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From: Hou Tao <houtao@huaweicloud.com>
To: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Kumar Kartikeya Dwivedi <memxor@gmail.com>,
	Yonghong Song <yhs@meta.com>, bpf <bpf@vger.kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>, Song Liu <song@kernel.org>,
	Hao Luo <haoluo@google.com>, Yonghong Song <yhs@fb.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	KP Singh <kpsingh@kernel.org>,
	Stanislav Fomichev <sdf@google.com>, Jiri Olsa <jolsa@kernel.org>,
	John Fastabend <john.fastabend@gmail.com>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	rcu@vger.kernel.org, Hou Tao <houtao1@huawei.com>,
	Martin KaFai Lau <martin.lau@kernel.org>
Subject: Re: [RFC PATCH bpf-next 0/6] bpf: Handle reuse in bpf memory alloc
Date: Thu, 16 Feb 2023 16:18:55 +0800	[thread overview]
Message-ID: <8d1d1952-e710-004d-dcda-1e8199260180@huaweicloud.com> (raw)
In-Reply-To: <1232a3da-a58f-8cfb-b881-c049abadc203@linux.dev>

Hi,

On 2/16/2023 3:47 PM, Martin KaFai Lau wrote:
> On 2/15/23 6:11 PM, Hou Tao wrote:
>>>>> For local storage, when its owner (sk/task/inode/cgrp) is going away, the
>>>>> memory can be reused immediately. No rcu gp is needed.
>>>> Now it seems it will wait for RCU GP and i think it is still necessary,
>>>> because
>>>> when the process exits, other processes may still access the local storage
>>>> through pidfd or task_struct of the exited process.
>>> When its owner (sk/task/cgrp...) is going away, its owner has reached refcnt 0
>>> and will be kfree immediately next. eg. bpf_sk_storage_free is called just
>>> before the sk is about to be kfree. No bpf prog should have a hold on this sk.
>>> The same should go for the task.
>> A bpf syscall may have already found the task local storage through a pidfd,
>> then the target task exits and the local storage is free immediately, then bpf
>> syscall starts to copy the local storage and there will be a UAF, right ? Did I
>> missing something here ?
> bpf syscall like bpf_pid_task_storage_lookup_elem and you meant
> __put_task_struct() will be called while the syscall's bpf_map_copy_value() is
> still under rcu_read_lock()?
Yes, but I known it is impossible here. I missed that task_struct is released
through call_rcu(), so the calling of __put_task_struct() must happen after the
completion of bpf_map_copy_value() in bpf syscall. Thanks for the explanation.


  reply	other threads:[~2023-02-16  8:19 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-30  4:11 [RFC PATCH bpf-next 0/6] bpf: Handle reuse in bpf memory alloc Hou Tao
2022-12-30  4:11 ` [RFC PATCH bpf-next 1/6] bpf: Support ctor in bpf memory allocator Hou Tao
2022-12-30  4:11 ` [RFC PATCH bpf-next 2/6] bpf: Factor out a common helper free_llist() Hou Tao
2022-12-30  4:11 ` [RFC PATCH bpf-next 3/6] bpf: Pass bitwise flags to bpf_mem_alloc_init() Hou Tao
2022-12-30  4:11 ` [RFC PATCH bpf-next 4/6] bpf: Introduce BPF_MA_NO_REUSE for bpf memory allocator Hou Tao
2022-12-30  4:11 ` [RFC PATCH bpf-next 5/6] bpf: Use BPF_MA_NO_REUSE in htab map Hou Tao
2022-12-30  4:11 ` [RFC PATCH bpf-next 6/6] selftests/bpf: Add test case for element reuse " Hou Tao
2023-01-01  1:26 ` [RFC PATCH bpf-next 0/6] bpf: Handle reuse in bpf memory alloc Alexei Starovoitov
2023-01-01 18:48   ` Yonghong Song
2023-01-03 13:47     ` Hou Tao
2023-01-04  6:10       ` Yonghong Song
2023-01-04  6:30         ` Hou Tao
2023-01-04  7:14           ` Yonghong Song
2023-01-04 18:26             ` Alexei Starovoitov
2023-02-10 16:32               ` Kumar Kartikeya Dwivedi
2023-02-10 21:06                 ` Alexei Starovoitov
2023-02-11  1:09                   ` Hou Tao
2023-02-11 16:33                     ` Alexei Starovoitov
2023-02-11 16:34                       ` Alexei Starovoitov
2023-02-15  1:54                         ` Martin KaFai Lau
2023-02-15  4:02                           ` Hou Tao
2023-02-15  7:22                             ` Martin KaFai Lau
2023-02-16  2:11                               ` Hou Tao
2023-02-16  7:47                                 ` Martin KaFai Lau
2023-02-16  8:18                                   ` Hou Tao [this message]
2023-02-16 13:55                         ` Hou Tao
2023-02-16 16:35                           ` Alexei Starovoitov
2023-02-17  1:19                             ` Hou Tao
2023-02-22 19:30                               ` Alexei Starovoitov
2023-02-15  2:35                       ` Hou Tao
2023-02-15  2:42                         ` Alexei Starovoitov
2023-02-15  3:00                           ` Hou Tao
2023-01-03 13:40   ` Hou Tao
2023-01-03 19:38     ` Alexei Starovoitov
2023-01-10  6:26       ` Martin KaFai Lau

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