From 90e823498881fb8a91d83e9a8eed87c8c3ff2176 Mon Sep 17 00:00:00 2001 From: Chengming Zhou Date: Mon, 13 May 2024 11:07:56 +0800 Subject: [PATCH] mm/ksm: fix possible UAF of stable_node The commit 2c653d0ee2ae ("ksm: introduce ksm_max_page_sharing per page deduplication limit") introduced a possible failure case in the stable_tree_insert(), where we may free the new allocated stable_node_dup if we fail to prepare the missing chain node. Then that kfolio return and unlock with a freed stable_node set... And any MM activities can come in to access kfolio->mapping, so UAF. Fix it by moving folio_set_stable_node() to the end after stable_node is inserted successfully. Link: https://lkml.kernel.org/r/20240513-b4-ksm-stable-node-uaf-v1-1-f687de76f452@linux.dev Fixes: 2c653d0ee2ae ("ksm: introduce ksm_max_page_sharing per page deduplication limit") Signed-off-by: Chengming Zhou Acked-by: David Hildenbrand Cc: Andrea Arcangeli Cc: Hugh Dickins Cc: Stefan Roesch Signed-off-by: Andrew Morton --- mm/ksm.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/ksm.c b/mm/ksm.c index f5138f43f0d2..452ac8346e6e 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -2153,7 +2153,6 @@ static struct ksm_stable_node *stable_tree_insert(struct folio *kfolio) INIT_HLIST_HEAD(&stable_node_dup->hlist); stable_node_dup->kpfn = kpfn; - folio_set_stable_node(kfolio, stable_node_dup); stable_node_dup->rmap_hlist_len = 0; DO_NUMA(stable_node_dup->nid = nid); if (!need_chain) { @@ -2172,6 +2171,8 @@ static struct ksm_stable_node *stable_tree_insert(struct folio *kfolio) stable_node_chain_add_dup(stable_node_dup, stable_node); } + folio_set_stable_node(kfolio, stable_node_dup); + return stable_node_dup; }