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

This reverts commit 6120a4d780 as it did
not make it into 5.11-rc1 and causes massive merge issues.  If needed,
please forward-port and add it back.

Cc: Mark Salyzyn <salyzyn@android.com>
Bug: 133515582
Bug: 136124883
Bug: 129319403
Change-Id: Ib896e744640d570918af498e1f2bd42d66c33471
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

Documentation/filesystems/overlayfs.rst

@@ -137,29 +137,6 @@ Only the lists of names from directories are merged.  Other content
 such as metadata and extended attributes are reported for the upper
 directory only.  These attributes of the lower directory are hidden.
 
-credentials
------------
-
-By default, 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, a
-use case available in older versions of the driver, the
-override_creds mount flag can be turned off and help when the use
-pattern has caller with legitimate credentials where the mounter
-does not.  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
-retesting 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.
-
 whiteouts and opaque directories
 --------------------------------
 

fs/overlayfs/copy_up.c

@@ -962,7 +962,7 @@ 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

@@ -565,7 +565,7 @@ 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;
 
@@ -592,15 +592,14 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
 		override_cred->fsgid = inode->i_gid;
 		if (!attr->hardlink) {
 			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);
 
 		if (!ovl_dentry_is_whiteout(dentry))
@@ -609,9 +608,7 @@ 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;
 }
 
@@ -687,7 +684,7 @@ 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;
 }
@@ -906,7 +903,7 @@ 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);
@@ -1276,7 +1273,7 @@ static int ovl_rename(struct inode *olddir, struct dentry *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

@@ -59,7 +59,7 @@ static struct file *ovl_open_realfile(const struct file *file,
 		realfile = open_with_fake_path(&file->f_path, flags, realinode,
 					       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,
@@ -209,7 +209,7 @@ 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);
@@ -323,8 +323,7 @@ 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);
 
 	fdput(real);
@@ -389,7 +388,7 @@ 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);
 	fdput(real);
 
 out_unlock:
@@ -412,7 +411,7 @@ static ssize_t ovl_splice_read(struct file *in, loff_t *ppos,
 
 	old_cred = ovl_override_creds(file_inode(in)->i_sb);
 	ret = generic_file_splice_read(real.file, ppos, pipe, len, flags);
-	ovl_revert_creds(file_inode(in)->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	ovl_file_accessed(in);
 	fdput(real);
@@ -433,7 +432,7 @@ ovl_splice_write(struct pipe_inode_info *pipe, struct file *out,
 
 	old_cred = ovl_override_creds(file_inode(out)->i_sb);
 	ret = iter_file_splice_write(pipe, real.file, ppos, len, flags);
-	ovl_revert_creds(file_inode(out)->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	ovl_file_accessed(out);
 	fdput(real);
@@ -457,7 +456,7 @@ 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);
@@ -481,7 +480,7 @@ 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);
 
 	if (ret) {
 		/* Drop reference count from new vm_file value */
@@ -509,7 +508,7 @@ 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(ovl_inode_real(inode), inode);
@@ -531,7 +530,7 @@ 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);
 
@@ -553,7 +552,7 @@ static long ovl_real_ioctl(struct file *file, unsigned int cmd,
 	ret = security_file_ioctl(real.file, cmd, arg);
 	if (!ret)
 		ret = vfs_ioctl(real.file, cmd, arg);
-	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	fdput(real);
 
@@ -742,7 +741,7 @@ 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(ovl_inode_real(inode_out), inode_out);

fs/overlayfs/inode.c

@@ -80,7 +80,7 @@ int ovl_setattr(struct dentry *dentry, struct iattr *attr)
 		inode_lock(upperdentry->d_inode);
 		old_cred = ovl_override_creds(dentry->d_sb);
 		err = notify_change(upperdentry, attr, NULL);
-		ovl_revert_creds(dentry->d_sb, old_cred);
+		revert_creds(old_cred);
 		if (!err)
 			ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
 		inode_unlock(upperdentry->d_inode);
@@ -272,7 +272,7 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
 		stat->nlink = dentry->d_inode->i_nlink;
 
 out:
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 
 	return err;
 }
@@ -306,7 +306,7 @@ int ovl_permission(struct inode *inode, int mask)
 		mask |= MAY_READ;
 	}
 	err = inode_permission(realinode, mask);
-	ovl_revert_creds(inode->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	return err;
 }
@@ -323,7 +323,7 @@ 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;
 }
 
@@ -366,7 +366,7 @@ int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
 		WARN_ON(flags != XATTR_REPLACE);
 		err = vfs_removexattr(realdentry, name);
 	}
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 
 	/* copy c/mtime */
 	ovl_copyattr(d_inode(realdentry), inode);
@@ -388,7 +388,7 @@ int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
 	old_cred = ovl_override_creds(dentry->d_sb);
 	res = __vfs_getxattr(realdentry, d_inode(realdentry), name,
 			     value, size, flags);
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 	return res;
 }
 
@@ -416,7 +416,7 @@ 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;
 
@@ -451,7 +451,7 @@ struct posix_acl *ovl_get_acl(struct inode *inode, int type)
 
 	old_cred = ovl_override_creds(inode->i_sb);
 	acl = get_acl(realinode, type);
-	ovl_revert_creds(inode->i_sb, old_cred);
+	revert_creds(old_cred);
 
 	return acl;
 }
@@ -485,7 +485,7 @@ 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;
 }

fs/overlayfs/namei.c

@@ -1098,7 +1098,7 @@ 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);
@@ -1125,7 +1125,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	kfree(upperredirect);
 out:
 	kfree(d.redirect);
-	ovl_revert_creds(dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 	return ERR_PTR(err);
 }
 
@@ -1177,7 +1177,7 @@ 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

@@ -253,7 +253,6 @@ 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

@@ -18,7 +18,6 @@ struct ovl_config {
 	int xino;
 	bool metacopy;
 	bool ovl_volatile;
-	bool override_creds;
 };
 
 struct ovl_sb {

fs/overlayfs/readdir.c

@@ -286,7 +286,7 @@ static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd)
 		}
 		inode_unlock(dir->d_inode);
 	}
-	ovl_revert_creds(rdd->dentry->d_sb, old_cred);
+	revert_creds(old_cred);
 
 	return err;
 }
@@ -796,7 +796,7 @@ 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;
 }
 
@@ -848,7 +848,7 @@ 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;
 }
@@ -986,7 +986,7 @@ 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

@@ -53,11 +53,6 @@ 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;
@@ -371,9 +366,6 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 			   ofs->config.metacopy ? "on" : "off");
 	if (ofs->config.ovl_volatile)
 		seq_puts(m, ",volatile");
-	if (ofs->config.override_creds != ovl_override_creds_def)
-		seq_show_option(m, "override_creds",
-				ofs->config.override_creds ? "on" : "off");
 	return 0;
 }
 
@@ -426,8 +418,6 @@ enum {
 	OPT_METACOPY_ON,
 	OPT_METACOPY_OFF,
 	OPT_VOLATILE,
-	OPT_OVERRIDE_CREDS_ON,
-	OPT_OVERRIDE_CREDS_OFF,
 	OPT_ERR,
 };
 
@@ -447,8 +437,6 @@ 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}
 };
 
@@ -508,7 +496,6 @@ 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;
@@ -598,14 +585,6 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 			config->ovl_volatile = 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);
@@ -2028,6 +2007,7 @@ 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

@@ -37,17 +37,9 @@ 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.
@@ -831,7 +823,7 @@ 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)
@@ -849,7 +841,7 @@ 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);