bpf: cpumap: Fix memory leak in cpu_map_update_elem

CVE-2023-53441

What is CVE-2023-53441?

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

bpf: cpumap: Fix memory leak in cpu_map_update_elem

Syzkaller reported a memory leak as follows:

BUG: memory leak unreferenced object 0xff110001198ef748 (size 192): comm "syz-executor.3", pid 17672, jiffies 4298118891 (age 9.906s) hex dump (first 32 bytes): 00 00 00 00 4a 19 00 00 80 ad e3 e4 fe ff c0 00 ....J........... 00 b2 d3 0c 01 00 11 ff 28 f5 8e 19 01 00 11 ff ........(....... backtrace: [] __cpu_map_entry_alloc+0xf7/0xb00 [] cpu_map_update_elem+0x2fe/0x3d0 [] bpf_map_update_value.isra.0+0x2bd/0x520 [] map_update_elem+0x4cb/0x720 [] __se_sys_bpf+0x8c3/0xb90 [] do_syscall_64+0x30/0x40 [] entry_SYSCALL_64_after_hwframe+0x61/0xc6

BUG: memory leak unreferenced object 0xff110001198ef528 (size 192): comm "syz-executor.3", pid 17672, jiffies 4298118891 (age 9.906s) hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ backtrace: [] __cpu_map_entry_alloc+0x260/0xb00 [] cpu_map_update_elem+0x2fe/0x3d0 [] bpf_map_update_value.isra.0+0x2bd/0x520 [] map_update_elem+0x4cb/0x720 [] __se_sys_bpf+0x8c3/0xb90 [] do_syscall_64+0x30/0x40 [] entry_SYSCALL_64_after_hwframe+0x61/0xc6

BUG: memory leak unreferenced object 0xff1100010fd93d68 (size 8): comm "syz-executor.3", pid 17672, jiffies 4298118891 (age 9.906s) hex dump (first 8 bytes): 00 00 00 00 00 00 00 00 ........ backtrace: [] kvmalloc_node+0x11e/0x170 [] __cpu_map_entry_alloc+0x2f0/0xb00 [] cpu_map_update_elem+0x2fe/0x3d0 [] bpf_map_update_value.isra.0+0x2bd/0x520 [] map_update_elem+0x4cb/0x720 [] __se_sys_bpf+0x8c3/0xb90 [] do_syscall_64+0x30/0x40 [] entry_SYSCALL_64_after_hwframe+0x61/0xc6

In the cpu_map_update_elem flow, when kthread_stop is called before calling the threadfn of rcpu->kthread, since the KTHREAD_SHOULD_STOP bit of kthread has been set by kthread_stop, the threadfn of rcpu->kthread will never be executed, and rcpu->refcnt will never be 0, which will lead to the allocated rcpu, rcpu->queue and rcpu->queue->queue cannot be released.

Calling kthread_stop before executing kthread's threadfn will return -EINTR. We can complete the release of memory resources in this state.

References