bcachefs: make RO snapshots actually RO

Add checks to all the VFS paths for "are we in a RO snapshot?".

Note - we don't check this when setting inode options via our xattr
interface, since those generally only affect data placement, not
contents of data.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Reported-by: "Carl E. Thompson" <list-bcachefs@carlthompson.net>

fs/bcachefs/acl.c

@@ -366,7 +366,8 @@ int bch2_set_acl(struct mnt_idmap *idmap,
 	bch2_trans_begin(trans);
 	acl = _acl;
 
-	ret = bch2_inode_peek(trans, &inode_iter, &inode_u, inode_inum(inode),
+	ret   = bch2_subvol_is_ro_trans(trans, inode->ei_subvol) ?:
+		bch2_inode_peek(trans, &inode_iter, &inode_u, inode_inum(inode),
 			      BTREE_ITER_INTENT);
 	if (ret)
 		goto btree_err;

fs/bcachefs/fs-ioctl.c

@@ -100,7 +100,8 @@ static int bch2_ioc_setflags(struct bch_fs *c,
 	}
 
 	mutex_lock(&inode->ei_update_lock);
-	ret = bch2_write_inode(c, inode, bch2_inode_flags_set, &s,
+	ret   = bch2_subvol_is_ro(c, inode->ei_subvol) ?:
+		bch2_write_inode(c, inode, bch2_inode_flags_set, &s,
 			       ATTR_CTIME);
 	mutex_unlock(&inode->ei_update_lock);
 
@@ -183,13 +184,10 @@ static int bch2_ioc_fssetxattr(struct bch_fs *c,
 	}
 
 	mutex_lock(&inode->ei_update_lock);
-	ret = bch2_set_projid(c, inode, fa.fsx_projid);
-	if (ret)
-		goto err_unlock;
-
-	ret = bch2_write_inode(c, inode, fssetxattr_inode_update_fn, &s,
+	ret   = bch2_subvol_is_ro(c, inode->ei_subvol) ?:
+		bch2_set_projid(c, inode, fa.fsx_projid) ?:
+		bch2_write_inode(c, inode, fssetxattr_inode_update_fn, &s,
 			       ATTR_CTIME);
-err_unlock:
 	mutex_unlock(&inode->ei_update_lock);
 err:
 	inode_unlock(&inode->v);

fs/bcachefs/fs.c

@@ -258,7 +258,8 @@ __bch2_create(struct mnt_idmap *idmap,
 retry:
 	bch2_trans_begin(trans);
 
-	ret   = bch2_create_trans(trans,
+	ret   = bch2_subvol_is_ro_trans(trans, dir->ei_subvol) ?:
+		bch2_create_trans(trans,
 				  inode_inum(dir), &dir_u, &inode_u,
 				  !(flags & BCH_CREATE_TMPFILE)
 				  ? &dentry->d_name : NULL,
@@ -430,7 +431,9 @@ static int bch2_link(struct dentry *old_dentry, struct inode *vdir,
 
 	lockdep_assert_held(&inode->v.i_rwsem);
 
-	ret = __bch2_link(c, inode, dir, dentry);
+	ret   = bch2_subvol_is_ro(c, dir->ei_subvol) ?:
+		bch2_subvol_is_ro(c, inode->ei_subvol) ?:
+		__bch2_link(c, inode, dir, dentry);
 	if (unlikely(ret))
 		return ret;
 
@@ -481,7 +484,11 @@ int __bch2_unlink(struct inode *vdir, struct dentry *dentry,
 
 static int bch2_unlink(struct inode *vdir, struct dentry *dentry)
 {
-	return __bch2_unlink(vdir, dentry, false);
+	struct bch_inode_info *dir= to_bch_ei(vdir);
+	struct bch_fs *c = dir->v.i_sb->s_fs_info;
+
+	return bch2_subvol_is_ro(c, dir->ei_subvol) ?:
+		__bch2_unlink(vdir, dentry, false);
 }
 
 static int bch2_symlink(struct mnt_idmap *idmap,
@@ -562,6 +569,11 @@ static int bch2_rename2(struct mnt_idmap *idmap,
 			 src_inode,
 			 dst_inode);
 
