[PATCH v4] mm: workingset: fix NULL ptr dereference

[Minchan Kim]

GFP mask passed to page cache functions (often coming from
mapping->gfp_mask) is used both for allocation of page cache page and for
allocation of radix tree metadata necessary to add the page to the page
cache. When the mask contains __GFP_ZERO (as is the case for some f2fs
metadata mappings), this breaks radix tree code as that code expects
allocated radix tree nodes to be properly initialized by the slab
constructor and not zeroed. In particular node->private_list is failing
list_empty() check and the following list operation in
workingset_update_node() will dereference NULL.

Fix the problem by removing non-reclimable flags by GFP_RECLAIM_MASK
for radix tree allocations.

Fixes: 449dd6984d0e ("mm: keep page cache radix tree nodes in check")
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Cc: Chao Yu <yuchao0@xxxxxxxxxx>
Cc: Christopher Lameter <cl@xxxxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Reported-by: Chris Fries <cfries@xxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
 mm/filemap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index ab77e19ab09c..5f3311edfea4 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -786,7 +786,7 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
 	VM_BUG_ON_PAGE(!PageLocked(new), new);
 	VM_BUG_ON_PAGE(new->mapping, new);
 
-	error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
+	error = radix_tree_preload(gfp_mask & GFP_RECLAIM_MASK);
 	if (!error) {
 		struct address_space *mapping = old->mapping;
 		void (*freepage)(struct page *);
@@ -842,7 +842,7 @@ static int __add_to_page_cache_locked(struct page *page,
 			return error;
 	}
 
-	error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
+	error = radix_tree_maybe_preload(gfp_mask & GFP_RECLAIM_MASK);
 	if (error) {
 		if (!huge)
 			mem_cgroup_cancel_charge(page, memcg, false);
-- 
2.17.0.484.g0c8726318c-goog