. The incorrect implementation of this function leads to a bypass of the 'access_ok' check, allowing an attacker to pass a kernel pointer to copy_from_user(). Consequently, this would enable an attacker to leak sensitive information.

Exploit Details

The attacker can exploit this vulnerability by crafting a malicious user-space process that leverages the '__uaccess_begin_nospec' function to bypass the 'access_ok' check. In doing so, they can provide a kernel pointer as the address in copy_from_user().

The following code snippet demonstrates how the __uaccess_begin_nospec is implemented

#ifndef CONFIG_UACCESS_BEGIN_NOSPEC
#define __uaccess_begin_nospec()	\
({	\
	barrier_nospec();	\
	__uaccess_enable();	\
})
#define __uaccess_end_nospec()	\
({	\
	__uaccess_disable();	\
	barrier_nospec();	\
})
#endif

The improper implementation bypasses the access_ok check in the Linux kernel memory, allowing a kernel pointer to be passed to copy_from_user().

References and Further Reading

1. The Linux Kernel 5.16.x < 5.16-rc4 Access Kernel Memory Disclosure vulnerability is discussed in detail here: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-0459
2. The Linux kernel commit introducing the flaw can be found at https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=74e19efff8061ef55957c3abd71614eff42f47
3. Linux kernel source code: https://github.com/torvalds/linux

Recommendations

To mitigate the CVE-2023-0459 vulnerability, we strongly recommend upgrading the Linux kernel beyond the commit 74e19efff8061ef55957c3abd71614eff42f47. This will ensure that the __uaccess_begin_nospec is correctly implemented, effectively securing the 'copy_from_user()' function and preventing potential information leaks.

Conclusion

Given the serious potential for information leaks due to CVE-2023-0459, it is essential for users and administrators to promptly update their Linux kernel versions to safeguard their systems against attackers. Staying informed and proactive about security vulnerabilities is the key to ensuring the continued protection of sensitive data in our increasingly digital world.

Timeline

Published on: 05/25/2023 14:15:00 UTC
Last modified on: 06/01/2023 16:45:00 UTC