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=1794590423; b=o+EJ6EMa8wfsO5CCICX4vuk2Toxn+zasYwk+uty/ij+t4I/xQvqk68hr2dO0HFLDoS6x eNELEoK2CeB2cFnbRPVBqSq1fL6Re2Ap6BPC4/cWqCMaFbkP0NUZVNN6FNPgfAAE1S4qC wfiiyd0aNIDAQJnWU9eJeEIyjnYvQ9Ivt3VaEkES5BkFYWGcImMdIysoHLLQc3BEpi3XU TUq6Ig+N72goFal/1VK9qfXwLzjez/Rc2ehNm/ewv1LOqXRqhBoWsSwuVzn/wy7mNP/lQ 2oiCjPsuCVC35tKOh7Ra/JVHzHOJ5rU7Jc7ZaiMtqYWTkZUo27bpbxTYVfhYTIktiCw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794590423; 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=Y06n98cQdBZN6XS2w43AmD5VcM40XlkndDtBBv5Z8Y0=; b=Ia7s5beyK0EhEZgKwxza2Le10h9AOporfLfQzFMMXIjW9I1Xs2lSrdORwHLQdqXDWP6J skvSUfnWHSQZdje8zxlb1iPTOicJKVEfYgr7xv2hXWD8BXZSTXWgjkKtHdMYH5GvBO50j QHWXPnbaEkXozXaJNyZE5f31EgOAmYtxgJoozWnUIehY+nT/QlggbZ7Bw/Ph4T7W3LSKB b/XgJrFFAzsik8gHHhbCVNhcvMfv6QPySX9phMTM4FUe0S8hjFfuIlHpVTZew9L/4yIDz X1eXxUCxnkY2blR9ZipMzVOYQejduFFsuPwRNP+YcfR9ZoeC8PUKnmR9g+SB9ltOerw== 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=vtlA9U8x; 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 123F2606B46E; Fri, 13 Nov 2026 17:20:23 +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=vtlA9U8x Received: by smtp.kernel.org (Postfix) with ESMTPSA id B79A91F000C7; Fri, 13 Nov 2026 17:20:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794590422; bh=Y06n98cQdBZN6XS2w43AmD5VcM40XlkndDtBBv5Z8Y0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=vtlA9U8xxs6RYStCCQ+wO+CgDJd+ziQR9Z1P3yjqN27bc3Tk1oaF0+E6xB+DiOO5t L2UVJmtEArL1E817mSAFi7Lh83pJi5G1eWxTxZayDkr8bTxQqPCgGXn0WJB9mGXawS H17nTL7AvkTr3V9buGtWDLwwLRXfJpb4XLTWViOk= 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 6.18 386/686] mm/ksm: reset the unstable trees of all nodes Date: Fri, 13 Nov 2026 10:48:39 -0500 Message-ID: <20261113153834.074407687@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153820.902362109@linuxfoundation.org> References: <20261113153820.902362109@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-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 1eee363fd727e..bcaca6e99b1ce 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -469,6 +469,7 @@ 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 @@ -3572,14 +3573,13 @@ 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