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(p200300d82f1ded001769dd7c7208eb33.dip0.t-ipconnect.de. [2003:d8:2f1d:ed00:1769:dd7c:7208:eb33]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4562e819e04sm24699575e9.18.2025.07.16.08.31.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Jul 2025 08:31:50 -0700 (PDT) Message-ID: Date: Wed, 16 Jul 2025 17:31:49 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] mm/huge_memory: prevent potential NULL pointer dereference To: Zi Yan Cc: Antonio Quartulli , linux-mm@kvack.org, Andrew Morton , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Dan Carpenter References: <20250716145804.4836-1-antonio@mandelbit.com> <955c523e-9eea-48fb-a604-9ec445e563f4@redhat.com> <120D580D-43F0-4B71-BD03-A74CEB65889B@nvidia.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/g1oFAmgsLPQFCRvGjuMACgkQTd4Q 9wD/g1o0bxAAqYC7gTyGj5rZwvy1VesF6YoQncH0yI79lvXUYOX+Nngko4v4dTlOQvrd/vhb 02e9FtpA1CxgwdgIPFKIuXvdSyXAp0xXuIuRPQYbgNriQFkaBlHe9mSf8O09J3SCVa/5ezKM OLW/OONSV/Fr2VI1wxAYj3/Rb+U6rpzqIQ3Uh/5Rjmla6pTl7Z9/o1zKlVOX1SxVGSrlXhqt kwdbjdj/csSzoAbUF/duDuhyEl11/xStm/lBMzVuf3ZhV5SSgLAflLBo4l6mR5RolpPv5wad GpYS/hm7HsmEA0PBAPNb5DvZQ7vNaX23FlgylSXyv72UVsObHsu6pT4sfoxvJ5nJxvzGi69U s1uryvlAfS6E+D5ULrV35taTwSpcBAh0/RqRbV0mTc57vvAoXofBDcs3Z30IReFS34QSpjvl Hxbe7itHGuuhEVM1qmq2U72ezOQ7MzADbwCtn+yGeISQqeFn9QMAZVAkXsc9Wp0SW/WQKb76 FkSRalBZcc2vXM0VqhFVzTb6iNqYXqVKyuPKwhBunhTt6XnIfhpRgqveCPNIasSX05VQR6/a OBHZX3seTikp7A1z9iZIsdtJxB88dGkpeMj6qJ5RLzUsPUVPodEcz1B5aTEbYK6428H8MeLq NFPwmknOlDzQNC6RND8Ez7YEhzqvw7263MojcmmPcLelYbfOwU0EVcufkQEQAOfX3n0g0fZz 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+DWgUCaCwtJQUJG8aPFAAKCRBN3hD3AP+DWlDnD/4k2TW+HyOOOePVm23F5HOhNNd7nNv3 Vq2cLcW1DteHUdxMO0X+zqrKDHI5hgnE/E2QH9jyV8mB8l/ndElobciaJcbl1cM43vVzPIWn 01vW62oxUNtEvzLLxGLPTrnMxWdZgxr7ACCWKUnMGE2E8eca0cT2pnIJoQRz242xqe/nYxBB /BAK+dsxHIfcQzl88G83oaO7vb7s/cWMYRKOg+WIgp0MJ8DO2IU5JmUtyJB+V3YzzM4cMic3 bNn8nHjTWw/9+QQ5vg3TXHZ5XMu9mtfw2La3bHJ6AybL0DvEkdGxk6YHqJVEukciLMWDWqQQ RtbBhqcprgUxipNvdn9KwNpGciM+hNtM9kf9gt0fjv79l/FiSw6KbCPX9b636GzgNy0Ev2UV m00EtcpRXXMlEpbP4V947ufWVK2Mz7RFUfU4+ETDd1scMQDHzrXItryHLZWhopPI4Z+ps0rB CQHfSpl+wG4XbJJu1D8/Ww3FsO42TMFrNr2/cmqwuUZ0a0uxrpkNYrsGjkEu7a+9MheyTzcm vyU2knz5/stkTN2LKz5REqOe24oRnypjpAfaoxRYXs+F8wml519InWlwCra49IUSxD1hXPxO WBe5lqcozu9LpNDH/brVSzHCSb7vjNGvvSVESDuoiHK8gNlf0v+epy5WYd7CGAgODPvDShGN g3eXuA== Organization: Red Hat In-Reply-To: <120D580D-43F0-4B71-BD03-A74CEB65889B@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: RVSg_iUWeBAkVJMZoXvhvOZyD33yRra0acRMO1B-2eQ_1752679913 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: dyeemopz8own7353in1b13mqhuth8spe X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: C543DC0016 X-Rspam-User: X-HE-Tag: 1752679916-29202 X-HE-Meta: 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 ABj07Td2 BxypbeHo0PDvKSwYmqBfkBKX1rk+pdkWmB78AKiUBRBEwCSi4OEPhdN+2tIfy5CA85IUweWrgPw0G25T7VI4/DeO0ew== 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 16.07.25 17:24, Zi Yan wrote: > On 16 Jul 2025, at 11:18, David Hildenbrand wrote: > >> On 16.07.25 17:10, Zi Yan wrote: >>> On 16 Jul 2025, at 10:58, Antonio Quartulli wrote: >>> >>>> I just found this issue in the last linux-next Coverity report and it >>>> caught my attention. >>>> I am not familiar with this code, therefore I am sending this patch >>>> as RFC because I am not 100% sure whether this is a false positive or >>>> not. >>>> However, it seems