fuse: Add bad inode check in fuse_destroy_inode()

make_bad_inode() sets inode->i_mode to S_IFREG if I/O error is detected
in fuse_do_getattr()/fuse_do_setattr(). If the inode is not a regular
file, write_files and queued_writes in fuse_inode are not initialized
and have NULL or invalid pointers written by other members in a union.
So, list_empty() returns false in fuse_destroy_inode(). Add
is_bad_inode() to check if make_bad_inode() was called.

Reported-by: syzbot+b9c89b84423073226299@syzkaller.appspotmail.com
Fixes: ab2257e9 ("fuse: reduce size of struct fuse_inode")
Signed-off-by: Myungho Jung <mhjungk@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/inode.c

@@ -115,7 +115,7 @@ static void fuse_i_callback(struct rcu_head *head)
 static void fuse_destroy_inode(struct inode *inode)
 {
 	struct fuse_inode *fi = get_fuse_inode(inode);
-	if (S_ISREG(inode->i_mode)) {
+	if (S_ISREG(inode->i_mode) && !is_bad_inode(inode)) {
 		WARN_ON(!list_empty(&fi->write_files));
 		WARN_ON(!list_empty(&fi->queued_writes));
 	}