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=1794591200; b=Ca41oRVO92sOkMMETEyPDUdE2Tfl7O+h86aO0GRMpuxPC8TVRW0atqZUrC6WCbFFS9aT XFdue0Kqks7GRH/ZrmTjSx+wWW5g/55BHX/xzoPzhYUUgVnJIL++jmJz+6EDyqM6CtRSL 90IDapX2FSFssI+w8zXy41p1b7lMNaaP/zHE9MV418vVUpXbo5Wk/tnH8lJhvtunTOeTc iIjOXm0JhFF9kfHgblHpFZm3+oWKWIUwU2Q070qR1m+DB6fYzBuhEXeN3Mfyjwg9auJwj ZDdyfXJL5bV/CktNkXFZdA9IRxn6MXEmQeBnjiCTM0S9VpouT47k8qO2aoBSD6dD32A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794591200; 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=/9LRzHag030ieuZoaed1biRZkHVrxxbYNu+JGkyHN0Y=; b=uw9IY4CrX71fug9d5FPbKyeDmxMeVz9AUTxVO2oUkhG1DjWrPoRTeyo8dMoHdhMAdiNX 1Lw2j6Hdck5zCgFfEichWTuSZo4x0Q6Fdy2OKvdjlQkFDckfvyhf2PlKwfzo65YT6xg93 Y1GQmkOmA7Ozah7fS4GDSqrjsbub2tuw3o9LpQYUMP2/9isdV9fKRGiuCKKamNw5WAjs6 fr1F9mZBRZJN5Y73ZfSmsIOcWS9KOdXro08/IoJaktVdM0A14HRblT+TlWsLUfvVKQlxU zrRneo88tMpubdH9xdgY2M34QhgCTzWyfdvXoR4puMXHn629Vs5nAfBc8sff0jwSmHg== 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="AcPegJ/1"; 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 078CA6075851; Fri, 13 Nov 2026 17:33:20 +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=AcPegJ/1 Received: by smtp.kernel.org (Postfix) with ESMTPSA id ADE151F000C4; Fri, 13 Nov 2026 17:33:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794591199; bh=/9LRzHag030ieuZoaed1biRZkHVrxxbYNu+JGkyHN0Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=AcPegJ/1ZHJyIoq8OuzUa3dmRIWNTWzD2cKJApMKdJCkvbBbyV8IkP305gu/dZSqR bxUArFJjlTxGg1FZi2WxwFesslZ3sEAl+qc0n1CYOWr8lwv+9vpKal9G5ANZhtPXdh C4jufMzBgQQv3dbNs6XsgnFaB9OP6gN+4vuUWRfM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Josef Bacik , "Lorenzo Stoakes (ARM)" , Pasha Tatashin , Muhammad Usama Anjum , Xu Xin , "David Hildenbrand (Arm)" , Sasha Levin Subject: [PATCH 6.12 333/670] mm/ksm: reset the unstable trees of all nodes Date: Fri, 13 Nov 2026 10:48:17 -0500 Message-ID: <20261113153823.154448296@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153811.177190860@linuxfoundation.org> References: <20261113153811.177190860@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 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: David Hildenbrand (Arm) [ Upstream commit 890e118e95bfc2aae4432ec2a95192d6f9193211 ] Each full scan resets ksm_nr_node_ids unstable tree roots. Enabling merge_across_nodes resets this count to 1, even if per-node roots were previously allocated. So when toggling "merge_across_nodes" 0 -> 1 -> 0, a scan that starts while the setting is 1 and continues after switching back to 0 can encounter stale unstable tree roots, resulting in UAF. Only root is allowed to change "merge_across_nodes", and the documented sequence is: "merge_across_nodes setting can be changed only when there are no ksm shared pages in the system: set run 2 to unmerge pages first, then to 1 after changing merge_across_nodes, to remerge according to the new setting." Let's fix it by tracking in ksm_nr_node_ids the actual number of allocated tree roots. remove_all_stable_nodes() and ksm_check_stable_tree() will now scan more tree roots (skipping the empty ones), which is harmless. Fixes: ef53d16cded7 ("ksm: allocate roots when needed") Cc: stable@vger.kernel.org Reported-by: Josef Bacik Acked-by: Lorenzo Stoakes (ARM) Reviewed-by: Pasha Tatashin Tested-by: Muhammad Usama Anjum Link: https://patch.msgid.link/20261031-fixes_core-v3-39-d6437171ecc3@kernel.org Reviewed-by: Xu Xin Signed-off-by: David Hildenbrand (Arm) Signed-off-by: Sasha Levin --- mm/ksm.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index aba53b4a3b978..8ce4cd5a382ce 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -470,6 +470,7 @@ static void advisor_stop_scan(void) #ifdef CONFIG_NUMA /* Zeroed when merging across nodes is not allowed */ static unsigned int ksm_merge_across_nodes = 1; +/* Number of allocated stable and unstable tree roots. */ static int ksm_nr_node_ids = 1; #else #define ksm_merge_across_nodes 1U @@ -3532,14 +3533,13 @@ static ssize_t merge_across_nodes_store(struct kobject *kobj, else { root_stable_tree = buf; root_unstable_tree = buf + nr_node_ids; + ksm_nr_node_ids = nr_node_ids; /* Stable tree is empty but not the unstable */ root_unstable_tree[0] = one_unstable_tree[0]; } } - if (!err) { + if (!err) ksm_merge_across_nodes = knob; - ksm_nr_node_ids = knob ? 1 : nr_node_ids; - } } mutex_unlock(&ksm_thread_mutex); -- 2.53.0