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=1793640472; b=DW/qnikbEaZpsFDPE/3rgTMtzxWo/NBeO0m12b71tcjRKek2BacxiTBqHduNpRWZ8Ts9 8ahKab2s05mwwmxTz+pp7iytgxpdzs5fCnqj/X8NA34mVdbVph63TDRYAZDtRZVylRAlL XgGIal+XQMGpd05OcUncIwjNXuG4ZDXhIt5FlJQ0Zsb2FRFsdYt1xRif8v8AhUEOPDrhs Ed8IlzrNjyclhjeFet10sMrkx8ekk1xpLkSciy3Z0aj9Prx3HvmOmWxdOdg5atDcVbizG ru8IDkDIMSYShYipvUTqQWSS18GIWIxK22e+fq9BoMMXInjcSrEYmx/5R/yG+X4POpg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793640472; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-Id: In-Reply-To:References:X-Mailer:Mime-Version:Content-Type: Content-Transfer-Encoding; bh=leKsCN/AW0CIMV0Z58FExykl0a+UkP/KW/e3nsnHLQM=; b=rdwiLKn12cNY+JrxpyLDoD97vnpWGpmcwny4KVSTLNvhnhXBKnYEg0yXsQfOqAud+Dcf deWgoVaOKKFvFFGACy3e7DllXLYGR0MWomSBDHGwxFphlighiFgnsU1so4iSxpTKnwqb5 GihGHMAIkpmFKLVwSX9LTl9+x/bsu0EgoUkw9kGHGHRFyLKyH2U/6U6/R3hOpk7TJNJDl qERgkcmHI6JJ+wUlb1MvODr0pswX5Uk8HoIriYTHCS1ZRBebUe+H8iysCLgGhv/JySVGp hkV8gdNfK50IK3/gd4eAhY39d5EJOJrLPnWV4kNLG8dEcaVlwwJm1v9VKxk8PVHCljw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=hCGUwl5E; 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 7F063606D82E; Mon, 2 Nov 2026 17:27:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=hCGUwl5E Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8D29A1F00A17; Mon, 2 Nov 2026 17:27:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1793640471; bh=leKsCN/AW0CIMV0Z58FExykl0a+UkP/KW/e3nsnHLQM=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=hCGUwl5E2q8xC3fuwYjC4VbJ0KmGUnWBIucbBnmAQ1vd3ngEy7yXbM4BCpaxwfXNj IhAZLA/WXHfX9ARMw69lYseQ7Vc5+vSFUh7v+FhlXPadvqEAr2T9l+RQI1sK8KSBM6 PseChT1NMSI3bz7QCXmm5cSTyDOiG6BIlu/XVPuQ= Date: Mon, 2 Nov 2026 09:27:50 -0800 From: Andrew Morton To: "Jose Fernandez (Anthropic)" Cc: "Matthew Wilcox (Oracle)" , Jan Kara , David Hildenbrand , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Krystian Kaniewski , stable@vger.kernel.org Subject: Re: [PATCH v2] mm/filemap: stop fault-around when the walk steps back Message-Id: <20261102092750.e53073b2c7b872f9d70c0711@linux-foundation.org> In-Reply-To: <20261031-jf-mm-filemap-map-pages-lower-bound-v2-1-21029744e589@linux.dev> References: <20261031-jf-mm-filemap-map-pages-lower-bound-v2-1-21029744e589@linux.dev> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sat, 31 Oct 2026 04:33:59 +0000 "Jose Fernandez (Anthropic)" wrote: > filemap_map_pages() can dereference a PTE pointer outside the page table > it locked. KASAN has reported this as a use-after-free read [1]. The > same path can also write out of bounds. When the stray entry reads as > none, the fault-around loop maps a page there with set_pte_range(). > > Its fault-around loop walks the page cache and moves vmf->pte by the > change in index. A lower index moves it back. xas_find() can step back > to a lower index when a multi-index entry is split during the walk. > > [1] fixes xas_find(), but the loop still relies on the walk never > stepping back. Stop the fault-around when the walk steps back. ->fault() > maps the faulting page if the loop did not. Thanks. Can I add your tested-by to [1]? > Link: https://lore.kernel.org/20260904121301.200049-1-krystianmkaniewski@gmail.com [1] "xarray: fix index jumping backwards in xas_find()".