netdev - RE: [Patch bpf-next] bpf: clear per_cpu pointers in bpf_prog_clone

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Date:   Wed, 17 Feb 2021 13:33:44 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
        Jiang Wang <jiang.wang@...edance.com>,
        Alexei Starovoitov <ast@...nel.org>
Subject: RE: [Patch bpf-next] bpf: clear per_cpu pointers in
 bpf_prog_clone_create()

Cong Wang wrote:
> From: Cong Wang <cong.wang@...edance.com>
> 
> Pretty much similar to commit 1336c662474e
> ("bpf: Clear per_cpu pointers during bpf_prog_realloc") we also need to
> clear these two percpu pointers in bpf_prog_clone_create(), otherwise
> would get a double free:
> 
>  BUG: kernel NULL pointer dereference, address: 0000000000000000
>  #PF: supervisor read access in kernel mode
>  #PF: error_code(0x0000) - not-present page
>  PGD 0 P4D 0
>  Oops: 0000 [#1] SMP PTI
>  CPU: 13 PID: 8140 Comm: kworker/13:247 Kdump: loaded Tainted: G                W    OE
>   5.11.0-rc4.bm.1-amd64+ #1
>  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
>  test_bpf: #1 TXA
>  Workqueue: events bpf_prog_free_deferred
>  RIP: 0010:percpu_ref_get_many.constprop.97+0x42/0xf0
>  Code: [...]
>  RSP: 0018:ffffa6bce1f9bda0 EFLAGS: 00010002
>  RAX: 0000000000000001 RBX: 0000000000000000 RCX: 00000000021dfc7b
>  RDX: ffffffffae2eeb90 RSI: 867f92637e338da5 RDI: 0000000000000046
>  RBP: ffffa6bce1f9bda8 R08: 0000000000000000 R09: 0000000000000001
>  R10: 0000000000000046 R11: 0000000000000000 R12: 0000000000000280
>  R13: 0000000000000000 R14: 0000000000000000 R15: ffff9b5f3ffdedc0
>  FS:    0000000000000000(0000) GS:ffff9b5f2fb40000(0000) knlGS:0000000000000000
>  CS:    0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 0000000000000000 CR3: 000000027c36c002 CR4: 00000000003706e0
>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>  Call Trace:
>     refill_obj_stock+0x5e/0xd0
>     free_percpu+0xee/0x550
>     __bpf_prog_free+0x4d/0x60
>     process_one_work+0x26a/0x590
>     worker_thread+0x3c/0x390
>     ? process_one_work+0x590/0x590
>     kthread+0x130/0x150
>     ? kthread_park+0x80/0x80
>     ret_from_fork+0x1f/0x30
> 
> This bug is 100% reproducible with test_kmod.sh.
> 
> Reported-by: Jiang Wang <jiang.wang@...edance.com>
> Fixes: 700d4796ef59 ("bpf: Optimize program stats")
> Fixes: ca06f55b9002 ("bpf: Add per-program recursion prevention mechanism")
> Cc: Alexei Starovoitov <ast@...nel.org>
> Signed-off-by: Cong Wang <cong.wang@...edance.com>
> ---

Acked-by: John Fastabend <john.fastabend@...il.com>