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b=blPOGtHHu1tq3dB00Ujh+vtvVYU+cG9XGGANoibb6V930ieUlGbThJR+UuVR5cEbd VDxHHioU5Hje8/Bmd1zSATXRtXaqJ9kl4uv8M/A2r1CF7seZT7bVSEoy53/lqc5FJU hjOb1vaWSnLDDFQP7W6iS9d+m9w9BjQqTReqGEnGK0c++AFP05BLJJZ6qpqfHYt0we tDS/J1Oom1CD5WxjzTCiI+tVn5uu8mJ6/9kWgudDMDN9VJvTniA8vjcs5F0p2RdjqQ VnkTzliosOQ4wMTZFG7/8Lwjt8/PHd78lWpeF3K2r+jObJgsTzLeBkEVrVTjApt3vN QRD3NcP3ba2ZA== Message-ID: Date: Sun, 25 Oct 2026 11:56:16 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fs/proc/task_mmu: pin mm_users in do_pagemap_scan() To: Ngoc Quy , akpm@linux-foundation.org, liam@infradead.org, ljs@kernel.org Cc: Vlastimil Babka , Jann Horn , Pedro Falcato , Muhammad Usama Anjum , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, stable@vger.kernel.org References: <20261014095540.3261469-1-ngocquy0700@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20261014095540.3261469-1-ngocquy0700@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 059BD1C0003 X-Spam-Status: No, score=-17.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: zbjoi56q8dtue4azxk5iep5hq93f3xj5 X-HE-Tag: 1792925824-709527 X-HE-Meta: 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 Yootk7Q9 jlI78FaUd5pICFQWCrDjFNDrbI2z0vitQxug5eWlQayD/o7GKhBri60Lnt2cwCLrFtTM2+idPE0Jh39hHO8NLXblkt0Kw7mcLMExfCoBddofgoo+d7vhGgM82wSyWGzbtc00xToY1zaxRh1Xvuv8hQspwLfXgkMJ4HJ5Lg2JChYqrm5++eW5y8FcxZy+kjb5tbvyvoPR6CdeTMx2NTKihMz8RpEmneqwk3q5ug4nmt8YFybnzkkx8RXan4eHpwWWe+TfVH9c8EfdK3a5J6kji+kpKEXTGkYBrRr4SIICtgr9b83bhWzfwy+sQcXd1RHAQPCQZ7+aruwmFpEv3qsslKHvh1iKubPrEHcjm Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/14/26 11:55, Ngoc Quy wrote: > The PAGEMAP_SCAN ioctl takes mmap_read_lock() on an mm obtained from > /proc//pagemap without holding a reference to mm_users. > > proc_mem_open() deliberately grabs only mm_count, so a consumer that > touches the address space has to call mmget_not_zero() first. Every > other consumer in this file does -- m_start(), do_procmap_query(), > show_smaps_rollup() and pagemap_read() -- but do_pagemap_scan() does > not. > > Without that reference the target can reach exit_mmap() concurrently, > and exit_mmap() calls unmap_vmas() while holding mmap_lock only for > reading, which does not exclude the scanner. For ordinary VMAs this is > harmless, as free_pgtables() and remove_vma() run afterwards under > mmap_write_lock. A shared hugetlb VMA is different: __hugetlb_zap_end() > frees the VMA's hugetlb_vma_lock inside the read-locked phase. > > walk_hugetlb_range() can therefore load vma->vm_private_data, have the > lock freed underneath it, and then down_read() a freed rw_semaphore. > The load happens before the freeing side clears the pointer, so this is > a use-after-free and not a NULL dereference. Any unprivileged user can > reach it with no huge pages configured, as hugetlb_reserve_pages() > allocates the lock before the VM_NORESERVE early return. > > Pin mm_users across the scan, the way the other consumers do. mmput() > from the exiting task can then no longer reach exit_mmap() while a walk > is in progress. > > Fixes: 52526ca7fdb9 ("fs/proc/task_mmu: implement IOCTL to get and optionally clear info about PTEs") > Cc: stable@vger.kernel.org > Assisted-by: Claude:claude-opus-5 > Signed-off-by: Ngoc Quy > --- > fs/proc/task_mmu.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 5c54aebe2118..8825b01f5e38 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -3231,15 +3231,18 @@ static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg) > size_t n_ranges_out = 0; > int ret; > > + if (!mm || !mmget_not_zero(mm)) > + return -ESRCH; > + > ret = pagemap_scan_get_args(&p.arg, uarg); > if (ret) > - return ret; > + goto out_mmput; > > p.masks_of_interest = p.arg.category_mask | p.arg.category_anyof_mask | > p.arg.return_mask; > ret = pagemap_scan_init_bounce_buffer(&p); > if (ret) > - return ret; > + goto out_mmput; > > for (walk_start = p.arg.start; walk_start < p.arg.end; > walk_start = p.arg.walk_end) { > @@ -3294,6 +3297,8 @@ static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg) > ret = -EFAULT; > > kfree(p.vec_buf); > +out_mmput: > + mmput(mm); > return ret; > } Acked-by: David Hildenbrand (Arm) -- Cheers, David