From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 A14F05A79B; Thu, 16 Jul 2026 14:06:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784210817; cv=none; b=CgK6gYZyG78R8GGCdEeY8kIepFcgF99ubZ1AbthKxEv3+ppDudLy7qYoA/CiuTSiCYLy5BCilcs9SmMrcDjryZbMyNJNgVhoJYbPR+lcG1qh/qyRq7Phs4sBMo2kstvA+K4/T2cMS8sHTlCl7NJB8H+0TJ1KWCxKuA2WPo5oz/o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784210817; c=relaxed/simple; bh=bJt6H6G5gqODvKCsv5hX2NHo/bwfg5372GHN+zUpFEs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=X2AWV5UrII+vkzvOWaiLIsrXRDRQmowoN/6QhwufYuWOm/kKPgfW53Ho8p/XMfhAydRAIelZCueyiU3SHZI3lSWLPgqnxx+zTFjBTOSQw1MY6ZrqLgdVEm0LCyGWFQYmvF+MqarHR1PAEAx3tUN+UJF9gX/mMZ+sFbvgq/EBHow= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=DRneU4N8; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="DRneU4N8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 195701F000E9; Thu, 16 Jul 2026 14:06:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784210815; bh=1UDL7YLcpzS5yXXDiLZ7+T4/pVB2HEQlbvv5Z2T2M2Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=DRneU4N8kLSRrdOLtisNRtiw1mdOw6wc20OleU1Dvh/v85Fh1cBtatkQQtbM/uiXD +HBIvQIGEUnk/O8TYuNnsLQJhcR9MkYRb9GmAgi2cFuC5W0+HzqEh2NR1SWMjdobL6 6sncB8h9Hfys5cM6EV3aoYZpOM7oGxVEwDEu6Iys= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Jose Fernandez (Anthropic)" , syzbot+e12bd9ca48157add237a@syzkaller.appspotmail.com, Barry Song , David Hildenbrand , Hugh Dickins , Johannes Weiner , Kairui Song , Michal Hocko , Muchun Song , Roman Gushchin , Shakeel Butt , Andrew Morton Subject: [PATCH 6.18 192/480] mm: swap_cgroup: fix NULL deref in lookup_swap_cgroup_id on swapless host Date: Thu, 16 Jul 2026 15:28:59 +0200 Message-ID: <20260716133048.881074030@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260716133044.672218725@linuxfoundation.org> References: <20260716133044.672218725@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jose Fernandez (Anthropic) commit 63b02a9409cb5180398491b093e48bcb5315f5fb upstream. 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 Signed-off-by: Greg Kroah-Hartman --- mm/swap_cgroup.c | 2 ++ 1 file changed, 2 insertions(+) --- a/mm/swap_cgroup.c +++ b/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)); }