CVE-2024-26731 in Linux
Summary
by MITRE • 04/03/2024
In the Linux kernel, the following vulnerability has been resolved:
bpf, sockmap: Fix NULL pointer dereference in sk_psock_verdict_data_ready()
syzbot reported the following NULL pointer dereference issue [1]:
BUG: kernel NULL pointer dereference, address: 0000000000000000 [...]
RIP: 0010:0x0 [...]
Call Trace: sk_psock_verdict_data_ready+0x232/0x340 net/core/skmsg.c:1230 unix_stream_sendmsg+0x9b4/0x1230 net/unix/af_unix.c:2293 sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg+0x221/0x270 net/socket.c:745 ____sys_sendmsg+0x525/0x7d0 net/socket.c:2584 ___sys_sendmsg net/socket.c:2638 [inline]
__sys_sendmsg+0x2b0/0x3a0 net/socket.c:2667 do_syscall_64+0xf9/0x240 entry_SYSCALL_64_after_hwframe+0x6f/0x77
If sk_psock_verdict_data_ready() and sk_psock_stop_verdict() are called concurrently, psock->saved_data_ready can be NULL, causing the above issue.
This patch fixes this issue by calling the appropriate data ready function using the sk_psock_data_ready() helper and protecting it from concurrency with sk->sk_callback_lock.
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Analysis
by VulDB Data Team • 08/03/2025
The vulnerability identified as CVE-2024-26731 represents a critical NULL pointer dereference flaw within the Linux kernel's BPF (Berkeley Packet Filter) subsystem, specifically affecting the sockmap functionality. This issue manifests in the sk_psock_verdict_data_ready() function located in the net/core/skmsg.c file, where concurrent execution paths can lead to a race condition that results in kernel memory corruption. The vulnerability was discovered through automated fuzzing by syzbot, which identified the problematic execution path that leads to a kernel NULL pointer dereference at address zero, indicating a severe memory management failure that could potentially lead to system crashes or privilege escalation.
The technical root cause of this vulnerability stems from improper synchronization mechanisms within the socket processing code. When the sk_psock_verdict_data_ready() function executes concurrently with sk_psock_stop_verdict(), the psock->saved_data_ready pointer can become NULL during the transition period. This race condition occurs because the function attempts to invoke a callback that has already been cleared by the stop operation, creating a situation where the kernel tries to execute code at a NULL memory address. The call stack shows this issue originates from unix_stream_sendmsg processing, which eventually calls the problematic function through a chain of socket operations that include net/unix/af_unix.c and net/socket.c components.
The operational impact of this vulnerability extends beyond simple system instability, as it represents a potential vector for denial-of-service attacks against kernel space operations. The flaw specifically affects BPF socket map functionality and Unix domain socket communications, which are fundamental components of Linux networking infrastructure. According to CWE-476, this vulnerability maps directly to a NULL pointer dereference condition that can be exploited to crash kernel threads or potentially escalate privileges. The ATT&CK framework categorizes this under T1068, as it represents a privilege escalation opportunity through kernel-level memory corruption, while T1499 covers the potential for system instability and denial-of-service conditions.
Mitigation strategies for this vulnerability should focus on implementing proper locking mechanisms around the affected code paths. The patch addresses the issue by introducing the sk_psock_data_ready() helper function which properly handles the callback invocation while maintaining synchronization through the sk->sk_callback_lock. This approach prevents concurrent access to the saved_data_ready pointer and ensures that any callback invocation occurs only when valid. System administrators should prioritize applying the kernel patch immediately, particularly in environments where BPF socket maps are actively used or where Unix domain socket communications are prevalent. Additionally, monitoring for unusual system behavior or kernel oops messages can help detect potential exploitation attempts, while implementing proper kernel version management ensures all systems remain protected against this specific race condition vulnerability.