fs: do not update freeing inode i_io_list

After commit cbfecb92 ("fs: record I_DIRTY_TIME even if inode
already has I_DIRTY_INODE") writeback_single_inode can push inode with
I_DIRTY_TIME set to b_dirty_time list. In case of freeing inode with
I_DIRTY_TIME set this can happen after deletion of inode from i_io_list
at evict. Stack trace is following.

evict
fat_evict_inode
fat_truncate_blocks
fat_flush_inodes
writeback_inode
sync_inode_metadata(inode, sync=0)
writeback_single_inode(inode, wbc) <- wbc->sync_mode == WB_SYNC_NONE

This will lead to use after free in flusher thread.

Similar issue can be triggered if writeback_single_inode in the
stack trace update inode->i_io_list. Add explicit check to avoid it.

Fixes: cbfecb92 ("fs: record I_DIRTY_TIME even if inode already has I_DIRTY_INODE")
Reported-by: syzbot+6ba92bd00d5093f7e371@syzkaller.appspotmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Svyatoslav Feldsherov <feldsherov@google.com>
Link: https://lore.kernel.org/r/20221115202001.324188-1-feldsherov@google.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/fs-writeback.c

@@ -1712,9 +1712,14 @@ static int writeback_single_inode(struct inode *inode,
 	wb = inode_to_wb_and_lock_list(inode);
 	spin_lock(&inode->i_lock);
 	/*
-	 * If the inode is now fully clean, then it can be safely removed from
-	 * its writeback list (if any).  Otherwise the flusher threads are
-	 * responsible for the writeback lists.
+	 * If the inode is freeing, its i_io_list shoudn't be updated
+	 * as it can be finally deleted at this moment.
+	 */
+	if (!(inode->i_state & I_FREEING)) {
+		/*
+		 * If the inode is now fully clean, then it can be safely
+		 * removed from its writeback list (if any). Otherwise the
+		 * flusher threads are responsible for the writeback lists.
 		 */
 		if (!(inode->i_state & I_DIRTY_ALL))
 			inode_cgwb_move_to_attached(inode, wb);
@@ -1723,7 +1728,10 @@ static int writeback_single_inode(struct inode *inode,
 				redirty_tail_locked(inode, wb);
 			else if (inode->i_state & I_DIRTY_TIME) {
 				inode->dirtied_when = jiffies;
-			inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
+				inode_io_list_move_locked(inode,
+							  wb,
+							  &wb->b_dirty_time);
+			}
 		}
 	}