linux-kernel - [PATCH 3.16 182/366] mm/filemap.c: fix NULL pointer in page_cache_tree

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Message-ID: <lsq.1539530741.923997029@decadent.org.uk>
Date:   Sun, 14 Oct 2018 16:25:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Matthew Wilcox" <mawilcox@...rosoft.com>,
        "Chris Fries" <cfries@...gle.com>,
        "Michal Hocko" <mhocko@...e.com>, "Jan Kara" <jack@...e.cz>,
        "Johannes Weiner" <hannes@...xchg.org>
Subject: [PATCH 3.16 182/366] mm/filemap.c: fix NULL pointer in
 page_cache_tree_insert()

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Matthew Wilcox <mawilcox@...rosoft.com>

commit abc1be13fd113ddef5e2d807a466286b864caed3 upstream.

f2fs specifies the __GFP_ZERO flag for allocating some of its pages.
Unfortunately, the page cache also uses the mapping's GFP flags for
allocating radix tree nodes.  It always masked off the __GFP_HIGHMEM
flag, and masks off __GFP_ZERO in some paths, but not all.  That causes
radix tree nodes to be allocated with a NULL list_head, which causes
backtraces like:

  __list_del_entry+0x30/0xd0
  list_lru_del+0xac/0x1ac
  page_cache_tree_insert+0xd8/0x110

The __GFP_DMA and __GFP_DMA32 flags would also be able to sneak through
if they are ever used.  Fix them all by using GFP_RECLAIM_MASK at the
innermost location, and remove it from earlier in the callchain.

Link: http://lkml.kernel.org/r/20180411060320.14458-2-willy@infradead.org
Fixes: 449dd6984d0e ("mm: keep page cache radix tree nodes in check")
Signed-off-by: Matthew Wilcox <mawilcox@...rosoft.com>
Reported-by: Chris Fries <cfries@...gle.com>
Debugged-by: Minchan Kim <minchan@...nel.org>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Acked-by: Michal Hocko <mhocko@...e.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
[bwh: Backported to 3.16:
 - Drop change in page_cache_read(), which always passes GFP_KERNEL
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -529,7 +529,7 @@ int replace_page_cache_page(struct page
 	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 *);
@@ -576,7 +576,7 @@ static int __add_to_page_cache_locked(st
 	if (error)
 		return error;
 
-	error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
+	error = radix_tree_maybe_preload(gfp_mask & GFP_RECLAIM_MASK);
 	if (error) {
 		mem_cgroup_uncharge_cache_page(page);
 		return error;
@@ -1111,8 +1111,7 @@ no_page:
 		if (fgp_flags & FGP_ACCESSED)
 			init_page_accessed(page);
 
-		err = add_to_page_cache_lru(page, mapping, offset,
-				gfp_mask & GFP_RECLAIM_MASK);
+		err = add_to_page_cache_lru(page, mapping, offset, gfp_mask);
 		if (unlikely(err)) {
 			page_cache_release(page);
 			page = NULL;