CVE-2024-44934 in Linux
Summary
by MITRE • 08/26/2024
In the Linux kernel, the following vulnerability has been resolved:
net: bridge: mcast: wait for previous gc cycles when removing port
syzbot hit a use-after-free[1] which is caused because the bridge doesn't
make sure that all previous garbage has been collected when removing a port. What happens is: CPU 1 CPU 2 start gc cycle remove port acquire gc lock first wait for lock call br_multicasg_gc() directly acquire lock now but free port the port can be freed while grp timers still running
Make sure all previous gc cycles have finished by using flush_work before freeing the port.
[1]
BUG: KASAN: slab-use-after-free in br_multicast_port_group_expired+0x4c0/0x550 net/bridge/br_multicast.c:861 Read of size 8 at addr ffff888071d6d000 by task syz.5.1232/9699
CPU: 1 PID: 9699 Comm: syz.5.1232 Not tainted 6.10.0-rc5-syzkaller-00021-g24ca36a562d6 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024 Call Trace: __dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:114 print_address_description mm/kasan/report.c:377 [inline]
print_report+0xc3/0x620 mm/kasan/report.c:488 kasan_report+0xd9/0x110 mm/kasan/report.c:601 br_multicast_port_group_expired+0x4c0/0x550 net/bridge/br_multicast.c:861 call_timer_fn+0x1a3/0x610 kernel/time/timer.c:1792 expire_timers kernel/time/timer.c:1843 [inline]
__run_timers+0x74b/0xaf0 kernel/time/timer.c:2417 __run_timer_base kernel/time/timer.c:2428 [inline]
__run_timer_base kernel/time/timer.c:2421 [inline]
run_timer_base+0x111/0x190 kernel/time/timer.c:2437
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Analysis
by VulDB Data Team • 10/13/2024
The vulnerability identified as CVE-2024-44934 resides within the Linux kernel's networking subsystem, specifically within the bridge multicast implementation. This issue manifests as a use-after-free condition that occurs during the removal of network bridge ports. The flaw stems from inadequate synchronization mechanisms that fail to ensure all ongoing garbage collection cycles complete before a port is freed, creating a race condition between concurrent CPU operations. The vulnerability was discovered through systematic fuzzing by syzbot, which revealed a critical memory safety issue in the multicast bridge functionality.
The technical root cause involves a race condition between two distinct execution paths within the kernel's bridge multicast subsystem. When a port removal operation occurs, the system attempts to acquire a garbage collection lock before proceeding with the cleanup process. However, the existing code structure allows for a scenario where the garbage collection cycle is initiated on one CPU while the port removal is processed on another. The port can be freed while multicast group timers are still active, leading to memory access violations when these timers attempt to reference deallocated memory structures. This particular use-after-free vulnerability maps directly to CWE-416, which defines the improper release of memory resources, and represents a classic example of concurrent access violations in kernel space.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially enabling arbitrary code execution or system instability. An attacker could exploit this condition to cause kernel crashes through null pointer dereferences or more sophisticated attacks that leverage the freed memory for privilege escalation. The vulnerability affects systems running Linux kernel versions where the multicast bridge functionality is active, particularly those utilizing network bridging for virtualized environments or complex network topologies. This flaw poses significant risk in cloud computing environments where bridge networking is commonly employed for container networking or virtual machine interconnectivity.
Mitigation strategies should focus on ensuring proper synchronization before port cleanup operations. The recommended fix involves implementing flush_work calls before port destruction to guarantee all pending garbage collection work items have completed execution. This approach aligns with standard kernel development practices for managing workqueue operations and prevents the race condition by ensuring memory safety before resource deallocation. System administrators should prioritize applying the relevant kernel patches that implement this fix, particularly in production environments where bridge networking is actively utilized. The vulnerability demonstrates the critical importance of proper kernel synchronization mechanisms and highlights how seemingly simple race conditions can lead to severe security implications in kernel space operations, making it essential for organizations to maintain up-to-date kernel versions and monitor for similar vulnerabilities through systematic security auditing.