In the world of Linux, it is crucial to maintain a secure and stable operating system. One significant aspect of ensuring this is taking care of any vulnerabilities that may arise. In recent times, a vulnerability was identified and resolved within the Linux kernel's bpf subsystem that could cause memory leaks. This post will discuss the details of this vulnerability, the resolution, and provide some code snippets and references for further understanding.
The vulnerability we're discussing today is related to the Linux kernel's bpf (Berkeley Packet Filter) subsystem, specifically, the bpf_sk_select_reuseport() function. It has been assigned the identifier CVE-2025-21683. The original reference highlighting the issue can be found here.
The bpf_sk_select_reuseport() function is a part of the bpf subsystem's implementation for the userspace API, providing an efficient and flexible way to filter network packets. However, it was observed that when looking up a socket in the sockmap, it could return a TCP ESTABLISHED socket even when the socket had SO_ATTACH_REUSEPORT_EBPF set before it was established. In simpler terms, a non-refcounted socket could be left with a non-NULL sk_reuseport_cb field.
Therefore, this resulted in a memory leak, causing significant issues for Linux systems. To fix this vulnerability, the kernel developers dropped the sk reference in both error paths, effectively resolving the problem.
Here's a snippet of the code fix
unreferenced object xffff888101911800 (size 2048):
comm "test_progs", pid 44109, jiffies 4297131437
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
80 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace (crc 9336483b):
__kmalloc_noprof+x3bf/x560
__reuseport_alloc+x1d/x40
reuseport_alloc+xca/x150
reuseport_attach_prog+x87/x140
sk_reuseport_attach_bpf+xc8/x100
sk_setsockopt+x1181/x199
do_sock_setsockopt+x12b/x160
__sys_setsockopt+x7b/xc
__x64_sys_setsockopt+x1b/x30
do_syscall_64+x93/x180
entry_SYSCALL_64_after_hwframe+x76/x7e
With the memory leak now resolved, the potential for any negative impact from this vulnerability has been reduced drastically. By dropping the sk reference, the Linux kernel is now more secure and stable.
In conclusion, this post covered the details of the CVE-2025-21683 vulnerability found in the Linux kernel's bpf subsystem. We have presented the original references regarding the issue, as well as the code snippet showcasing the fix applied. The hard work of kernel developers worldwide ensures that the Linux ecosystem remains secure and functional for users everywhere. Always remember to update your Linux systems regularly to stay protected against such vulnerabilities!
Timeline
Published on: 01/31/2025 12:15:29 UTC
Last modified on: 02/03/2025 20:01:29 UTC