netdev - Re: Possible kernel memory leak in bpf

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Date: Sun, 8 Oct 2023 10:46:00 +0800
From: Hou Tao <houtao@...weicloud.com>
To: Hsin-Wei Hung <hsinweih@....edu>
Cc: Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
 Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
 Yonghong Song <yhs@...com>, John Fastabend <john.fastabend@...il.com>,
 KP Singh <kpsingh@...nel.org>, Network Development <netdev@...r.kernel.org>,
 bpf <bpf@...r.kernel.org>, Kumar Kartikeya Dwivedi <memxor@...il.com>
Subject: Re: Possible kernel memory leak in bpf_timer

Hi,

On 9/27/2023 1:32 PM, Hsin-Wei Hung wrote:
> Hi,
>
> We found a potential memory leak in bpf_timer in v5.15.26 using a
> customized syzkaller for fuzzing bpf runtime. It can happen when
> an arraymap is being released. An entry that has been checked by
> bpf_timer_cancel_and_free() can again be initialized by bpf_timer_init().
> Since both paths are almost identical between v5.15 and net-next,
> I suspect this problem still exists. Below are kmemleak report and
> some additional printks I inserted.
>
> [ 1364.081694] array_map_free_timers map:0xffffc900005a9000
> [ 1364.081730] ____bpf_timer_init map:0xffffc900005a9000
> timer:0xffff888001ab4080
>
> *no bpf_timer_cancel_and_free that will kfree struct bpf_hrtimer*
> at 0xffff888001ab4080 is called

I think the kmemleak happened as follows:

bpf_timer_init()
  lock timer->lock
    read timer->timer as NULL
    read map->usercnt != 0

                bpf_map_put_uref()
                  // map->usercnt = 0
                  atomic_dec_and_test(map->usercnt)
                    array_map_free_timers()
                    // just return and lead to mem leak
                    find timer->timer is NULL

    t = bpf_map_kmalloc_node()
    timer->timer = t
  unlock timer->lock

Could you please try the attached patch to check whether the kmemleak
problem has been fixed ?

>
> [ 1383.907869] kmemleak: 1 new suspected memory leaks (see
> /sys/kernel/debug/kmemleak)
> BUG: memory leak
> unreferenced object 0xffff888001ab4080 (size 96):
>   comm "sshd", pid 279, jiffies 4295233126 (age 29.952s)
>   hex dump (first 32 bytes):
>     80 40 ab 01 80 88 ff ff 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:
>     [<000000009d018da0>] bpf_map_kmalloc_node+0x89/0x1a0
>     [<00000000ebcb33fc>] bpf_timer_init+0x177/0x320
>     [<00000000fb7e90bf>] 0xffffffffc02a0358
>     [<000000000c89ec4f>] __cgroup_bpf_run_filter_skb+0xcbf/0x1110
>     [<00000000fd663fc0>] ip_finish_output+0x13d/0x1f0
>     [<00000000acb3205c>] ip_output+0x19b/0x310
>     [<000000006b584375>] __ip_queue_xmit+0x182e/0x1ed0
>     [<00000000b921b07e>] __tcp_transmit_skb+0x2b65/0x37f0
>     [<0000000026104b23>] tcp_write_xmit+0xf19/0x6290
>     [<000000006dc71bc5>] __tcp_push_pending_frames+0xaf/0x390
>     [<00000000251b364a>] tcp_push+0x452/0x6d0
>     [<000000008522b7d3>] tcp_sendmsg_locked+0x2567/0x3030
>     [<0000000038c644d2>] tcp_sendmsg+0x30/0x50
>     [<000000009fe3413f>] inet_sendmsg+0xba/0x140
>     [<0000000034d78039>] sock_sendmsg+0x13d/0x190
>     [<00000000f55b8db6>] sock_write_iter+0x296/0x3d0
>
>
> Thanks,
> Hsin-Wei (Amery)
>
>
> .


View attachment "0001-bpf-Check-map-usercnt-again-after-timer-timer-is-ass.patch" of type "text/plain" (1014 bytes)