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 F35DE349CFC; Wed, 13 May 2026 02:52:47 +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=1778640768; cv=none; b=gZ5PaJA8x9QcIIa6FHM155nmZmtaafrIEl6/Gooreg4N/3zx+tZVfS5L7fn6dlY5qeXX5ZeU9Y+tGlAYr5Nk80EwUyAUjb3ABX8xecLR9zVQMei+MKPd1M5SL8pYhUv4imdIgTEzmDC23qaGXIolxbGydNiBJXhjCD6m3eSleuI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778640768; c=relaxed/simple; bh=3hDimKE1fAKscOhJHZokQog4qjU3uAU1wJQQEOH5qKE=; h=Date:To:From:Subject:Message-Id; b=qThLtJwIO0E7REjC0CoJ58UCVt7X/Dv2p71UgeHaURZEt8yMoCxXQg22alYnxZqvzNQRRFTDNQFjk93q3JS9+F5qkbViupd7RX8S8cxHZzk5Zioxbn05XbF1d7xzTKpoB1cL3/MeObffI3FlIAhHZKHYYZzmVMJostntch5FQRQ= 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=mJYFc58W; 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="mJYFc58W" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 60F91C2BCB0; Wed, 13 May 2026 02:52:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1778640767; bh=3hDimKE1fAKscOhJHZokQog4qjU3uAU1wJQQEOH5qKE=; h=Date:To:From:Subject:From; b=mJYFc58WqK2xliPZbi3IVRbt335npuyJ4eUCN8f+8flCWZ/6IjGZaGkOnmkh6FtlH DVYqu3iN9hbfgbSWZPyGC4KwT8JZrqj7NGluAKcuFTkZCHU68XUl91HwcEcHiComzJ 7cqZ1WotGlw2U6Pu14kRToYTl5TQljh6k4MtB5ns= Date: Tue, 12 May 2026 19:52:46 -0700 To: mm-commits@vger.kernel.org,stable@vger.kernel.org,shakeel.butt@linux.dev,ryncsn@gmail.com,roman.gushchin@linux.dev,muchun.song@linux.dev,mhocko@kernel.org,hughd@google.com,hannes@cmpxchg.org,david@kernel.org,baohua@kernel.org,jose.fernandez@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-swap_cgroup-fix-null-deref-in-lookup_swap_cgroup_id-on-swapless-host.patch added to mm-hotfixes-unstable branch Message-Id: <20260513025247.60F91C2BCB0@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm: swap_cgroup: fix NULL deref in lookup_swap_cgroup_id on swapless host has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-swap_cgroup-fix-null-deref-in-lookup_swap_cgroup_id-on-swapless-host.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap_cgroup-fix-null-deref-in-lookup_swap_cgroup_id-on-swapless-host.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 various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: "Jose Fernandez (Anthropic)" Subject: mm: swap_cgroup: fix NULL deref in lookup_swap_cgroup_id on swapless host Date: Mon, 04 May 2026 12:55:17 +0000 lookup_swap_cgroup_id() passes swap_cgroup_ctrl[type].map to __swap_cgroup_id_lookup() without checking that the type was ever registered via swap_cgroup_swapon(). On a swapless host every ctrl->map is NULL, so __swap_cgroup_id_lookup() dereferences NULL + a scaled swp_offset(). Since commit bea67dcc5eea ("mm: attempt to batch free swap entries for zap_pte_range()"), zap_pte_range() -> swap_pte_batch() calls lookup_swap_cgroup_id() on any non-present, non-none PTE that decodes as a real swap entry, without first validating it against swap_info[]. A single PTE corrupted into a type-0 swap entry takes the host down at process exit. We hit this in production on a swapless 6.12.58 host: ~1s of "get_swap_device: Bad swap file entry 3f800204222bb" (do_swap_page() being correctly defensive about the same entry) followed by BUG: unable to handle page fault for address: 000003f800204220 RIP: 0010:lookup_swap_cgroup_id+0x2b/0x60 Call Trace: swap_pte_batch+0xbf/0x230 zap_pte_range+0x4c8/0x780 unmap_page_range+0x190/0x3e0 exit_mmap+0xd9/0x3c0 do_exit+0x20c/0x4b0 syzbot has reported the identical stack. The source of the PTE corruption is a separate bug; this change makes the teardown path as robust as the fault path already is. Every other caller of lookup_swap_cgroup_id() is downstream of a get_swap_device() that has already validated the entry, so the new branch is cold. Link: https://lore.kernel.org/20260504-swap-cgroup-fix-7-0-v1-1-f53ff41ee553@linux.dev Fixes: bea67dcc5eea ("mm: attempt to batch free swap entries for zap_pte_range()") Signed-off-by: Jose Fernandez (Anthropic) Reported-by: syzbot+e12bd9ca48157add237a@syzkaller.appspotmail.com Link: https://lore.kernel.org/r/69859728.050a0220.3b3015.0033.GAE@google.com Assisted-by: Claude:unspecified Cc: Barry Song Cc: David Hildenbrand Cc: Hugh Dickins Cc: Johannes Weiner Cc: Kairui Song Cc: Michal Hocko Cc: Muchun Song Cc: Roman Gushchin Cc: Shakeel Butt Cc: Signed-off-by: Andrew Morton --- mm/swap_cgroup.c | 2 ++ 1 file changed, 2 insertions(+) --- a/mm/swap_cgroup.c~mm-swap_cgroup-fix-null-deref-in-lookup_swap_cgroup_id-on-swapless-host +++ a/mm/swap_cgroup.c @@ -124,6 +124,8 @@ unsigned short lookup_swap_cgroup_id(swp return 0; ctrl = &swap_cgroup_ctrl[swp_type(ent)]; + if (unlikely(!ctrl->map)) + return 0; return __swap_cgroup_id_lookup(ctrl->map, swp_offset(ent)); } _ Patches currently in -mm which might be from jose.fernandez@linux.dev are mm-swap_cgroup-fix-null-deref-in-lookup_swap_cgroup_id-on-swapless-host.patch