Revert "ANDROID: overlayfs: override_creds=off option bypass creator_cred"

This reverts commit ae23eedb3f as it
conflicts badly with the overlayfs changes in 6.5-rc1.

If it is still needed, it must come back after the merge is completed,
but really, the option should be submitted upstream as it's been in the
Android tree for a very long time.

Bug: 231996550
Cc: David Anderson <dvander@google.com>
Change-Id: Ide8bd5ac64b1a8955fa14101adc3c48081ce974c
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

Documentation/filesystems/overlayfs.rst

@@ -195,7 +195,7 @@ handle it in two different ways:
 
 1. return EXDEV error: this error is returned by rename(2) when trying to
    move a file or directory across filesystem boundaries.  Hence
-   applications are usually prepared to handle this error (mv(1) for example
+   applications are usually prepared to hande this error (mv(1) for example
    recursively copies the directory tree).  This is the default behavior.
 
 2. If the "redirect_dir" feature is enabled, then the directory will be
@@ -324,30 +324,6 @@ and
 The resulting access permissions should be the same.  The difference is in
 the time of copy (on-demand vs. up-front).
 
-### Non overlapping credentials
-
-As noted above, all access to the upper, lower and work directories is the
-recorded mounter's MAC and DAC credentials.  The incoming accesses are
-checked against the caller's credentials.
-
-In the case where caller MAC or DAC credentials do not overlap the mounter, a
-use case available in older versions of the driver, the override_creds mount
-flag can be turned off.  For when the use pattern has caller with legitimate
-credentials where the mounter does not.  For example init may have been the
-mounter, but the caller would have execute or read MAC permissions where
-init would not.  override_creds off means all access, incoming, upper, lower
-or working, will be tested against the caller.
-
-Several unintended side effects will occur though.  The caller without certain
-key capabilities or lower privilege will not always be able to delete files or
-directories, create nodes, or search some restricted directories.  The ability
-to search and read a directory entry is spotty as a result of the cache
-mechanism not re-testing the credentials because of the assumption, a
-privileged caller can fill cache, then a lower privilege can read the directory
-cache.  The uneven security model where cache, upperdir and workdir are opened
-at privilege, but accessed without creating a form of privilege escalation,
-should only be used with strict understanding of the side effects and of the
-security policies.
 
 Multiple lower layers
 ---------------------

fs/overlayfs/copy_up.c

@@ -1096,7 +1096,7 @@ static int ovl_copy_up_flags(struct dentry *dentry, int flags)
 		dput(parent);
 		dput(next);
 	}
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 
 	return err;
 }

fs/overlayfs/dir.c

@@ -556,7 +556,7 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
 			      struct ovl_cattr *attr, bool origin)
 {
 	int err;
-	const struct cred *old_cred, *hold_cred = NULL;
+	const struct cred *old_cred;
 	struct cred *override_cred;
 	struct dentry *parent = dentry->d_parent;
 
@@ -597,14 +597,13 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
 		override_cred->fsuid = inode->i_uid;
 		override_cred->fsgid = inode->i_gid;
 		err = security_dentry_create_files_as(dentry,
-				attr->mode, &dentry->d_name,
-				old_cred ? old_cred : current_cred(),
+				attr->mode, &dentry->d_name, old_cred,
 				override_cred);
 		if (err) {
 			put_cred(override_cred);
 			goto out_revert_creds;
 		}
-		hold_cred = override_creds(override_cred);
+		put_cred(override_creds(override_cred));
 		put_cred(override_cred);
 	}
 
@@ -614,9 +613,7 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
 		err = ovl_create_over_whiteout(dentry, inode, attr);
 
 out_revert_creds:
-	ovl_revert_creds(dentry->d_sb, old_cred ?: hold_cred);
-	if (old_cred && hold_cred)
-		put_cred(hold_cred);
+	revert_creds(old_cred);
 	return err;
 }
 
@@ -693,7 +690,7 @@ static int ovl_set_link_redirect(struct dentry *dentry)
 
 	old_cred = ovl_override_creds(dentry->d_sb);
 	err = ovl_set_redirect(dentry, false);
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 
 	return err;
 }
@@ -912,7 +909,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir)
 		err = ovl_remove_upper(dentry, is_dir, &list);
 	else
 		err = ovl_remove_and_whiteout(dentry, &list);
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 	if (!err) {
 		if (is_dir)
 			clear_nlink(dentry->d_inode);
@@ -1287,7 +1284,7 @@ out_dput_old:
 out_unlock:
 	unlock_rename(new_upperdir, old_upperdir);
 out_revert_creds:
-	ovl_revert_creds(old->d_sb, old_cred);
+	revert_creds(old_cred);
 	if (update_nlink)
 		ovl_nlink_end(new);
 out_drop_write:

