From: Minchan Kim <minchan@xxxxxxxxxx> Subject: 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@xxxxxxxxxx: v2] Link: http://lkml.kernel.org/r/1505887347-10881-1-git-send-email-minchan@xxxxxxxxxx Link: http://lkml.kernel.org/r/1505788488-26723-1-git-send-email-minchan@xxxxxxxxxx Fixes: 1f7319c74275 ("zram: partial IO refactoring") Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- drivers/block/zram/zram_drv.c | 36 ++++++++++---------------------- 1 file changed, 12 insertions(+), 24 deletions(-) diff -puN drivers/block/zram/zram_drv.c~zram-fix-null-dereference-of-handle drivers/block/zram/zram_drv.c --- a/drivers/block/zram/zram_drv.c~zram-fix-null-dereference-of-handle +++ a/drivers/block/zram/zram_drv.c @@ -766,27 +766,6 @@ static void zram_slot_unlock(struct zram 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_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); _