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[178.24.249.8]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a83838cfac5sm629789466b.80.2024.08.19.06.22.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 19 Aug 2024 06:22:22 -0700 (PDT) Message-ID: <3995846d-39a1-41c9-9544-b74d9dd50a6c@redhat.com> Date: Mon, 19 Aug 2024 15:22:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 3/4] mm: BUG_ON to avoid NULL deference while __GFP_NOFAIL fails To: Barry Song <21cnbao@gmail.com> Cc: Christoph Hellwig , akpm@linux-foundation.org, linux-mm@kvack.org, 42.hyeyoo@gmail.com, cl@linux.com, hailong.liu@oppo.com, hch@infradead.org, iamjoonsoo.kim@lge.com, mhocko@suse.com, penberg@kernel.org, rientjes@google.com, roman.gushchin@linux.dev, torvalds@linux-foundation.org, urezki@gmail.com, v-songbaohua@oppo.com, vbabka@suse.cz, virtualization@lists.linux.dev, Lorenzo Stoakes , Kees Cook , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Jason Wang , Maxime Coquelin , "Michael S. Tsirkin" , Xuan Zhuo References: <20240817062449.21164-1-21cnbao@gmail.com> <20240817062449.21164-4-21cnbao@gmail.com> <5654b71c-1d9d-4c48-b28b-664662da8897@redhat.com> <416ac265-ced2-4f90-a347-0a256edf7fdf@redhat.com> <54a4619d-e826-465e-9a0f-0a8f37798e15@redhat.com> <20240819124924.GA7642@lst.de> <9f4fa8cf-df02-463d-9715-087a7cd6fc88@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 48FD5100007 X-Stat-Signature: g7sgw8pebrrubm8r93k1itxkk69s8rgi X-HE-Tag: 1724073746-632728 X-HE-Meta: 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 YQ8u3Ous 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 19.08.24 15:19, Barry Song wrote: > On Tue, Aug 20, 2024 at 1:10 AM David Hildenbrand wrote: >> >> On 19.08.24 15:05, Barry Song wrote: >>> On Tue, Aug 20, 2024 at 12:51 AM David Hildenbrand wrote: >>>> >>>> On 19.08.24 14:49, Christoph Hellwig wrote: >>>>> On Mon, Aug 19, 2024 at 02:33:06PM +0200, David Hildenbrand wrote: >>>>>> It should all be caught during testing either way. And if some OOT module >>>>>> does something nasty, that's not our responsibility. >>>>>> >>>>>> BUG_ON is not a way to write assertions into the code. >>>>> >>>>> So you'd rather create exploits than crashing on a fundamental API >>>>> violation? That's exactly what the series is trying to fix. >>>> >>>> I'd rather have a sane API that doesn't even allow this level of >>>> flexibility with NOFAIL. >>> >>> yes, i have already sent a RFC enforcing direct_reclamation: >>> https://www.spinics.net/lists/linux-mm/msg394659.html >>> >>> somehow, it is not ready yet. i think Christoph prefers scope >>> api rather than GFP_NOFAIL which definitely has >>> __GFP_DIRECT_RECLAIM set. I guess you know I have >>> at least 5 series running, so it will happen soon though. >> >> That really sounds like the right thing to do, at least with the "direct >> reclaim" problem ... >> >>> >>>> >>>> But probably I'm missing more details here why this all has to be so >>>> complicated ;) >>> >>> enforcing direct_reclamation is right and will work for a reasonable size. >>> but for this overflow size, even if we enforce direct_reclamation >>> in GFP_NOFAIL, we are still failing. >> >> Right, someone requested something completely impossible. It's harder to >> do something here that doesn't return NULL. Except WARN_ON_ONCE() and >> loop for all infinity. > > Returning NULL can introduce security vulnerabilities. While I’m not a hacker, > it’s hard to predict how they might exploit this. If we want to avoid using > BUG_ON, an alternative approach could be as follows: > > while(gfp & __GFP_NOFAIL) some_cpu_relaxed_job; ? At least for the "allocate something impossible in size", retrying forever makes *some* sense (with a warning, of course). We would retry until it works for sizes that are possible. For the other case, we should just make __GFP_NOFAIL imply whatever is currently a "must". Returning NULL here is indeed strange. -- Cheers, David / dhildenb