fs/overlayfs/file.c

@@ -60,13 +60,13 @@ static struct file *ovl_open_realfile(const struct file *file,
 	if (err) {
 		realfile = ERR_PTR(err);
 	} else {
-		if (old_cred && !inode_owner_or_capable(real_idmap, realinode))
+		if (!inode_owner_or_capable(real_idmap, realinode))
 			flags &= ~O_NOATIME;
 
 		realfile = backing_file_open(&file->f_path, flags, realpath,
 					     current_cred());
 	}
-	ovl_revert_creds(inode->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",
 		 file, file, ovl_whatisit(inode, realinode), file->f_flags,
@@ -211,7 +211,7 @@ static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
 
 	old_cred = ovl_override_creds(inode->i_sb);
 	ret = vfs_llseek(real.file, offset, whence);
-	ovl_revert_creds(inode->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	file->f_pos = real.file->f_pos;
 	ovl_inode_unlock(inode);
@@ -324,7 +324,7 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 			ovl_aio_cleanup_handler(aio_req);
 	}
 out:
-	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
+	revert_creds(old_cred);
 	ovl_file_accessed(file);
 out_fdput:
 	fdput(real);
@@ -396,7 +396,7 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 			ovl_aio_cleanup_handler(aio_req);
 	}
 out:
-	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
+	revert_creds(old_cred);
 out_fdput:
 	fdput(real);
 
@@ -462,7 +462,7 @@ static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out,
 	file_end_write(real.file);
 	/* Update size */
 	ovl_copyattr(inode);
-	ovl_revert_creds(inode->i_sb, old_cred);
+	revert_creds(old_cred);
 	fdput(real);
 
 out_unlock:
@@ -489,7 +489,7 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 	if (file_inode(real.file) == ovl_inode_upper(file_inode(file))) {
 		old_cred = ovl_override_creds(file_inode(file)->i_sb);
 		ret = vfs_fsync_range(real.file, start, end, datasync);
-		ovl_revert_creds(file_inode(file)->i_sb, old_cred);
+		revert_creds(old_cred);
 	}
 
 	fdput(real);
@@ -513,7 +513,7 @@ static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 
 	old_cred = ovl_override_creds(file_inode(file)->i_sb);
 	ret = call_mmap(vma->vm_file, vma);
-	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
+	revert_creds(old_cred);
 	ovl_file_accessed(file);
 
 	return ret;
@@ -539,7 +539,7 @@ static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len
 
 	old_cred = ovl_override_creds(file_inode(file)->i_sb);
 	ret = vfs_fallocate(real.file, mode, offset, len);
-	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	/* Update size */
 	ovl_copyattr(inode);
@@ -564,7 +564,7 @@ static int ovl_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 
 	old_cred = ovl_override_creds(file_inode(file)->i_sb);
 	ret = vfs_fadvise(real.file, offset, len, advice);
-	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	fdput(real);
 
@@ -623,7 +623,7 @@ static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in,
 						flags);
 		break;
 	}
-	ovl_revert_creds(file_inode(file_out)->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	/* Update size */
 	ovl_copyattr(inode_out);
@@ -685,7 +685,7 @@ static int ovl_flush(struct file *file, fl_owner_t id)
 	if (real.file->f_op->flush) {
 		old_cred = ovl_override_creds(file_inode(file)->i_sb);
 		err = real.file->f_op->flush(real.file, id);
-		ovl_revert_creds(file_inode(file)->i_sb, old_cred);
+		revert_creds(old_cred);
 	}
 	fdput(real);
 

fs/overlayfs/inode.c

@@ -81,7 +81,7 @@ int ovl_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 		inode_lock(upperdentry->d_inode);
 		old_cred = ovl_override_creds(dentry->d_sb);
 		err = ovl_do_notify_change(ofs, upperdentry, attr);
-		ovl_revert_creds(dentry->d_sb, old_cred);
+		revert_creds(old_cred);
 		if (!err)
 			ovl_copyattr(dentry->d_inode);
 		inode_unlock(upperdentry->d_inode);
@@ -273,7 +273,7 @@ int ovl_getattr(struct mnt_idmap *idmap, const struct path *path,
 		stat->nlink = dentry->d_inode->i_nlink;
 
 out:
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 
 	return err;
 }
@@ -311,7 +311,7 @@ int ovl_permission(struct mnt_idmap *idmap,
 		mask |= MAY_READ;
 	}
 	err = inode_permission(mnt_idmap(realpath.mnt), realinode, mask);
-	ovl_revert_creds(inode->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	return err;
 }
@@ -328,7 +328,7 @@ static const char *ovl_get_link(struct dentry *dentry,
 
 	old_cred = ovl_override_creds(dentry->d_sb);
 	p = vfs_get_link(ovl_dentry_real(dentry), done);
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 	return p;
 }
 
