From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6003E3D3D07 for ; Wed, 25 Mar 2026 15:24:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774452276; cv=none; b=P+z55U8VF6gyWFYxUDCAyy2ICv1LgWTCx03u56sXLSayw17teg377Ad+L2AldMqAFEc/Tfpvu8rD9vSoO8WEzidYtDRuwIpx1NZzVniA6Z2FEEIpfT7dhoMByW2iiJeOInXOOL86zbHIN0EwWytNS7AqlYmqRIe6fQoQw7+yUmQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774452276; c=relaxed/simple; bh=CvCkYeIxBeSF+4kW5iTX2aH4Uo4OeNuvaWXY2mOVVBU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=u/ECw+KTwDAmAWccC0wUQXStur/iZgTmZFiw/T6fXQAG0mDpeg6X/w+1MkZbQiMwNZRjYFt+FqcsTRD6Qbcd5chFv2ngKj/j5rzpntLEEhXYP+lvGeDgOubz01A2TBKvkEXcDXVKQgX5S3Ls6HgIJCchrhIjUsW2biJr/AXVGak= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GTjsV3ov; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GTjsV3ov" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E0577C4CEF7; Wed, 25 Mar 2026 15:24:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774452276; bh=CvCkYeIxBeSF+4kW5iTX2aH4Uo4OeNuvaWXY2mOVVBU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=GTjsV3ovCtsUP2jZmJD6YZaU0o0OAnZ6CziIpQB1w4USl4W7v34PUQ1DT38XlTfXo OR+gmanvcUo2BbtCZuAthZug4MsT8QcoMwLM645HBJEqQea2MJrcqBjRUT6mJfGPnh 7aKjQHBohQ3mo0VLR2B7iSnn/tsl13efatj/F6v1keotNVjp5gx6f9sDeeXFVCNQDB ZQEcG40hyaLOSFoUxu+kK7HjRWQUrH+JS2oErULOLhXDrYwk2A0Nv3ZRkGUdU0UIw4 I1EOtRgzBRdE3aDKKlBBepStxOMLbRYb9fz1SrJ7BZeVbzpfPqTbWgdkDxAoddGEr7 aKD86SauNu9ZA== Message-ID: <90361397-395d-446b-b1a5-580efe23bb70@kernel.org> Date: Wed, 25 Mar 2026 16:24:29 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] futex: Use-after-free between futex_key_to_node_opt and vma_replace_policy To: Peter Zijlstra , Eric Dumazet Cc: Thomas Gleixner , Hao-Yu Yang , mingo@redhat.com, linux-kernel@vger.kernel.org, Andrew Morton , linux-mm@kvack.org, Lorenzo Stoakes , "Liam R. Howlett" References: <20260313124756.52461-1-naup96721@gmail.com> <87a4vyihlx.ffs@tglx> <20260324140019.GE3738010@noisy.programming.kicks-ass.net> <87fr5pgp5x.ffs@tglx> <20260324174418.GB1850007@noisy.programming.kicks-ass.net> <20260325151445.GH3738010@noisy.programming.kicks-ass.net> <20260325152206.GH3738786@noisy.programming.kicks-ass.net> 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: <20260325152206.GH3738786@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 3/25/26 16:22, Peter Zijlstra wrote: > On Wed, Mar 25, 2026 at 08:19:24AM -0700, Eric Dumazet wrote: >> On Wed, Mar 25, 2026 at 8:14 AM Peter Zijlstra wrote: >>> >>> >>> Bah, at that point we might as well RCU the thing like so, I suppose. >>> >>> --- a/mm/mempolicy.c >>> +++ b/mm/mempolicy.c >>> @@ -1026,7 +1026,7 @@ static int vma_replace_policy(struct vm_ >>> } >>> >>> old = vma->vm_policy; >>> - vma->vm_policy = new; /* protected by mmap_lock */ >>> + rcu_assign_pointer(vma->vm_policy, new); /* protected by mmap_lock */ >>> mpol_put(old); >>> >>> return 0; >>> diff --git a/kernel/futex/core.c b/kernel/futex/core.c >>> index 4bacf5565368..6336a80e3dca 100644 >>> --- a/kernel/futex/core.c >>> +++ b/kernel/futex/core.c >>> @@ -342,7 +342,7 @@ static int __futex_key_to_node(struct mm_struct *mm, unsigned long addr) >>> if (!vma) >>> return FUTEX_NO_NODE; >>> >>> - mpol = vma_policy(vma); >>> + mpol = rcu_dereference_raw(vma->vm_policy); >>> if (!mpol) >>> return FUTEX_NO_NODE; >> >> Yes, but sparse will bite :) > > Oh gawd, yes, and then people will go 'fix' it and it'll turn into an > unholy mess. > >> READ_ONCE()/WRITE_ONCE() on these two locations seems acceptable. > > Fair enough. Like so then.. > > --- a/kernel/futex/core.c > +++ b/kernel/futex/core.c > @@ -342,7 +342,7 @@ static int __futex_key_to_node(struct mm > if (!vma) > return FUTEX_NO_NODE; > > - mpol = vma_policy(vma); > + mpol = READ_ONCE(vma->vm_policy); > if (!mpol) > return FUTEX_NO_NODE; > > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -1026,7 +1026,7 @@ static int vma_replace_policy(struct vm_ > } > > old = vma->vm_policy; > - vma->vm_policy = new; /* protected by mmap_lock */ > + WRITE_ONCE(vma->vm_policy, new); /* protected by mmap_lock */ > mpol_put(old); > > return 0; LGTM, feel free to add my Acked-by: David Hildenbrand (Arm) -- Cheers, David