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=1794630761; b=Sh3cKP2XNe/m3AhTX7tSfyWwX5BMOEMkURM5YcnwVXHMW8ipT9isIGRkFLq8Sc0G8mdS iMEqTVuQQ17NJMzmO3lWM9R6lUojYOsykRckpRhXhc0V0pIB6rxo4kM3vKo7V7l8MdQUW Ni6jfYwoump4/8k6VjSPevw2/J2j8Zpkx6CPtJFYPmszXB27OP+PqJDLEwn1lG/HsKHhb 6WndBz2opoC966QvcvTTuCAfcptrNbRZeP3AL8u+KBo/5dYwIh6vY+0rNNqVZWqCxNs/9 PTCWuN3Kb/kjPVzMC/rks4hhPxmY+4dNW+sEDA8Kx59DJD17QY/+jCTofGkpkwyH6Uw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794630761; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=rUDtpGvWiJFYHdFOYuGZNchwlTnQhy0ujviPe6R/iX8=; b=iiNuhoG4flr9uMjgbeBY8NA+w3NelZTODNSpbAzXHqTylufGAUNIkB+ntQ0GIIqfTDrr ZE22vdCw/UCBUXTfNOJnhToDvEsgWEmRjSfyCGnvXKpRZIick1taW5t+zzO0WxxQLbS0G aUxXciotWuTVMHdfH/oEV3nTCG16SElwA7ipmXG6PGWGHP8o8rXVq9Tcd5/0MTqe2zIvq ur0v3WsUDPGku1NpyG8emdcjjT1gesymuTSJWEYOF8voHZ1TYYfinPW2ZvpXTAc/PHofP cumrqdbgdLaPbXNX6sUN4cXcqjzvhj2/g9dbp/6c3nEg2jywAqRjjBwwwdedkIkRnSg== 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=FS0reEBF; 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 77F8D606A330 for ; Sat, 14 Nov 2026 04:32:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=FS0reEBF Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8F5011F000C4; Sat, 14 Nov 2026 04:32:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794630761; bh=rUDtpGvWiJFYHdFOYuGZNchwlTnQhy0ujviPe6R/iX8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=FS0reEBFrBXarmzVlAs8fpi0rMB2fYWQ1cvahGT2H2r/XK8RSkkrUZcBdqk1yygo9 bxz4kGLUQvycaOQJoaz8p3CCCZoQ+6VWBz/VOVxDEKOQkbi8qB+0BK4VITmmj9HMPY eavYtGAVR45d2Oon1qE8TMY9VC3bY8F0fsq0vYYIKt7e37XXu0ASgLC2y63s/5Yr2J 5R2jZiRYkG59Cr+t7xBdU178xz+PhgAaUgJHGit1SppfCcuk23XEgmlg8PQ82x1Eok ehdIbneXBfpKFKyqwR7UziXV86HlTyv+sLJ399h+yhrClUcJab2G9/3LgB2C4k4Gx5 0YiZuHz7lKPuQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Chris Mason , "Christian Brauner (Amutable)" , Sasha Levin Subject: [PATCH 5.10.y] aio: fix NULL deref when a fault races ring truncation Date: Fri, 13 Nov 2026 23:32:39 -0500 Message-ID: <20261114042622.2837414-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107063059-failed-5.10-d53b5aa5cfae@kernel.org> References: <20261107063059-failed-5.10-d53b5aa5cfae@kernel.org> 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 Content-Transfer-Encoding: 8bit From: Chris Mason [ Upstream commit d53b5aa5cfae27e4d236fc0ab9581085d27f7d33 ] The aio ring lives in a file on the aio pseudo filesystem and the ring VMA uses filemap_fault(). aio_ctx_aops doesn't have a ->read_folio because aio_setup_ring() puts all folios of the ring into the page cache. So a fault on the ring only works as long as it finds its folio in the page cache. If it doesn't, filemap_fault() calls ->read_folio without checking and we jump to NULL. We already fixed this twice this year. A forked child could inherit the ring mapping, fixed by commit c03ce4173c7b ("fs: aio: set VMA_DONTCOPY_BIT in mmap to fix NULL-pointer-dereference error"). And a partial mremap() could leave part of the ring mapped, fixed by commit 3adf7ae18bf4 ("fs: aio: reject partial mremap to avoid Null-pointer-dereference error"). Both times a VMA outlived the ring and the ring file was truncated under it. There's a third way to get there. kill_ioctx() and the error path of ioctx_alloc() unmap the ring with vm_munmap() and ignore the return value. If vm_munmap() has to wait for mmap_lock and a fatal signal is pending it returns -EINTR and the VMA stays. free_ioctx() then calls put_aio_ring_file() which truncates the ring file to zero. A fault that passed the i_size check in filemap_fault() before that doesn't find its folio anymore, allocates a new one and calls ->read_folio: fault on the ring io_destroy() with SIGKILL pending ================= ================================= vm_munmap() returns -EINTR filemap_fault() i_size check passes free_ioctx() put_aio_ring_file() truncate_setsize(inode, 0) no folio, allocate a new one filemap_read_folio() ->read_folio == NULL All that's needed is a second process that shares the mm. If a CLONE_VM child calls io_destroy() and gets SIGKILLed while it waits for mmap_lock the ring stays mapped for the threads of the parent. Any user can do that. Instead of plugging the routes one by one give the ring a ->read_folio that unlocks the folio and returns -EIO. All folios of a live ring are in the page cache so a fault can only end up there if the ring was truncated. The fault now gets SIGBUS. Nothing else reads the ring file and the aio filesystem uses noop_backing_dev_info so there's no readahead either. Making vm_munmap() unkillable in those two places would only close this one route and bring back what commit ae7987835643 ("mm: make vm_munmap killable") fixed. Fixes: 36bc08cc0170 ("fs/aio: Add support to aio ring pages migration") Cc: stable@vger.kernel.org Signed-off-by: Chris Mason Link: https://patch.msgid.link/20261029-work-fs-ai-fixes-v1-1-88f22792f6f7@kernel.org Signed-off-by: Christian Brauner (Amutable) [ sashal: adapted the folio-based read_folio callback to page-based readpage using unlock_page() ] Signed-off-by: Sasha Levin --- fs/aio.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/fs/aio.c b/fs/aio.c index 16ceed755b7e5..8ba65b4ec8fc2 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -455,7 +455,18 @@ static int aio_migratepage(struct address_space *mapping, struct page *new, } #endif +/* + * filemap_fault() reads a page that it did not find in the page cache. All + * pages of a live ring are there, so the ring was truncated under the fault. + */ +static int aio_readpage(struct file *file, struct page *page) +{ + unlock_page(page); + return -EIO; +} + static const struct address_space_operations aio_ctx_aops = { + .readpage = aio_readpage, .set_page_dirty = __set_page_dirty_no_writeback, #if IS_ENABLED(CONFIG_MIGRATION) .migratepage = aio_migratepage, -- 2.53.0