@@ -362,7 +362,7 @@ int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
 		ovl_path_lower(dentry, &realpath);
 		old_cred = ovl_override_creds(dentry->d_sb);
 		err = vfs_getxattr(mnt_idmap(realpath.mnt), realdentry, name, NULL, 0);
-		ovl_revert_creds(dentry->d_sb, old_cred);
+		revert_creds(old_cred);
 		if (err < 0)
 			goto out_drop_write;
 	}
@@ -383,7 +383,7 @@ int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
 		WARN_ON(flags != XATTR_REPLACE);
 		err = ovl_do_removexattr(ofs, realdentry, name);
 	}
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 
 	/* copy c/mtime */
 	ovl_copyattr(inode);
@@ -404,7 +404,7 @@ int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
 	ovl_i_path_real(inode, &realpath);
 	old_cred = ovl_override_creds(dentry->d_sb);
 	res = vfs_getxattr(mnt_idmap(realpath.mnt), realpath.dentry, name, value, size);
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 	return res;
 }
 
@@ -432,7 +432,7 @@ ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 
 	old_cred = ovl_override_creds(dentry->d_sb);
 	res = vfs_listxattr(realdentry, list, size);
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 	if (res <= 0 || size == 0)
 		return res;
 
@@ -587,7 +587,7 @@ struct posix_acl *do_ovl_get_acl(struct mnt_idmap *idmap,
 
 		old_cred = ovl_override_creds(inode->i_sb);
 		acl = ovl_get_acl_path(&realpath, posix_acl_xattr_name(type), noperm);
-		ovl_revert_creds(inode->i_sb, old_cred);
+		revert_creds(old_cred);
 	}
 
 	return acl;
@@ -715,7 +715,7 @@ static int ovl_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 
 	old_cred = ovl_override_creds(inode->i_sb);
 	err = realinode->i_op->fiemap(realinode, fieinfo, start, len);
-	ovl_revert_creds(inode->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	return err;
 }
@@ -786,7 +786,7 @@ int ovl_fileattr_set(struct mnt_idmap *idmap,
 		err = ovl_set_protattr(inode, upperpath.dentry, fa);
 		if (!err)
 			err = ovl_real_fileattr_set(&upperpath, fa);
-		ovl_revert_creds(inode->i_sb, old_cred);
+		revert_creds(old_cred);
 
 		/*
 		 * Merge real inode flags with inode flags read from
@@ -848,7 +848,7 @@ int ovl_fileattr_get(struct dentry *dentry, struct fileattr *fa)
 	old_cred = ovl_override_creds(inode->i_sb);
 	err = ovl_real_fileattr_get(&realpath, fa);
 	ovl_fileattr_prot_flags(inode, fa);
-	ovl_revert_creds(inode->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	return err;
 }

fs/overlayfs/namei.c

@@ -1125,7 +1125,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	ovl_dentry_update_reval(dentry, upperdentry,
 			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
 
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 	if (origin_path) {
 		dput(origin_path->dentry);
 		kfree(origin_path);
@@ -1152,7 +1152,7 @@ out_put_upper:
 	kfree(upperredirect);
 out:
 	kfree(d.redirect);
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 	return ERR_PTR(err);
 }
 
@@ -1204,7 +1204,7 @@ bool ovl_lower_positive(struct dentry *dentry)
 			dput(this);
 		}
 	}
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 
 	return positive;
 }

fs/overlayfs/overlayfs.h

@@ -370,7 +370,6 @@ int ovl_want_write(struct dentry *dentry);
 void ovl_drop_write(struct dentry *dentry);
 struct dentry *ovl_workdir(struct dentry *dentry);
 const struct cred *ovl_override_creds(struct super_block *sb);
-void ovl_revert_creds(struct super_block *sb, const struct cred *oldcred);
 int ovl_can_decode_fh(struct super_block *sb);
 struct dentry *ovl_indexdir(struct super_block *sb);
 bool ovl_index_all(struct super_block *sb);

fs/overlayfs/ovl_entry.h

@@ -20,7 +20,6 @@ struct ovl_config {
 	bool metacopy;
 	bool userxattr;
 	bool ovl_volatile;
-	bool override_creds;
 };
 
 struct ovl_sb {

fs/overlayfs/readdir.c

@@ -286,7 +286,7 @@ static int ovl_check_whiteouts(const struct path *path, struct ovl_readdir_data
 		}
 		inode_unlock(dir->d_inode);
 	}
-	ovl_revert_creds(rdd->dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 
 	return err;
 }
@@ -791,7 +791,7 @@ static int ovl_iterate(struct file *file, struct dir_context *ctx)
 	}
 	err = 0;
 out:
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 	return err;
 }
 
