The recent discovery of a NULL pointer dereference vulnerability (CVE-2023-0394) within the Linux kernel has raised significant concerns since it could lead to system crashes. This long-read post is intended to provide an in-depth discussion of this vulnerability, starting with an overview of the affected component, followed by details about the flaw, and concluding with an examination of the exploit, code snippets, and original references.
Affected Component: Rawv6 Network Subcomponent
The vulnerability specifically impacts the rawv6 network subcomponent of the Linux kernel, which is responsible for handling raw IPv6 packets. The affected function, called rawv6_push_pending_frames, is located in the file net/ipv6/raw.c within the Linux kernel source code. This function plays a crucial role in transferring and handling raw IPv6 packets between the different layers of the kernel's networking stack.
The Flaw: NULL Pointer Dereference
A NULL pointer dereference is a type of programming error that occurs when a program tries to access memory or call functions through a pointer that has not been properly initialized or has been set to NULL. In the case of CVE-2023-0394, this error occurs because the rawv6_push_pending_frames function does not verify whether a specific pointer is NULL before attempting to use it.
The problematic code snippet can be found in the rawv6_push_pending_frames function within the net/ipv6/raw.c file:
struct ipv6hdr *hdr;
struct sock *sk;
// ...
hdr = rawv6_hdr(skb);
In the code above, rawv6_hdr(skb) may return a NULL pointer, but there is no check to ensure the "hdr" pointer is valid before it gets dereferenced later in the function. Here's the problematic portion of the code:
if (opt->srcrt) {
struct ipv6_rt_hdr *rthdr;
// ...
opt_clone = ipv6_dup_options(skb, opt);
// ...
rthdr = (struct ipv6_rt_hdr *)__skb_pull(skb, prevhdr_len);
// ...
rthdr->nxt = prevhdr;
// ...
}
In this part of the function, rthdr is set to a memory location within the skb networking buffer, which is determined by the return value of the __skb_pull(skb, prevhdr_len) function. However, if the pointer "hdr" was NULL, then the skb_pull function will return an incorrect memory location, and dereferencing rthdr will lead to a NULL pointer dereference, potentially causing a system crash.
Exploit Details
The exploit for CVE-2023-0394 could be used by an attacker to cause a denial of service (DoS) by sending a specially crafted IPv6 packet to a device running a vulnerable version of the Linux kernel. This would trigger the NULL pointer dereference within the rawv6_push_pending_frames function, causing the kernel to crash and the system to become unresponsive.
Original References
For more information on this vulnerability, its discovery, and its potential impact on the Linux kernel, consult the following references:
- CVE-2023-0394: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-0394
- Linux Kernel Source Code: https://elixir.bootlin.com/linux/v5.9/source/net/ipv6/raw.c#L533
- Linux Kernel Mailing List Patch Submission: https://lkml.org/lkml/2023/3/10/439
Conclusion
CVE-2023-0394 highlights the importance of meticulous code reviewing and testing of critical components within the Linux kernel. The NULL pointer dereference flaw in the rawv6_push_pending_frames function is a serious vulnerability that could lead to system crashes and potential denial-of-service attacks. By understanding the nature of this flaw and how it can be triggered, developers and system administrators can take appropriate steps to mitigate the risks associated with the vulnerability.
Timeline
Published on: 01/26/2023 21:18:00 UTC
Last modified on: 03/03/2023 01:15:00 UTC