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=1794063767; b=R7VKc+KlyDpS49ExBRGXO2KLmrb5m5KRUShoFZBVy0GqQK02fkudgq0XWj8beLlHKBWs KMuQZWz1f1nIWwwaD4TRSxlIHUf26RPerf/DrWYf5FXHk6kcUSwHbezubLm4/3ytEvE/y o9uAPTvGUr5uZS82Wn/COxUdJP+iuSlLR/ldSumyNiOi5nz0EsyMpeenzH6Ejpgyjy4/J wY12sGbqQJe7jmoCMu7x1eT+rUl9W3zQl/6tnQxN/QMkcWuXOZ0nswZ4EnZtfCieczNOr u8Mopg/iBily738xjCAwIQfAEl+qDzLFHJ0P9u10pPYW5Kn96O18jrocSJQKlKkamBw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794063767; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=ERU082DOYUcyc0ZcwNYfFo/FpbL1rwzFH7AZ6vrgA3A=; b=OaTx66cReYOSh/B194rjnZyEXnnXvBzuwINUYsb+PRN3JINSh2m9v4m1t/dX8aHlmTpC HMwr7B/PjpH6cBL7y/o7x7MrprVcJ3A1IKPKVHK5Pk5QBFdP7RQDHR0ZxRyTT+Fg0mHfR s8j+y+DEbkhgRGlsGkFd/WavdDZO9dq8qT2TLH+2YRzZok9SX9kJ47jk9XYbOsjvQ0DED K3tD1UocRtVZh/rbA326feMZomYlTKl5iFltkblEOLkh/EEjRZuQZS+8E9oo1FtCOhuAo 25NquMS0/sR8VxcwX8NBE3o3D+SvZgJYBcUBD6IDprMrc/qFvJ4m3wCQnSJugK4ST3A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=B6osFwVP; 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 2592F608363D; Sat, 7 Nov 2026 15:02:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=B6osFwVP Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9B9C71F008A5; Sat, 7 Nov 2026 15:02:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794063766; bh=ERU082DOYUcyc0ZcwNYfFo/FpbL1rwzFH7AZ6vrgA3A=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=B6osFwVPuLSm060vpd1PahgR0q4g/wAHhr3WrdeUmHZ93VSgNQ8NqzpxwlMQdAH7+ Ue9thMBCcA8FIxFQ82a8cALEvsMqbgz/5GGinJyz8zO8VogEDBj9nsQ6FefbwGWSJP jugwMUeAD+/LJgB0mKwez1vgE+lRoL1cjcgvrInY= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Chris Mason , "Christian Brauner (Amutable)" , Sasha Levin Subject: [PATCH 6.18 859/869] aio: fix NULL deref when a fault races ring truncation Date: Sat, 7 Nov 2026 08:59:01 -0500 Message-ID: <20261107134921.873470084@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261107134852.069646174@linuxfoundation.org> References: <20261107134852.069646174@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore 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 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ 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) 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 bd92bd3e13408..e06fa57b05ca9 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -474,7 +474,18 @@ static int aio_migrate_folio(struct address_space *mapping, struct folio *dst, #define aio_migrate_folio NULL #endif +/* + * filemap_fault() reads a folio that it did not find in the page cache. All + * folios of a live ring are there, so the ring was truncated under the fault. + */ +static int aio_read_folio(struct file *file, struct folio *folio) +{ + folio_unlock(folio); + return -EIO; +} + static const struct address_space_operations aio_ctx_aops = { + .read_folio = aio_read_folio, .dirty_folio = noop_dirty_folio, .migrate_folio = aio_migrate_folio, }; -- 2.53.0