linux-kernel - Re: [PATCH net 2/3] bpf: fix splat for illegal devmap percpu allocation

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Date:   Tue, 17 Oct 2017 08:54:13 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     davem@...emloft.net, tj@...nel.org, ast@...nel.org,
        john.fastabend@...il.com, mark.rutland@....com, richard@....at,
        sp3485@...umbia.edu, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 2/3] bpf: fix splat for illegal devmap percpu
 allocation

On Tue, Oct 17, 2017 at 04:55:53PM +0200, Daniel Borkmann wrote:
> It was reported that syzkaller was able to trigger a splat on
> devmap percpu allocation due to illegal/unsupported allocation
> request size passed to __alloc_percpu():
> 
>   [   70.094249] illegal size (32776) or align (8) for percpu allocation
>   [   70.094256] ------------[ cut here ]------------
>   [   70.094259] WARNING: CPU: 3 PID: 3451 at mm/percpu.c:1365 pcpu_alloc+0x96/0x630
>   [...]
>   [   70.094325] Call Trace:
>   [   70.094328]  __alloc_percpu_gfp+0x12/0x20
>   [   70.094330]  dev_map_alloc+0x134/0x1e0
>   [   70.094331]  SyS_bpf+0x9bc/0x1610
>   [   70.094333]  ? selinux_task_setrlimit+0x5a/0x60
>   [   70.094334]  ? security_task_setrlimit+0x43/0x60
>   [   70.094336]  entry_SYSCALL_64_fastpath+0x1a/0xa5
> 
> This was due to too large max_entries for the map such that we
> surpassed the upper limit of PCPU_MIN_UNIT_SIZE. It's fine to
> fail naturally here, so switch to __alloc_percpu_gfp() and pass
> __GFP_NOWARN instead.
> 
> Fixes: 11393cc9b9be ("xdp: Add batching support to redirect map")
> Reported-by: Mark Rutland <mark.rutland@....com>
> Reported-by: Shankara Pailoor <sp3485@...umbia.edu>
> Reported-by: Richard Weinberger <richard@....at>
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> Cc: John Fastabend <john.fastabend@...il.com>

Acked-by: Alexei Starovoitov <ast@...nel.org>