From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 57F021CA8F; Mon, 1 Apr 2024 16:05:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711987509; cv=none; b=XO+0bO9UsE15iddjbT63i/U6hVTAfNv2UaxtDcUsuWMRYqIzuxRDOZzV3Z6jZfBbUB5Y0JlKnd+T4REXZO0Q5jlkBoYCREivn0TkZ6Zh17YxX7n6hrBHGGY80FxTHpjJWDgRMsiuoVVwTCASM/0kk1eLgE8cKvdV8vnu4xzsHb8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711987509; c=relaxed/simple; bh=4tMNuuEly6qxZtzq8mm5wjqZQXuU+4BGuoRBgUWkSAs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=e8zRdVhmcZk8KbPCw+gv7Ux8HgFhsN8S9GFo4J0hGhc3qFy/cMdGgLK8rFVSbubpoWXq09axr/jV9CVmJF2no2dR/qYn1k+/or0Xds2fE+bYzZdWEF/LQAUv8392n1wMkm/AUQt02I1BrWmPdgs+1OlJpNV8Jyi8zW6wbqdOllA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=fiGqLFX3; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="fiGqLFX3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7AF4AC433C7; Mon, 1 Apr 2024 16:05:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1711987509; bh=4tMNuuEly6qxZtzq8mm5wjqZQXuU+4BGuoRBgUWkSAs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fiGqLFX3yhVeSCYsq0N0QSI7Efpqe1kzOtvdjVhCiFAaT4mnxUyaZ+Heiiyz3/Caj cKSCjHwpBYrEsGe2aV8VRJPbrC4t2t0wnjaO4wpPDHXB2yuik7lrG0gl0mOLQ8beqa uqsASfotjPTXopqc0kEog21UTpcrVsKLZypGzbBg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Johannes Weiner , Chengming Zhou , Nhat Pham , Andrew Morton , Jann Horn Subject: [PATCH 6.8 309/399] mm: cachestat: fix two shmem bugs Date: Mon, 1 Apr 2024 17:44:35 +0200 Message-ID: <20240401152558.411370553@linuxfoundation.org> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240401152549.131030308@linuxfoundation.org> References: <20240401152549.131030308@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.8-stable review patch. If anyone has any objections, please let me know. ------------------ From: Johannes Weiner commit d5d39c707a4cf0bcc84680178677b97aa2cb2627 upstream. When cachestat on shmem races with swapping and invalidation, there are two possible bugs: 1) A swapin error can have resulted in a poisoned swap entry in the shmem inode's xarray. Calling get_shadow_from_swap_cache() on it will result in an out-of-bounds access to swapper_spaces[]. Validate the entry with non_swap_entry() before going further. 2) When we find a valid swap entry in the shmem's inode, the shadow entry in the swapcache might not exist yet: swap IO is still in progress and we're before __remove_mapping; swapin, invalidation, or swapoff have removed the shadow from swapcache after we saw the shmem swap entry. This will send a NULL to workingset_test_recent(). The latter purely operates on pointer bits, so it won't crash - node 0, memcg ID 0, eviction timestamp 0, etc. are all valid inputs - but it's a bogus test. In theory that could result in a false "recently evicted" count. Such a false positive wouldn't be the end of the world. But for code clarity and (future) robustness, be explicit about this case. Bail on get_shadow_from_swap_cache() returning NULL. Link: https://lkml.kernel.org/r/20240315095556.GC581298@cmpxchg.org Fixes: cf264e1329fb ("cachestat: implement cachestat syscall") Signed-off-by: Johannes Weiner Reported-by: Chengming Zhou [Bug #1] Reported-by: Jann Horn [Bug #2] Reviewed-by: Chengming Zhou Reviewed-by: Nhat Pham Cc: [v6.5+] Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/filemap.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) --- a/mm/filemap.c +++ b/mm/filemap.c @@ -4153,7 +4153,23 @@ static void filemap_cachestat(struct add /* shmem file - in swap cache */ swp_entry_t swp = radix_to_swp_entry(folio); + /* swapin error results in poisoned entry */ + if (non_swap_entry(swp)) + goto resched; + + /* + * Getting a swap entry from the shmem + * inode means we beat + * shmem_unuse(). rcu_read_lock() + * ensures swapoff waits for us before + * freeing the swapper space. However, + * we can race with swapping and + * invalidation, so there might not be + * a shadow in the swapcache (yet). + */ shadow = get_shadow_from_swap_cache(swp); + if (!shadow) + goto resched; } #endif if (workingset_test_recent(shadow, true, &workingset))