zram: fix null dereference of handle

In testing I found handle passed to zs_map_object in __zram_bvec_read is
NULL so eh kernel goes oops in pin_object().

The reason is there is no routine to check the slot's freeing after
getting the slot's lock.  This patch fixes it.

[minchan@kernel.org: v2]
  Link: http://lkml.kernel.org/r/1505887347-10881-1-git-send-email-minchan@kernel.org
Link: http://lkml.kernel.org/r/1505788488-26723-1-git-send-email-minchan@kernel.org
Fixes: 1f7319c74275 ("zram: partial IO refactoring")
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 24 deletions

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 2981c27d3aae..f149d3e61234 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -766,27 +766,6 @@ static void zram_slot_unlock(struct zram *zram, u32 index)
         bit_spin_unlock(ZRAM_ACCESS, &zram->table[index].value);
 }
 
-static bool zram_same_page_read(struct zram *zram, u32 index,
-                                struct page *page,
-                                unsigned int offset, unsigned int len)
-{
-        zram_slot_lock(zram, index);
-        if (unlikely(!zram_get_handle(zram, index) ||
-                        zram_test_flag(zram, index, ZRAM_SAME))) {
-                void *mem;
-
-                zram_slot_unlock(zram, index);
-                mem = kmap_atomic(page);
-                zram_fill_page(mem + offset, len,
-                                        zram_get_element(zram, index));
-                kunmap_atomic(mem);
-                return true;
-        }
-        zram_slot_unlock(zram, index);
-
-        return false;
-}
-
 static void zram_meta_free(struct zram *zram, u64 disksize)
 {
         size_t num_pages = disksize >> PAGE_SHIFT;
@@ -884,11 +863,20 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
                 zram_slot_unlock(zram, index);
         }
 
-        if (zram_same_page_read(zram, index, page, 0, PAGE_SIZE))
-                return 0;
-
         zram_slot_lock(zram, index);
         handle = zram_get_handle(zram, index);
+        if (!handle || zram_test_flag(zram, index, ZRAM_SAME)) {
+                unsigned long value;
+                void *mem;
+
+                value = handle ? zram_get_element(zram, index) : 0;
+                mem = kmap_atomic(page);
+                zram_fill_page(mem, PAGE_SIZE, value);
+                kunmap_atomic(mem);
+                zram_slot_unlock(zram, index);
+                return 0;
+        }
+
         size = zram_get_obj_size(zram, index);
 
         src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);