potentially legit to me: >>>> >>>> In __folio_split(), when looping over folios we dereference >>>> `mapping` before ensuring it is non-NULL. >>>> >>>> Following code in the loop body performs such check, thus >>>> suggesting that `mapping` may be NULL and accessing it >>>> without any check may be dangerous. >>>> >>>> Add NULL check before passing it to shmem_mapping(). >>>> >>>> Cc: Zi Yan >>>> Fixes: 00527733d0dc ("mm/huge_memory: add two new (not yet used) functions for folio_split()") >>>> Addresses-Coverity-ID: 1647614 ("FORWARD_NULL") >>>> Signed-off-by: Antonio Quartulli >>>> --- >>>> mm/huge_memory.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>>> index 389620c65a5f..d649026db95a 100644 >>>> --- a/mm/huge_memory.c >>>> +++ b/mm/huge_memory.c >>>> @@ -3802,7 +3802,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order, >>>> >>>> /* Some pages can be beyond EOF: drop them from cache */ >>>> if (new_folio->index >= end) { >>>> - if (shmem_mapping(mapping)) >>>> + if (mapping && shmem_mapping(mapping)) >>>> nr_shmem_dropped += folio_nr_pages(new_folio); >>>> else if (folio_test_clear_dirty(new_folio)) >>>> folio_account_cleaned( >>> Hi Antonio, >>> >>> Is there a way of preventing Coverity/sparse from checking certain code? >>> This non-NULL mapping issue pops up every time I touch the code. >> >> Probably we could make that code more readable and achieve it: >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 24aff14d22a1e..acf56aae1a2ef 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -3775,6 +3775,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order, >> */ >> for (new_folio = folio_next(folio); new_folio != next_folio; >> new_folio = next) { >> + unsigned long nr_pages = folio_nr_pages(new_folio); >> next = folio_next(new_folio); >> expected_refs = folio_expected_ref_count(new_folio) + 1; >> @@ -3782,20 +3783,20 @@ static int __folio_split(struct folio *folio, unsigned int new_order, >> lru_add_split_folio(folio, new_folio, lruvec, list); >> - /* Some pages can be beyond EOF: drop them from cache */ >> - if (new_folio->index >= end) { >> - if (shmem_mapping(mapping)) >> - nr_shmem_dropped += folio_nr_pages(new_folio); >> - else if (folio_test_clear_dirty(new_folio)) >> - folio_account_cleaned( >> - new_folio, >> - inode_to_wb(mapping->host)); >> - __filemap_remove_folio(new_folio, NULL); >> - folio_put_refs(new_folio, >> - folio_nr_pages(new_folio)); >> - } else if (mapping) { >> - __xa_store(&mapping->i_pages, new_folio->index, >> - new_folio, 0); >> + /* Add the new folio to the page cache ... */ >> + if (mapping) { >> + /* ... however, drop folios beyond EOF. */ >> + if (new_folio->index >= end) { >> + if (shmem_mapping(mapping)) >> + nr_shmem_dropped += nr_pages; >> + else if (folio_test_clear_dirty(new_folio)) >> + folio_account_cleaned(new_folio, inode_to_wb(mapping->host)); >> + __filemap_remove_folio(new_folio, NULL); >> + folio_put_refs(new_folio, nr_pages); >> + } else { >> + __xa_store(&mapping->i_pages, >> + new_folio->index, new_folio, 0); >> + } >> } else if (swap_cache) { >> __xa_store(&swap_cache->i_pages, >> swap_cache_index(new_folio->swap), >> >> >> Having that logic in a helper would be cleaner, but not straight-forward due >> to things like nr_shmem_dropped. > > Looks good to me. Do you want to send a patch? Otherwise, I can send one. Please send on (you'll manage to clean this up further). Thanks! -- Cheers, David / dhildenb