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Thu, 28 May 2020 17:06:20 +0000 Subject: Re: [PATCH 12/23] bpf: handle the compat string in bpf_trace_copy_string better To: Christoph Hellwig CC: Andrew Morton , , Alexei Starovoitov , Daniel Borkmann , Masami Hiramatsu , Linus Torvalds , , , , , , References: <20200521152301.2587579-1-hch@lst.de> <20200521152301.2587579-13-hch@lst.de> <20200527190432.e4af1fba00c13cb1421f5a37@linux-foundation.org> <2b64fae6-394c-c1e5-8963-c256f4284065@fb.com> <20200528043957.GA28494@lst.de> From: Yonghong Song Message-ID: Date: Thu, 28 May 2020 10:06:17 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.8.1 In-Reply-To: <20200528043957.GA28494@lst.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BY3PR04CA0020.namprd04.prod.outlook.com (2603:10b6:a03:217::25) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from MacBook-Pro-52.local (2620:10d:c090:400::5:454a) by BY3PR04CA0020.namprd04.prod.outlook.com (2603:10b6:a03:217::25) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3045.19 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 278fbe6b-98ee-444c-8673-08d80329716f X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 May 2020 17:06:20.7410 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: bXZ/iBHo8JZOLnK0G2nipYyS7Q8UyWtDTAA/ELwEGBVm+PqR0S3DrFNOzm9Tmka5 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2901 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.687 definitions=2020-05-28_03:2020-05-28,2020-05-28 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 lowpriorityscore=0 suspectscore=0 mlxlogscore=742 spamscore=0 mlxscore=0 malwarescore=0 bulkscore=0 adultscore=0 phishscore=0 clxscore=1015 priorityscore=1501 impostorscore=0 cotscore=-2147483648 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005280119 X-FB-Internal: deliver Sender: linux-parisc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-parisc@vger.kernel.org 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! From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-00082601.pphosted.com ([67.231.153.30]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jeM05-0001sK-IT for linux-um@lists.infradead.org; Thu, 28 May 2020 17:07:27 +0000 Subject: Re: [PATCH 12/23] bpf: handle the compat string in bpf_trace_copy_string better References: <20200521152301.2587579-1-hch@lst.de> <20200521152301.2587579-13-hch@lst.de> <20200527190432.e4af1fba00c13cb1421f5a37@linux-foundation.org> <2b64fae6-394c-c1e5-8963-c256f4284065@fb.com> <20200528043957.GA28494@lst.de> From: Yonghong Song Message-ID: Date: Thu, 28 May 2020 10:06:17 -0700 In-Reply-To: <20200528043957.GA28494@lst.de> Content-Language: en-US MIME-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-um" Errors-To: linux-um-bounces+geert=linux-m68k.org@lists.infradead.org To: Christoph Hellwig Cc: linux-parisc@vger.kernel.org, Daniel Borkmann , netdev@vger.kernel.org, x86@kernel.org, linux-um@lists.infradead.org, Alexei Starovoitov , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Masami Hiramatsu , Andrew Morton , Linus Torvalds , bpf@vger.kernel.org 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! _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um