CVE-2024-56642

In the Linux kernel, the following vulnerability has been resolved:

tipc: Fix use-after-free of kernel socket in cleanup_bearer().

syzkaller reported a use-after-free of UDP kernel socket in cleanup_bearer() without repro. [0][1]

When bearer_disable() calls tipc_udp_disable(), cleanup of the UDP kernel socket is deferred by work calling cleanup_bearer().

tipc_exit_net() waits for such works to finish by checking tipc_net(net)->wq_count. However, the work decrements the count too early before releasing the kernel socket, unblocking cleanup_net() and resulting in use-after-free.

Lets move the decrement after releasing the socket in cleanup_bearer().

[0]: ref_tracker: net notrefcnt@000000009b3d1faf has 1/1 users at sk_alloc+0x438/0x608 inet_create+0x4c8/0xcb0 __sock_create+0x350/0x6b8 sock_create_kern+0x58/0x78 udp_sock_create4+0x68/0x398 udp_sock_create+0x88/0xc8 tipc_udp_enable+0x5e8/0x848 __tipc_nl_bearer_enable+0x84c/0xed8 tipc_nl_bearer_enable+0x38/0x60 genl_family_rcv_msg_doit+0x170/0x248 genl_rcv_msg+0x400/0x5b0 netlink_rcv_skb+0x1dc/0x398 genl_rcv+0x44/0x68 netlink_unicast+0x678/0x8b0 netlink_sendmsg+0x5e4/0x898 ____sys_sendmsg+0x500/0x830

[1]: BUG: KMSAN: use-after-free in udp_hashslot include/net/udp.h:85 [inline] BUG: KMSAN: use-after-free in udp_lib_unhash+0x3b8/0x930 net/ipv4/udp.c:1979 udp_hashslot include/net/udp.h:85 [inline] udp_lib_unhash+0x3b8/0x930 net/ipv4/udp.c:1979 sk_common_release+0xaf/0x3f0 net/core/sock.c:3820 inet_release+0x1e0/0x260 net/ipv4/af_inet.c:437 inet6_release+0x6f/0xd0 net/ipv6/af_inet6.c:489 __sock_release net/socket.c:658 [inline] sock_release+0xa0/0x210 net/socket.c:686 cleanup_bearer+0x42d/0x4c0 net/tipc/udp_media.c:819 process_one_work kernel/workqueue.c:3229 [inline] process_scheduled_works+0xcaf/0x1c90 kernel/workqueue.c:3310 worker_thread+0xf6c/0x1510 kernel/workqueue.c:3391 kthread+0x531/0x6b0 kernel/kthread.c:389 ret_from_fork+0x60/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:244

Uninit was created at: slab_free_hook mm/slub.c:2269 [inline] slab_free mm/slub.c:4580 [inline] kmem_cache_free+0x207/0xc40 mm/slub.c:4682 net_free net/core/net_namespace.c:454 [inline] cleanup_net+0x16f2/0x19d0 net/core/net_namespace.c:647 process_one_work kernel/workqueue.c:3229 [inline] process_scheduled_works+0xcaf/0x1c90 kernel/workqueue.c:3310 worker_thread+0xf6c/0x1510 kernel/workqueue.c:3391 kthread+0x531/0x6b0 kernel/kthread.c:389 ret_from_fork+0x60/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:244

CPU: 0 UID: 0 PID: 54 Comm: kworker/0:2 Not tainted 6.12.0-rc1-00131-gf66ebf37d69c #7 91723d6f74857f70725e1583cba3cf4adc716cfa Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 Workqueue: events cleanup_bearer

Weakness

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Potential Mitigations

References

• https://git.kernel.org/stable/c/4e69457f9dfae67435f3ccf29008768eae860415
• https://git.kernel.org/stable/c/650ee9a22d7a2de8999fac2d45983597a0c22359
• https://git.kernel.org/stable/c/6a2fa13312e51a621f652d522d7e2df7066330b6
• https://git.kernel.org/stable/c/d00d4470bf8c4282617a3a10e76b20a9c7e4cffa
• https://git.kernel.org/stable/c/d2a4894f238551eae178904e7f45af87577074fd
• https://git.kernel.org/stable/c/d62d5180c036eeac09f80660edc7a602b369125f
• https://git.kernel.org/stable/c/e48b211c4c59062cb6dd6c2c37c51a7cc235a464