From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793109816; b=zOmvQyIT4adBHDGZcQuoTwHE8nkKceEaWN4gY2VKeNh+yxs7grIRDuIocLOy7r5+D4kq OiSovS3OKx9TPUpOZx3mMBtDrDZ3+ZI3z5wHqWcuha56qsYiAPzsum17VkQsHJvcDUHI5 ejJw1gFpeZzvD1IaedLkNhW4gb/EQteNTE4MbvZzqQ4PDyLeZDhv3uC79PkslYaJo9NMI 6Rw3xS+JX4TKBJe54tOuAN9o0tHzYs0K8lqsWVPoPnsumIIOIGBJUVBzuBhNwgiSGIi1k qME7lXlj1pAkDVeu2cMKy2T8GTY6mjbfK9crxP30mgrFW3O2kqyPPt08JAHGgIyL9EA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793109816; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=H7+62nSvr3logypM0kC8CKxhrNR+3HtbHXcVAr7jUl8=; b=rc3rxC3dS+nQ/z9m8Z5O8SQZr+3lc4of62A3yJ6pukpLSJCjR/nc2e8DyB1UnzVl5W9d USQYd+9gG3tQjLTzHerwRMBQ+vjSKblJSr7Y0JqfoXrkpWZJmC0w620D/ZD1CMAHMNDoP dGBM1h/DwBA0GkIpJqK5qu8fNNENLaupEAnxNyobYtI1wt1zKCKQ+IyMygwgqOIsMn+6g MLw+4XXLCrdebAPv2lqgI9i46tlIx6a8X6tKKDB5H91p0bQV7k3za7+q28OQ7l9FMyWko NKvde1o1bOBSh6gVBaBxN3gVKwobfxHaeN6qnoeiLYYOT4F3pMoA52pdoLkodxj91LA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=o3eDX4T0; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 11829606A329 for ; Tue, 27 Oct 2026 14:03:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=o3eDX4T0 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 778201F01825; Tue, 27 Oct 2026 14:03:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793109815; bh=H7+62nSvr3logypM0kC8CKxhrNR+3HtbHXcVAr7jUl8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=o3eDX4T0rpxCCMFsMX5Uwkd50yBNb9chbe0AZx1MED/SRMSafPsJIkc8Zm8hPSFnn OcVKFE0h/qu7zcraWe2Fc2dBEWYSGeL9fH1q0VpuW7MEWuu9qzkqOin0xdLQv0yO66 j9gOtm5KoTZuNqOorCM1af4Bc8bIXRviypIpGKZKgzQcdcnVvG6lFksAYi1TAJZcr5 4T+rrW7kaMs+gPGXWVetjVPmrcXdDiuPdtyZdB+ShAy5Ng5dQqpuwBFTVRcOFwX8H9 MwP/Tp0iarGtbGhGBZCDFOlN7fIo5a8iQDnSW9lWitM4M4CrEHoezzZ54YSbpUTyhk TXGGHrXO6DGDQ== Message-ID: <752bd947-78ae-463f-8d3a-ec4ed35cd9e8@kernel.org> Date: Tue, 27 Oct 2026 15:03:30 +0100 X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fs/proc/task_mmu: pin the mm during PAGEMAP_SCAN To: Kyle Zeng , linux-mm@kvack.org Cc: Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pedro Falcato , stable@vger.kernel.org References: <20261024035646.68348-1-kylebot@openai.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: <20261024035646.68348-1-kylebot@openai.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/24/26 05:56, Kyle Zeng wrote: > A pagemap file holds an mm_count reference, not an mm_users reference. > Unlike pagemap_read(), do_pagemap_scan() does not acquire a live-MM > reference before walking the page tables. Its mmap read lock does not > exclude the first phase of exit_mmap(), which also unmaps VMAs under the > read lock. > > A process retaining a pagemap descriptor can therefore race the final > mmput() and access resources that have already been released. In > particular, a concurrent last userfaultfd close can free a context still > reachable through a dying MM's VMAs, and unmap_vmas() can free a shared > HugeTLB VMA's lock while the page walker is entering down_read(). KASAN > reports both a userfaultfd context read-after-free and a HugeTLB rwsem > write-after-free with unprivileged, read-only PAGEMAP_SCAN requests. > > Acquire mmget_not_zero() after validating the ioctl arguments and keep > the reference for the entire scan, including across mmap lock drops and > MMU-notifier operations. Return -ESRCH if the MM is already dead, as > PROCMAP_QUERY does. Balance the reference on the bounce-buffer allocation > failure path and at the common exit. The pagemap file continues to hold > only its existing mm_count reference between operations. > > Fixes: 52526ca7fdb9 ("fs/proc/task_mmu: implement IOCTL to get and optionally clear info about PTEs") > Cc: > Signed-off-by: Kyle Zeng > --- > I have a reproducer for this issue. > > fs/proc/task_mmu.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 5c54aebe2118..d2cee8dcba58 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -3235,11 +3235,14 @@ static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg) > if (ret) > return ret; > > + if (!mmget_not_zero(mm)) > + return -ESRCH; > + > 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_mm; > > 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_mm: > + mmput(mm); > return ret; > } > > Please take a look at the list before posting. https://lore.kernel.org/r/20261014095540.3261469-1-ngocquy0700@gmail.com -- Cheers, David