Merge branch 'for-v5.12-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

Pull userns fix from Eric Biederman:
 "Removing the ambiguity broke userspace so this reverts the change"

* 'for-v5.12-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  Revert 95ebabd ("capabilities: Don't allow writing ambiguous v3 file capabilities")

Author: torvalds

security/commoncap.c

@@ -543,8 +543,7 @@ int cap_convert_nscap(struct user_namespace *mnt_userns, struct dentry *dentry,
 	__u32 magic, nsmagic;
 	struct inode *inode = d_backing_inode(dentry);
 	struct user_namespace *task_ns = current_user_ns(),
-		*fs_ns = inode->i_sb->s_user_ns,
-		*ancestor;
+		*fs_ns = inode->i_sb->s_user_ns;
 	kuid_t rootid;
 	size_t newsize;
 
@@ -567,15 +566,6 @@ int cap_convert_nscap(struct user_namespace *mnt_userns, struct dentry *dentry,
 	if (nsrootid == -1)
 		return -EINVAL;
 
-	/*
-	 * Do not allow allow adding a v3 filesystem capability xattr
-	 * if the rootid field is ambiguous.
-	 */
-	for (ancestor = task_ns->parent; ancestor; ancestor = ancestor->parent) {
-		if (from_kuid(ancestor, rootid) == 0)
-			return -EINVAL;
-	}
-
 	newsize = sizeof(struct vfs_ns_cap_data);
 	nscap = kmalloc(newsize, GFP_ATOMIC);
 	if (!nscap)