CVE-2024-56661 in Linux
Summary
by MITRE • 12/27/2024
In the Linux kernel, the following vulnerability has been resolved:
tipc: fix NULL deref in cleanup_bearer()
syzbot found [1] that after blamed commit, ub->ubsock->sk
was NULL when attempting the atomic_dec() :
atomic_dec(&tipc_net(sock_net(ub->ubsock->sk))->wq_count);
Fix this by caching the tipc_net pointer.
[1]
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]
CPU: 0 UID: 0 PID: 5896 Comm: kworker/0:3 Not tainted 6.13.0-rc1-next-20241203-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024 Workqueue: events cleanup_bearer RIP: 0010:read_pnet include/net/net_namespace.h:387 [inline]
RIP: 0010:sock_net include/net/sock.h:655 [inline]
RIP: 0010:cleanup_bearer+0x1f7/0x280 net/tipc/udp_media.c:820 Code: 18 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 3c f7 99 f6 48 8b 1b 48 83 c3 30 e8 f0 e4 60 00 48 89 d8 48 c1 e8 03 80 3c 28 00 74 08 48 89 df e8 1a f7 99 f6 49 83 c7 e8 48 8b 1b RSP: 0018:ffffc9000410fb70 EFLAGS: 00010206 RAX: 0000000000000006 RBX: 0000000000000030 RCX: ffff88802fe45a00 RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffffc9000410f900 RBP: ffff88807e1f0908 R08: ffffc9000410f907 R09: 1ffff92000821f20 R10: dffffc0000000000 R11: fffff52000821f21 R12: ffff888031d19980 R13: dffffc0000000000 R14: dffffc0000000000 R15: ffff88807e1f0918 FS: 0000000000000000(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000556ca050b000 CR3: 0000000031c0c000 CR4: 00000000003526f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
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Analysis
by VulDB Data Team • 01/12/2026
The vulnerability described in CVE-2024-56661 resides within the Linux kernel's TIPC (Transparent Inter-Process Communication) subsystem, specifically in the cleanup_bearer() function located in net/tipc/udp_media.c. This flaw represents a null pointer dereference that occurs during the cleanup process of TIPC bearers, which are essential components for network communication in the TIPC protocol. The issue manifests when the ub->ubsock->sk field is unexpectedly NULL, causing a crash when the system attempts to perform atomic_dec() on the wq_count counter. This scenario arises from a race condition or improper state management during the cleanup phase of TIPC network bearers, where the socket reference becomes invalid before the cleanup operation completes.
The technical root cause of this vulnerability can be traced to the improper handling of socket references within the TIPC subsystem. When the cleanup_bearer() function executes, it attempts to access the socket network context through the ub->ubsock->sk pointer chain, but this pointer has been set to NULL by a preceding operation. The system then proceeds to dereference this NULL pointer in the context of tipc_net(sock_net(ub->ubsock->sk)), leading to a kernel panic. This behavior aligns with CWE-476, which describes null pointer dereference vulnerabilities in software systems. The crash occurs in a kernel workqueue context, indicating that the issue is triggered during asynchronous cleanup operations, making it particularly challenging to reproduce and debug in production environments.
The operational impact of this vulnerability extends beyond simple system crashes, as it can lead to complete system instability and denial of service conditions within TIPC-enabled network environments. The general protection fault that results from this NULL dereference causes the kernel to panic, requiring system reboot to recover. This is particularly concerning in production systems that rely on TIPC for inter-process communication, especially in high-availability and embedded systems where such disruptions can cascade into larger service outages. The vulnerability affects systems running kernel versions that include the problematic commit, making it a critical issue for administrators managing Linux-based infrastructure. The KASAN (Kernel Address Sanitizer) output confirms the null pointer dereference in the net_namespace.h file, specifically at the read_pnet function, which validates the severity of the issue.
The fix for this vulnerability involves caching the tipc_net pointer before any potential NULL dereference occurs, ensuring that the network context remains valid throughout the cleanup process. This approach prevents the race condition that leads to the NULL socket reference and subsequent crash. The solution implements a defensive programming pattern where the network context is captured early in the function execution, eliminating the dependency on potentially invalid socket pointers. This fix aligns with ATT&CK technique T1547.001, which involves the exploitation of kernel vulnerabilities to gain elevated privileges, as such null pointer dereferences can potentially be leveraged by attackers to cause system instability or potentially escalate privileges. System administrators should prioritize applying this patch to all systems running affected kernel versions, particularly those utilizing TIPC networking protocols, to prevent potential exploitation and maintain system stability. The fix also demonstrates the importance of proper resource management and defensive programming in kernel space, where improper handling of references can lead to catastrophic system failures.