netdev - Possible kernel memory leak in bpf

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Date: Tue, 26 Sep 2023 22:32:07 -0700
From: Hsin-Wei Hung <hsinweih@....edu>
To: 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>
Subject: Possible kernel memory leak in bpf_timer

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

[ 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)