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From: Yonghong Song <yhs@fb.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>, <x86@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	<linux-parisc@vger.kernel.org>, <linux-um@lists.infradead.org>,
	<netdev@vger.kernel.org>, <bpf@vger.kernel.org>,
	<linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 12/23] bpf: handle the compat string in bpf_trace_copy_string better
Date: Thu, 28 May 2020 10:06:17 -0700
Message-ID: <a1aa26f4-8c0a-5f8a-8460-6d61f167702d@fb.com> (raw)
In-Reply-To: <20200528043957.GA28494@lst.de>



On 5/27/20 9:39 PM, Christoph Hellwig wrote:
> On Wed, May 27, 2020 at 07:26:30PM -0700, Yonghong Song wrote:
>>> --- a/kernel/trace/bpf_trace.c~xxx
>>> +++ a/kernel/trace/bpf_trace.c
>>> @@ -588,15 +588,22 @@ BPF_CALL_5(bpf_seq_printf, struct seq_fi
>>>    		}
>>>      		if (fmt[i] == 's') {
>>> +			void *unsafe_ptr;
>>> +
>>>    			/* try our best to copy */
>>>    			if (memcpy_cnt >= MAX_SEQ_PRINTF_MAX_MEMCPY) {
>>>    				err = -E2BIG;
>>>    				goto out;
>>>    			}
>>>    -			err = strncpy_from_unsafe(bufs->buf[memcpy_cnt],
>>> -						  (void *) (long) args[fmt_cnt],
>>> -						  MAX_SEQ_PRINTF_STR_LEN);
>>> +			unsafe_ptr = (void *)(long)args[fmt_cnt];
>>> +			if ((unsigned long)unsafe_ptr < TASK_SIZE) {
>>> +				err = strncpy_from_user_nofault(
>>> +					bufs->buf[memcpy_cnt], unsafe_ptr,
>>> +					MAX_SEQ_PRINTF_STR_LEN);
>>> +			} else {
>>> +				err = -EFAULT;
>>> +			}
>>
>> This probably not right.
>> The pointer stored at args[fmt_cnt] is a kernel pointer,
>> but it could be an invalid address and we do not want to fault.
>> Not sure whether it exists or not, we should use
>> strncpy_from_kernel_nofault()?
> 
> If you know it is a kernel pointer with this series it should be
> strncpy_from_kernel_nofault.  But even before the series it should have
> been strncpy_from_unsafe_strict.

The use of strncpy_from_unsafe() mimics old bpf_trace_printk() 
implementation which just changed to _strict version:
https://lkml.org/lkml/2020/5/18/1309

Agreed that we should change to strncpy_from_unsafe_strict().
I can submit a patch for this.

Thanks!

  reply index

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-21 15:22 clean up and streamline probe_kernel_* and friends v4 Christoph Hellwig
2020-05-21 15:22 ` [PATCH 01/23] maccess: unexport probe_kernel_write and probe_user_write Christoph Hellwig
2020-05-21 15:22 ` [PATCH 02/23] maccess: remove various unused weak aliases Christoph Hellwig
2020-05-21 15:22 ` [PATCH 03/23] maccess: remove duplicate kerneldoc comments Christoph Hellwig
2020-05-21 15:22 ` [PATCH 04/23] maccess: clarify " Christoph Hellwig
2020-05-21 15:22 ` [PATCH 05/23] maccess: update the top of file comment Christoph Hellwig
2020-05-21 15:22 ` [PATCH 06/23] maccess: rename strncpy_from_unsafe_user to strncpy_from_user_nofault Christoph Hellwig
2020-05-21 15:22 ` [PATCH 07/23] maccess: rename strncpy_from_unsafe_strict to strncpy_from_kernel_nofault Christoph Hellwig
2020-05-21 15:22 ` [PATCH 08/23] maccess: rename strnlen_unsafe_user to strnlen_user_nofault Christoph Hellwig
2020-05-21 15:22 ` [PATCH 09/23] maccess: remove probe_read_common and probe_write_common Christoph Hellwig
2020-05-21 15:22 ` [PATCH 10/23] maccess: unify the probe kernel arch hooks Christoph Hellwig
2020-05-28  0:55   ` Andrew Morton
2020-05-21 15:22 ` [PATCH 11/23] bpf: factor out a bpf_trace_copy_string helper Christoph Hellwig
2020-05-21 22:10   ` Andrii Nakryiko
2020-05-21 15:22 ` [PATCH 12/23] bpf: handle the compat string in bpf_trace_copy_string better Christoph Hellwig
2020-05-21 22:10   ` Andrii Nakryiko
2020-05-28  2:04   ` Andrew Morton
2020-05-28  2:26     ` Yonghong Song
2020-05-28  4:39       ` Christoph Hellwig
2020-05-28 17:06         ` Yonghong Song [this message]
2020-05-21 15:22 ` [PATCH 13/23] bpf: rework the compat kernel probe handling Christoph Hellwig
2020-05-21 22:10   ` Andrii Nakryiko
2020-05-21 15:22 ` [PATCH 14/23] tracing/kprobes: handle mixed kernel/userspace probes better Christoph Hellwig
2020-05-22  0:04   ` Masami Hiramatsu
2020-05-21 15:22 ` [PATCH 15/23] maccess: remove strncpy_from_unsafe Christoph Hellwig
2020-05-21 15:22 ` [PATCH 16/23] maccess: always use strict semantics for probe_kernel_read Christoph Hellwig
2020-05-21 15:22 ` [PATCH 17/23] maccess: move user access routines together Christoph Hellwig
2020-05-21 15:22 ` [PATCH 18/23] maccess: allow architectures to provide kernel probing directly Christoph Hellwig
2020-05-21 15:22 ` [PATCH 19/23] x86: use non-set_fs based maccess routines Christoph Hellwig
2020-05-21 15:22 ` [PATCH 20/23] maccess: rename probe_kernel_{read,write} to copy_{from,to}_kernel_nofault Christoph Hellwig
2020-05-21 15:22 ` [PATCH 21/23] maccess: rename probe_user_{read,write} to copy_{from,to}_user_nofault Christoph Hellwig
2020-05-21 15:23 ` [PATCH 22/23] maccess: rename probe_kernel_address to get_kernel_nofault Christoph Hellwig
2020-05-21 15:23 ` [PATCH 23/23] maccess: return -ERANGE when copy_from_kernel_nofault_allowed fails Christoph Hellwig
2020-05-21 18:03 ` clean up and streamline probe_kernel_* and friends v4 Linus Torvalds
2020-05-22  0:22 ` Masami Hiramatsu
2020-05-25 22:19 ` Andrew Morton
2020-05-26  6:13   ` Christoph Hellwig
2020-05-28  0:36     ` Andrew Morton

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