From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.240 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793421256; b=CXF+lGK4nnfKbNwXkqBMPbuFQ4nqp6QObiOQZOon04LIhDqNOl73m/lPsjF+EfgI9o+Y e15sNg57+pcYMczuM8pJWIp6aoMrz/qxpgSSgUZ1uNKfZF9kzvehgKLoXBXStOoFhtZNx cQBjkGpDpR1tkeTaYNxfGZN6NrdtQqtJ3gD8u8kMZhSx1F2qCIDSAJbyH332mewGZ5a1F UEVhWdpRLhywk80QwklRnH/kRmT7vy49EM0PSAtMVhYOGqmm+4Sf2wSFbqzYxgivNhdXs kWf4hLlYNpNJ9tZRS7L/ts0JUi8Wvx036mTn/xxzaS/QH2apW220DDoqqGoTArQ8tlQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793421256; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Date:From:To:Cc:Subject:Message-ID: X-B4-Tracking:X-Change-ID:X-Mailer:MIME-Version:Content-Type: Content-Disposition; bh=Flx6BFpBHU/1mQwNgXF0H0qYyTFKKY1odWtVjJY4UAU=; b=xQkQI5ihOsKRLPzSGC+n6b9wTDqeCQFytS/8dQ8TVpnXXwe3t0cvBWUMtnZ04ZJvQ6l4 347jO9lKtbJYPvomwhAXCjJW59zUWIc8tZwgJn7ztPC8tIT6heSFKD2PuC8EXqu4sYnVU 2Ld/WVTvK6jvG+XwaVHLV+YQQKA2U8GNbNfd7zr9Oz/WVRqnw4j1gGOMGL60/dRWsZAu6 6WiQ2VsQ2CzXtvwlJ46lH19fK/SuvJqogmyUi7cJ0G0NpraMgg9AZ35hOFg5OD7VjFhAT tZ06HwTEEnUaKb7qXYZFhPxMNER67W8iutJakMoNjVHo75s0Vs8MvAtSNycGYA6mdpg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=dfA3sF3O; arc=none smtp.remote-ip=95.215.58.240 Received: from mta1.migadu.com (out-240.mta1.migadu.com [95.215.58.240]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B901B606A31C for ; Sat, 31 Oct 2026 04:34:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org B901B606A31C Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=dfA3sF3O X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=sRRglwrZgXV0SrK/OtUomTWdFA+5PNai7nUeEM2ufrs=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793421253; v=1; x=1794026053; b=dfA3sF3OjfsnSyAXxygps3E5xBqKVi8PVPQwEBwBYiC8Ivlyw64CIRv2XWJn8WzS/lBrwj6P Y+WZcoRkzXd3JehipnlmIX1nYaDmvOIzsib7XKbkj/wYYfDyN4vAHYhH072gBgRruKBd4AuVu8r Edhk6d3kxe6eIoHy4p9AMoVQ= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 84ce8c3f7c47124b; Sat, 31 Oct 2026 04:34:08 +0000 X-Mizu-Trace-ID: 84ce8c3f7c47124b X-Migadu-Flow: FLOW_OUT Date: Sat, 31 Oct 2026 04:33:59 +0000 From: "Jose Fernandez (Anthropic)" To: "Matthew Wilcox (Oracle)" , Jan Kara , Andrew Morton , David Hildenbrand Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Krystian Kaniewski , stable@vger.kernel.org, "Jose Fernandez (Anthropic)" Subject: [PATCH v2] mm/filemap: stop fault-around when the walk steps back Message-ID: <20261031-jf-mm-filemap-map-pages-lower-bound-v2-1-21029744e589@linux.dev> X-B4-Tracking: v=1; b=H4sIACVu5WoC/yXNyw6CMBCF4Vchs3YSqAmpvopxMbRTHEIvaUVNC O9ugcVZfJv/rFA4Cxe4Nytk/kiRGCrUpQHzojAyiq0G1aq+a5XGyaH36GRmTwn3JRq54By/nHG IS7BIvbqy1aQ7c4NaSpmd/I6Xx/N0WYaJzXtPw7b9AbLiH4eHAAAA X-Change-ID: 20261028-jf-mm-filemap-map-pages-lower-bound-a623ed8a81c9 X-Mailer: b4 0.15.2 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-Disposition: inline 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. Link: https://lore.kernel.org/20260904121301.200049-1-krystianmkaniewski@gmail.com [1] Fixes: 6b24ca4a1a8d ("mm: Use multi-index entries in the page cache") Cc: stable@vger.kernel.org Signed-off-by: Jose Fernandez (Anthropic) --- Changes in v2: - Add Fixes: and Cc: stable tags, and say in the message that the loop can also write out of bounds (David Hildenbrand). https://patch.msgid.link/0a1ad7d2-ff0e-4248-8f03-2a64a9134aae@kernel.org - Link to v1: https://patch.msgid.link/20261028-jf-mm-filemap-map-pages-lower-bound-v1-1-0bf126e876d4@linux.dev --- mm/filemap.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/mm/filemap.c b/mm/filemap.c index b74bc1e5015c..1df776907140 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3968,6 +3968,13 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, unsigned long end; vm_fault_t map_ret; + /* A lower index could move vmf->pte out of its page table. */ + if (unlikely(xas.xa_index < last_pgoff)) { + folio_unlock(folio); + folio_put(folio); + break; + } + addr += (xas.xa_index - last_pgoff) << PAGE_SHIFT; vmf->pte += xas.xa_index - last_pgoff; last_pgoff = xas.xa_index; --- base-commit: 65ba8f34ec886ec72b2c07ddc8cf3d815c32869d change-id: 20261028-jf-mm-filemap-map-pages-lower-bound-a623ed8a81c9 Best regards, -- Jose Fernandez (Anthropic)