Unverified Commit 56851bc9 authored by Christian Brauner's avatar Christian Brauner Committed by Christian Brauner (Microsoft)
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internal: add may_write_xattr() 



Split out the generic checks whether an inode allows writing xattrs. Since
security.* and system.* xattrs don't have any restrictions and we're going
to split out posix acls into a dedicated api we will use this helper to
check whether we can write posix acls.

Signed-off-by: default avatarChristian Brauner (Microsoft) <brauner@kernel.org>
parent a56df5d5

fs/internal.h

+1 −0
Original line number Diff line number Diff line
@@ -232,5 +232,6 @@ ssize_t do_getxattr(struct user_namespace *mnt_userns, 
int setxattr_copy(const char __user *name, struct xattr_ctx *ctx);

int do_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,

		struct xattr_ctx *ctx);

int may_write_xattr(struct user_namespace *mnt_userns, struct inode *inode);



ssize_t __kernel_write_iter(struct file *file, struct iov_iter *from, loff_t *pos);

fs/xattr.c

+30 −13
Original line number Diff line number Diff line
@@ -80,6 +80,31 @@ xattr_resolve_name(struct inode *inode, const char **name) 
	return ERR_PTR(-EOPNOTSUPP);

}



/**

 * may_write_xattr - check whether inode allows writing xattr

 * @mnt_userns:	User namespace of the mount the inode was found from

 * @inode: the inode on which to set an xattr

 *

 * Check whether the inode allows writing xattrs. Specifically, we can never

 * set or remove an extended attribute on a read-only filesystem  or on an

 * immutable / append-only inode.

 *

 * We also need to ensure that the inode has a mapping in the mount to

 * not risk writing back invalid i_{g,u}id values.

 *

 * Return: On success zero is returned. On error a negative errno is returned.

 */

int may_write_xattr(struct user_namespace *mnt_userns, struct inode *inode)

{

	if (IS_IMMUTABLE(inode))

		return -EPERM;

	if (IS_APPEND(inode))

		return -EPERM;

	if (HAS_UNMAPPED_ID(mnt_userns, inode))

		return -EPERM;

	return 0;

}



/*

 * Check permissions for extended attribute access.  This is a bit complicated

 * because different namespaces have very different rules.
@@ -88,20 +113,12 @@ static int 
xattr_permission(struct user_namespace *mnt_userns, struct inode *inode,

		 const char *name, int mask)

{

	/*

	 * We can never set or remove an extended attribute on a read-only

	 * filesystem  or on an immutable / append-only inode.

	 */

	if (mask & MAY_WRITE) {

		if (IS_IMMUTABLE(inode) || IS_APPEND(inode))

			return -EPERM;

		/*

		 * Updating an xattr will likely cause i_uid and i_gid

		 * to be writen back improperly if their true value is

		 * unknown to the vfs.

		 */

		if (HAS_UNMAPPED_ID(mnt_userns, inode))

			return -EPERM;

		int ret;



		ret = may_write_xattr(mnt_userns, inode);

		if (ret)

			return ret;

	}



	/*