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 9BC9555C16; Mon, 18 Mar 2024 19:25:15 +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=1710789915; cv=none; b=Qtm+Ax/X9dd3vbyHQuFde/0mqgHtMIfyQnB8jE7T/d2Hf89gOSUnS2eRscKMPSIHzwi/qosKS/ECr1CGihqYHORNhp1/ntBFkYOX3OFs5cHeet9LrEPy9OMtqA7Aiyr6C6Gq9k2kpTqaRP3DXAeQ70KGHulk+V7eCFa1x5FEvAw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710789915; c=relaxed/simple; bh=Av/ON1HOSRbDOn3Trqb+akXjfyDeOtmnnvfxi2FEdyM=; h=Date:To:From:Subject:Message-Id; b=lwDya6uiPW4jj9OcYimglwzLvbekOXvGoKtXbkcla+11O2LZGNiTR5zyAcyj6SupNf25XGluad6tG2kB934toV753D9b9G/uz/rquZijCiIXpBCo9WFVUn+tx20C5wKezqukUR3Vk/K80FxLHoJf18ynjFi0M3E1R56ctSVQynw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=uS5ZK69Q; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="uS5ZK69Q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D76AC433F1; Mon, 18 Mar 2024 19:25:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1710789915; bh=Av/ON1HOSRbDOn3Trqb+akXjfyDeOtmnnvfxi2FEdyM=; h=Date:To:From:Subject:From; b=uS5ZK69Q2Fb5DtXKHnkIy81U72tUWbkB2djyFJOvCUvDjzUkORPcEOlkYpLF6teDY rR6g3GgS1k+Gr4+eOd0fD6ko1H/Euikc6W2adkrfYpyMaxzVh27o1WBAWydSJe0Ast nMwd4NFFxTKPsreArX3KLfrovXbPZGGHl8QhHysE= Date: Mon, 18 Mar 2024 12:25:14 -0700 To: mm-commits@vger.kernel.org,stable@vger.kernel.org,nphamcs@gmail.com,jannh@google.com,chengming.zhou@linux.dev,hannes@cmpxchg.org,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-cachestat-fix-two-shmem-bugs.patch added to mm-hotfixes-unstable branch Message-Id: <20240318192515.4D76AC433F1@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm: cachestat: fix two shmem bugs has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-cachestat-fix-two-shmem-bugs.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-cachestat-fix-two-shmem-bugs.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Johannes Weiner Subject: mm: cachestat: fix two shmem bugs Date: Fri, 15 Mar 2024 05:55:56 -0400 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 --- mm/filemap.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) --- a/mm/filemap.c~mm-cachestat-fix-two-shmem-bugs +++ a/mm/filemap.c @@ -4197,7 +4197,23 @@ 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)) _ Patches currently in -mm which might be from hannes@cmpxchg.org are mm-cachestat-fix-two-shmem-bugs.patch