dm thin metadata: check fail_io before using data_sm

Must check pmd->fail_io before using pmd->data_sm since
pmd->data_sm may be destroyed by other processes.

       P1(kworker)                             P2(message)
do_worker
 process_prepared
  process_prepared_discard_passdown_pt2
   dm_pool_dec_data_range
                                    pool_message
                                     commit
                                      dm_pool_commit_metadata
                                        ↓
                                       // commit failed
                                      metadata_operation_failed
                                       abort_transaction
                                        dm_pool_abort_metadata
                                         __open_or_format_metadata
                                           ↓
                                          dm_sm_disk_open
                                            ↓
                                           // open failed
                                           // pmd->data_sm is NULL
    dm_sm_dec_blocks
      ↓
     // try to access pmd->data_sm --> UAF

As shown above, if dm_pool_commit_metadata() and
dm_pool_abort_metadata() fail in pool_message process, kworker may
trigger UAF.

Fixes: be500ed ("dm space maps: improve performance with inc/dec on ranges of blocks")
Cc: [email protected]
Signed-off-by: Li Lingfeng <[email protected]>
Signed-off-by: Mike Snitzer <[email protected]>

drivers/md/dm-thin-metadata.c

@@ -1756,35 +1756,39 @@ int dm_thin_remove_range(struct dm_thin_device *td,
 
 int dm_pool_block_is_shared(struct dm_pool_metadata *pmd, dm_block_t b, bool *result)
 {
-	int r;
+	int r = -EINVAL;
 	uint32_t ref_count;
 
 	down_read(&pmd->root_lock);
-	r = dm_sm_get_count(pmd->data_sm, b, &ref_count);
-	if (!r)
-		*result = (ref_count > 1);
+	if (!pmd->fail_io) {
+		r = dm_sm_get_count(pmd->data_sm, b, &ref_count);
+		if (!r)
+			*result = (ref_count > 1);
+	}
 	up_read(&pmd->root_lock);
 
 	return r;
 }
 
 int dm_pool_inc_data_range(struct dm_pool_metadata *pmd, dm_block_t b, dm_block_t e)
 {
-	int r = 0;
+	int r = -EINVAL;
 
 	pmd_write_lock(pmd);
-	r = dm_sm_inc_blocks(pmd->data_sm, b, e);
+	if (!pmd->fail_io)
+		r = dm_sm_inc_blocks(pmd->data_sm, b, e);
 	pmd_write_unlock(pmd);
 
 	return r;
 }
 
 int dm_pool_dec_data_range(struct dm_pool_metadata *pmd, dm_block_t b, dm_block_t e)
 {
-	int r = 0;
+	int r = -EINVAL;
 
 	pmd_write_lock(pmd);
-	r = dm_sm_dec_blocks(pmd->data_sm, b, e);
+	if (!pmd->fail_io)
+		r = dm_sm_dec_blocks(pmd->data_sm, b, e);
 	pmd_write_unlock(pmd);
 
 	return r;