dm thin metadata: Fix use-after-free in dm_bm_set_read_only

The following error ocurred when testing disk online/offline:

[  301.798344] device-mapper: thin: 253:5: aborting current metadata transaction
[  301.848441] device-mapper: thin: 253:5: failed to abort metadata transaction
[  301.849206] Aborting journal on device dm-26-8.
[  301.850489] EXT4-fs error (device dm-26) in __ext4_new_inode:943: Journal has aborted
[  301.851095] EXT4-fs (dm-26): Delayed block allocation failed for inode 398742 at logical offset 181 with max blocks 19 with error 30
[  301.854476] BUG: KASAN: use-after-free in dm_bm_set_read_only+0x3a/0x40 [dm_persistent_data]

Reason is:

 metadata_operation_failed
    abort_transaction
        dm_pool_abort_metadata
	    __create_persistent_data_objects
	        r = __open_or_format_metadata
	        if (r) --> If failed will free pmd->bm but pmd->bm not set NULL
		    dm_block_manager_destroy(pmd->bm);
    set_pool_mode
	dm_pool_metadata_read_only(pool->pmd);
	dm_bm_set_read_only(pmd->bm);  --> use-after-free

Add checks to see if pmd->bm is NULL in dm_bm_set_read_only and
dm_bm_set_read_write functions.  If bm is NULL it means creating the
bm failed and so dm_bm_is_read_only must return true.
Signed-off-by: Ye Bin <yebin10@huawei.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-thin-metadata.c

@@ -958,7 +958,7 @@ int dm_pool_metadata_close(struct dm_pool_metadata *pmd)
 	}
 
 	pmd_write_lock_in_core(pmd);
-	if (!dm_bm_is_read_only(pmd->bm) && !pmd->fail_io) {
+	if (!pmd->fail_io && !dm_bm_is_read_only(pmd->bm)) {
 		r = __commit_transaction(pmd);
 		if (r < 0)
 			DMWARN("%s: __commit_transaction() failed, error = %d",

drivers/md/persistent-data/dm-block-manager.c

@@ -493,7 +493,7 @@ int dm_bm_write_lock(struct dm_block_manager *bm,
 	void *p;
 	int r;
 
-	if (bm->read_only)
+	if (dm_bm_is_read_only(bm))
 		return -EPERM;
 
 	p = dm_bufio_read(bm->bufio, b, (struct dm_buffer **) result);
@@ -562,7 +562,7 @@ int dm_bm_write_lock_zero(struct dm_block_manager *bm,
 	struct buffer_aux *aux;
 	void *p;
 
-	if (bm->read_only)
+	if (dm_bm_is_read_only(bm))
 		return -EPERM;
 
 	p = dm_bufio_new(bm->bufio, b, (struct dm_buffer **) result);
@@ -602,7 +602,7 @@ EXPORT_SYMBOL_GPL(dm_bm_unlock);
 
 int dm_bm_flush(struct dm_block_manager *bm)
 {
-	if (bm->read_only)
+	if (dm_bm_is_read_only(bm))
 		return -EPERM;
 
 	return dm_bufio_write_dirty_buffers(bm->bufio);
@@ -616,19 +616,21 @@ void dm_bm_prefetch(struct dm_block_manager *bm, dm_block_t b)
 
 bool dm_bm_is_read_only(struct dm_block_manager *bm)
 {
-	return bm->read_only;
+	return (bm ? bm->read_only : true);
 }
 EXPORT_SYMBOL_GPL(dm_bm_is_read_only);
 
 void dm_bm_set_read_only(struct dm_block_manager *bm)
 {
-	bm->read_only = true;
+	if (bm)
+		bm->read_only = true;
 }
 EXPORT_SYMBOL_GPL(dm_bm_set_read_only);
 
 void dm_bm_set_read_write(struct dm_block_manager *bm)
 {
-	bm->read_only = false;
+	if (bm)
+		bm->read_only = false;
 }
 EXPORT_SYMBOL_GPL(dm_bm_set_read_write);