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Subject[PATCH] zram: fix null dereference of handle
Date
For the testing, I found handle passed to zs_map_object in __zram_bvec_read
is NULL so that kernel goes the oops by 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.

Fixes: 1f7319c74275 ("zram: partial IO refactoring")
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
drivers/block/zram/zram_drv.c | 34 ++++++++++------------------------
1 file changed, 10 insertions(+), 24 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 91a72df41ab0..23172641fc01 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -758,27 +758,6 @@ 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;
@@ -876,11 +855,18 @@ 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 (unlikely(!handle || zram_test_flag(zram, index, ZRAM_SAME))) {
+ void *mem;
+
+ mem = kmap_atomic(page);
+ zram_fill_page(mem, PAGE_SIZE, zram_get_element(zram, index));
+ 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);
--
2.7.4
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