From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.187 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793289047; b=SM61WNXBIMQ2jzxeayWZlk2L5+IL9sN+zcfu9ZiE35Ejf5d8AK+PLCPewDemG4376ffP H2SUlGsBqYB5Chd1wW6BZR5e6nc6/Glu0bZrZTGHNosZ8THTC/K2yoJy6cxXGi9oe8T+s lwDxTW91fp589EL2+/1ncPwJ5VWFSVCF19Ebi6tod0WxcofPrapyvvQsnmtUSy6RBU3PS 8QLzIWbw5jfxtOEV8G7ytKeeVm7N9LNNSz6Xb5NqGAO+OR+5+OOKHjBSuZuOWgi8VPM1o gT3andOfWgSUN8BXI4qa+lqU22TBom7Byo5cyb0xymLXcXLvvdqVesjjdlRyY8mvcGg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793289047; 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=yaAYz8Hc0E1J++0lVxAIJTRPnroDQ9MIhn/HfIw3mGs=; b=rM3Hwx647jkeOFSwlNlsf5uv8PAtxCqzlZJ60+17LMu6a2QtFEGY+qQDkiXUKcu3ywdb XYhDbG8Wm3U4nKYrGbzvVMKMNHiu8CiBzFshrWSDv+2ynbWCVVosH0uIWs908yd4X2lPc HdACK48hFQpFRdo9umvQcuL0mB+rE6mjUc7usl7FPnCybrvdKYeuHeb4AVhzmq3FkVhig a9+9eHSVAvwSph4JxTrJPvi+lux0aKu7Qw8Qv6SpqKzfN9niFf8b0OJne/KheGVGclFre YaQo3ZKPDYYFHzcL0TgYGZomAiabqdZm6vSaYM92UHzQNz83sHaQxhtGCCXvUmkz8zA== 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=jp2EfrI4; arc=none smtp.remote-ip=95.215.58.187 Received: from mta1.migadu.com (out-187.mta1.migadu.com [95.215.58.187]) (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 6381C606A332 for ; Thu, 29 Oct 2026 15:50:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 6381C606A332 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=jp2EfrI4 X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=n9CMCDalShVTKhOhD+z5DJppXsi7YqvLnst8+Zhlhxk=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793289044; v=1; x=1793893844; b=jp2EfrI4BVBGN2zknGopZvCy+T/xY7ruX+Rl8f78cl08kZqIUKG058Yr5eU5pnNopGhE5qsE T0/y0iooL1vrTn9B54OCE8Z6i9vf6+egbewXom685DJu3Qz9gsLTifwpI7jznX/fG1UBE/D4GTm 6lSJlF2DfLbRrRt8aW3b0P9o= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 43b22051bb286e53; Thu, 29 Oct 2026 15:50:44 +0000 X-Mizu-Trace-ID: 43b22051bb286e53 X-Migadu-Flow: FLOW_OUT Date: Thu, 29 Oct 2026 15:50:40 +0000 From: "Jose Fernandez (Anthropic)" To: "Matthew Wilcox (Oracle)" , Jan Kara , Andrew Morton Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand , Krystian Kaniewski , "Jose Fernandez (Anthropic)" Subject: [PATCH] mm/filemap: stop fault-around when the walk steps back Message-ID: <20261028-jf-mm-filemap-map-pages-lower-bound-v1-1-0bf126e876d4@linux.dev> X-B4-Tracking: v=1; b=H4sIAHuF4moC/yXNywrCMBCF4Vcps3agiVCiryIupsmkTmkuJFaF0 nc31cVZfJv/bFC5CFe4dhsUfkmVFBvUqQP7oDgximsG3etB9drg7DEE9LJwoIzHMk1ccUlvLji mNTqkQZ/ZGTLKXqCVcmEvn9/L7f53XceZ7fNIw75/AQGVreeHAAAA 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]. 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] Signed-off-by: Jose Fernandez (Anthropic) --- 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)