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[2003:d8:2f31:700:3851:c66a:b6b9:3490]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4532de8c2d2sm173294185e9.1.2025.06.17.01.28.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Jun 2025 01:28:59 -0700 (PDT) Message-ID: Date: Tue, 17 Jun 2025 10:28:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/madvise: initialize prev pointer in madvise_walk_vmas To: Lorenzo Stoakes Cc: Lance Yang , akpm@linux-foundation.org, 21cnbao@gmail.com, Liam.Howlett@oracle.com, vbabka@suse.cz, jannh@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Lance Yang References: <20250617020544.57305-1-lance.yang@linux.dev> 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-MFC-PROC-ID: W-N5ZGTZxbOeN0fiioVJx1-0Zkn_HtYASP_g937IFjI_1750148940 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 84DFC180002 X-Stat-Signature: bmisikby9uibhde5xd33ftftcss44wcm X-Rspam-User: X-HE-Tag: 1750148943-701020 X-HE-Meta: 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 cqh+nij8 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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 17.06.25 10:21, Lorenzo Stoakes wrote: > On Tue, Jun 17, 2025 at 09:54:29AM +0200, David Hildenbrand wrote: >> On 17.06.25 04:05, Lance Yang wrote: >>> From: Lance Yang >>> >>> The prev pointer was uninitialized, which could lead to undefined behavior >>> where its address is taken and passed to the visit() callback without being >>> assigned a value. >> >> So, we are passing the pointer value to visit(), which is not undefined >> behavior. >> >> The issue would be if anybody takes a look at the value stored at that >> pointer. Because, already passing an uninitialized value to a (non-inlined) >> function is undefined behavior according to C. >> >> In madvise_update_vma()->vma_modify_flags_name() we do exactly that, >> correct? > > Err the parameter there is struct vm_area_struct **prev... > > We deref to the prev ptr which is unassigned yes but the pointer to the pointer isn't... > struct vm_area_struct *prev; is uninitialized. We pass &prev -> prevp, which now points at something uninitialized. Doing "*prevp =" is fine, because we will initialize. Doing "= *prep" is not fine, because the value was not initialized. >> >> vma = vma_modify_flags_name(&vmi, *prev, ... >> >> We should use Fixes: then. > > So no we shouldn't... > >> >> >> Acked-by: David Hildenbrand > > Sure? :) Unless I am missing something important, yes :) -- Cheers, David / dhildenb