@@ -843,7 +843,7 @@ static struct file *ovl_dir_open_realfile(const struct file *file,
 
 	old_cred = ovl_override_creds(file_inode(file)->i_sb);
 	res = ovl_path_open(realpath, O_RDONLY | (file->f_flags & O_LARGEFILE));
-	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	return res;
 }
@@ -969,7 +969,7 @@ int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list)
 
 	old_cred = ovl_override_creds(dentry->d_sb);
 	err = ovl_dir_read_merged(dentry, list, &root);
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 	if (err)
 		return err;
 

fs/overlayfs/super.c

@@ -54,11 +54,6 @@ module_param_named(xino_auto, ovl_xino_auto_def, bool, 0644);
 MODULE_PARM_DESC(xino_auto,
 		 "Auto enable xino feature");
 
-static bool __read_mostly ovl_override_creds_def = true;
-module_param_named(override_creds, ovl_override_creds_def, bool, 0644);
-MODULE_PARM_DESC(ovl_override_creds_def,
-		 "Use mounter's credentials for accesses");
-
 static void ovl_entry_stack_free(struct ovl_entry *oe)
 {
 	unsigned int i;
@@ -396,9 +391,6 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 		seq_puts(m, ",volatile");
 	if (ofs->config.userxattr)
 		seq_puts(m, ",userxattr");
-	if (ofs->config.override_creds != ovl_override_creds_def)
-		seq_show_option(m, "override_creds",
-				ofs->config.override_creds ? "on" : "off");
 	return 0;
 }
 
@@ -454,8 +446,6 @@ enum {
 	OPT_METACOPY_ON,
 	OPT_METACOPY_OFF,
 	OPT_VOLATILE,
-	OPT_OVERRIDE_CREDS_ON,
-	OPT_OVERRIDE_CREDS_OFF,
 	OPT_ERR,
 };
 
@@ -478,8 +468,6 @@ static const match_table_t ovl_tokens = {
 	{OPT_METACOPY_ON,		"metacopy=on"},
 	{OPT_METACOPY_OFF,		"metacopy=off"},
 	{OPT_VOLATILE,			"volatile"},
-	{OPT_OVERRIDE_CREDS_ON,		"override_creds=on"},
-	{OPT_OVERRIDE_CREDS_OFF,	"override_creds=off"},
 	{OPT_ERR,			NULL}
 };
 
@@ -539,7 +527,6 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 	config->redirect_mode = kstrdup(ovl_redirect_mode_def(), GFP_KERNEL);
 	if (!config->redirect_mode)
 		return -ENOMEM;
-	config->override_creds = ovl_override_creds_def;
 
 	while ((p = ovl_next_opt(&opt)) != NULL) {
 		int token;
@@ -641,14 +628,6 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 			config->userxattr = true;
 			break;
 
-		case OPT_OVERRIDE_CREDS_ON:
-			config->override_creds = true;
-			break;
-
-		case OPT_OVERRIDE_CREDS_OFF:
-			config->override_creds = false;
-			break;
-
 		default:
 			pr_err("unrecognized mount option \"%s\" or missing value\n",
 					p);
@@ -2084,6 +2063,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	kfree(splitlower);
 
 	sb->s_root = root_dentry;
+
 	return 0;
 
 out_free_oe:

fs/overlayfs/util.c

@@ -38,18 +38,9 @@ const struct cred *ovl_override_creds(struct super_block *sb)
 {
 	struct ovl_fs *ofs = sb->s_fs_info;
 
-	if (!ofs->config.override_creds)
-		return NULL;
 	return override_creds(ofs->creator_cred);
 }
 
-void ovl_revert_creds(struct super_block *sb, const struct cred *old_cred)
-{
-	if (old_cred)
-		revert_creds(old_cred);
-}
-
-
 /*
  * Check if underlying fs supports file handles and try to determine encoding
  * type, in order to deduce maximum inode number used by fs.
@@ -934,7 +925,7 @@ int ovl_nlink_start(struct dentry *dentry)
 	 * value relative to the upper inode nlink in an upper inode xattr.
 	 */
 	err = ovl_set_nlink_upper(dentry);
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 
 out:
 	if (err)
@@ -952,7 +943,7 @@ void ovl_nlink_end(struct dentry *dentry)
 
 		old_cred = ovl_override_creds(dentry->d_sb);
 		ovl_cleanup_index(dentry);
-		ovl_revert_creds(dentry->d_sb, old_cred);
+		revert_creds(old_cred);
 	}
 
 	ovl_inode_unlock(inode);