+	ret   = bch2_subvol_is_ro_trans(trans, src_dir->ei_subvol) ?:
+		bch2_subvol_is_ro_trans(trans, dst_dir->ei_subvol);
+	if (ret)
+		goto err;
+
 	if (inode_attr_changing(dst_dir, src_inode, Inode_opt_project)) {
 		ret = bch2_fs_quota_transfer(c, src_inode,
 					     dst_dir->ei_qid,
@@ -783,11 +795,13 @@ static int bch2_setattr(struct mnt_idmap *idmap,
 			struct dentry *dentry, struct iattr *iattr)
 {
 	struct bch_inode_info *inode = to_bch_ei(dentry->d_inode);
+	struct bch_fs *c = inode->v.i_sb->s_fs_info;
 	int ret;
 
 	lockdep_assert_held(&inode->v.i_rwsem);
 
-	ret = setattr_prepare(idmap, dentry, iattr);
+	ret   = bch2_subvol_is_ro(c, inode->ei_subvol) ?:
+		setattr_prepare(idmap, dentry, iattr);
 	if (ret)
 		return ret;
 
@@ -1010,12 +1024,26 @@ static int bch2_vfs_readdir(struct file *file, struct dir_context *ctx)
 	return bch2_err_class(ret);
 }
 
+static int bch2_open(struct inode *vinode, struct file *file)
+{
+	if (file->f_flags & (O_WRONLY|O_RDWR)) {
+		struct bch_inode_info *inode = to_bch_ei(vinode);
+		struct bch_fs *c = inode->v.i_sb->s_fs_info;
+
+		int ret = bch2_subvol_is_ro(c, inode->ei_subvol);
+		if (ret)
+			return ret;
+	}
+
+	return generic_file_open(vinode, file);
+}
+
 static const struct file_operations bch_file_operations = {
+	.open		= bch2_open,
 	.llseek		= bch2_llseek,
 	.read_iter	= bch2_read_iter,
 	.write_iter	= bch2_write_iter,
 	.mmap		= bch2_mmap,
-	.open		= generic_file_open,
 	.fsync		= bch2_fsync,
 	.splice_read	= filemap_splice_read,
 	.splice_write	= iter_file_splice_write,

fs/bcachefs/subvolume.c

@@ -146,6 +146,24 @@ int bch2_subvolume_get(struct btree_trans *trans, unsigned subvol,
 	return bch2_subvolume_get_inlined(trans, subvol, inconsistent_if_not_found, iter_flags, s);
 }
 
+int bch2_subvol_is_ro_trans(struct btree_trans *trans, u32 subvol)
+{
+	struct bch_subvolume s;
+	int ret = bch2_subvolume_get_inlined(trans, subvol, true, 0, &s);
+	if (ret)
+		return ret;
+
+	if (BCH_SUBVOLUME_RO(&s))
+		return -EROFS;
+	return 0;
+}
+
+int bch2_subvol_is_ro(struct bch_fs *c, u32 subvol)
+{
+	return bch2_trans_do(c, NULL, NULL, 0,
+		bch2_subvol_is_ro_trans(trans, subvol));
+}
+
 int bch2_snapshot_get_subvol(struct btree_trans *trans, u32 snapshot,
 			     struct bch_subvolume *subvol)
 {

fs/bcachefs/subvolume.h

@@ -23,6 +23,9 @@ int bch2_subvolume_get(struct btree_trans *, unsigned,
 		       bool, int, struct bch_subvolume *);
 int bch2_subvolume_get_snapshot(struct btree_trans *, u32, u32 *);
 
+int bch2_subvol_is_ro_trans(struct btree_trans *, u32);
+int bch2_subvol_is_ro(struct bch_fs *, u32);
+
 int bch2_delete_dead_snapshots(struct bch_fs *);
 void bch2_delete_dead_snapshots_async(struct bch_fs *);
 

fs/bcachefs/xattr.c

@@ -176,7 +176,8 @@ int bch2_xattr_set(struct btree_trans *trans, subvol_inum inum,
 	struct btree_iter inode_iter = { NULL };
 	int ret;
 
-	ret = bch2_inode_peek(trans, &inode_iter, inode_u, inum, BTREE_ITER_INTENT);
+	ret   = bch2_subvol_is_ro_trans(trans, inum.subvol) ?:
+		bch2_inode_peek(trans, &inode_iter, inode_u, inum, BTREE_ITER_INTENT);
 	if (ret)
 		return ret;