From: Matthew Wilcox mawilcox@microsoft.com Subject: mm/filemap.c: fix NULL pointer in page_cache_tree_insert()

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:

[<ffffff80086f4de0>] __list_del_entry+0x30/0xd0 [<ffffff8008362018>] list_lru_del+0xac/0x1ac [<ffffff800830f04c>] 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@microsoft.com Reported-by: Chris Fries cfries@google.com Debugged-by: Minchan Kim minchan@kernel.org Acked-by: Johannes Weiner hannes@cmpxchg.org Acked-by: Michal Hocko mhocko@suse.com Reviewed-by: Jan Kara jack@suse.cz Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/filemap.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)

diff -puN mm/filemap.c~fix-null-pointer-in-page_cache_tree_insert mm/filemap.c --- a/mm/filemap.c~fix-null-pointer-in-page_cache_tree_insert +++ a/mm/filemap.c @@ -786,7 +786,7 @@ 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 *); @@ -842,7 +842,7 @@ static int __add_to_page_cache_locked(st 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); @@ -1585,8 +1585,7 @@ no_page: if (fgp_flags & FGP_ACCESSED) __SetPageReferenced(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)) { put_page(page); page = NULL; @@ -2387,7 +2386,7 @@ static int page_cache_read(struct file * if (!page) return -ENOMEM;

- ret = add_to_page_cache_lru(page, mapping, offset, gfp_mask & GFP_KERNEL); + ret = add_to_page_cache_lru(page, mapping, offset, gfp_mask); if (ret == 0) ret = mapping->a_ops->readpage(file, page); else if (ret == -EEXIST) _