Re: [PATCH bpf] bpf: cpumap: Fix memory leak in cpu_map_update_elem

[Hou Tao]

On 7/11/2023 7:58 PM, Pu Lehui wrote:
> From: Pu Lehui <pulehui@xxxxxxxxxx>
>
> 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:
>     [<ffffffffadd28087>] __cpu_map_entry_alloc+0xf7/0xb00
>     [<ffffffffadd28d8e>] cpu_map_update_elem+0x2fe/0x3d0
>     [<ffffffffadc6d0fd>] bpf_map_update_value.isra.0+0x2bd/0x520
>     [<ffffffffadc7349b>] map_update_elem+0x4cb/0x720
>     [<ffffffffadc7d983>] __se_sys_bpf+0x8c3/0xb90
>     [<ffffffffb029cc80>] do_syscall_64+0x30/0x40
>     [<ffffffffb0400099>] 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:
>     [<ffffffffadd281f0>] __cpu_map_entry_alloc+0x260/0xb00
>     [<ffffffffadd28d8e>] cpu_map_update_elem+0x2fe/0x3d0
>     [<ffffffffadc6d0fd>] bpf_map_update_value.isra.0+0x2bd/0x520
>     [<ffffffffadc7349b>] map_update_elem+0x4cb/0x720
>     [<ffffffffadc7d983>] __se_sys_bpf+0x8c3/0xb90
>     [<ffffffffb029cc80>] do_syscall_64+0x30/0x40
>     [<ffffffffb0400099>] 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:
>     [<ffffffffade5db3e>] kvmalloc_node+0x11e/0x170
>     [<ffffffffadd28280>] __cpu_map_entry_alloc+0x2f0/0xb00
>     [<ffffffffadd28d8e>] cpu_map_update_elem+0x2fe/0x3d0
>     [<ffffffffadc6d0fd>] bpf_map_update_value.isra.0+0x2bd/0x520
>     [<ffffffffadc7349b>] map_update_elem+0x4cb/0x720
>     [<ffffffffadc7d983>] __se_sys_bpf+0x8c3/0xb90
>     [<ffffffffb029cc80>] do_syscall_64+0x30/0x40
>     [<ffffffffb0400099>] 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.
>
> Fixes: 6710e1126934 ("bpf: introduce new bpf cpu map type BPF_MAP_TYPE_CPUMAP")
> Signed-off-by: Pu Lehui <pulehui@xxxxxxxxxx>

Acked-by: Hou Tao <houtao1@xxxxxxxxxx>