fs: use low-level mapping helpers

In a few places the vfs needs to interact with bare k{g,u}ids directly
instead of struct inode. These are just a few. In previous patches we
introduced low-level mapping helpers that are able to support
filesystems mounted an idmapping. This patch simply converts the places
to use these new helpers.

Link: https://lore.kernel.org/r/20211123114227.3124056-7-brauner@kernel.org (v1)
Link: https://lore.kernel.org/r/20211130121032.3753852-7-brauner@kernel.org (v2)
Link: https://lore.kernel.org/r/20211203111707.3901969-7-brauner@kernel.org
Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
CC: linux-fsdevel@vger.kernel.org
Reviewed-by: Seth Forshee <sforshee@digitalocean.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/security/commoncap.c b/security/commoncap.c
index 09479f71ee2e..d288a62e2999 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -419,7 +419,7 @@ int cap_inode_getsecurity(struct user_namespace *mnt_userns,
 	kroot = make_kuid(fs_ns, root);
 
 	/* If this is an idmapped mount shift the kuid. */
-	kroot = kuid_into_mnt(mnt_userns, kroot);
+	kroot = mapped_kuid_fs(mnt_userns, &init_user_ns, kroot);
 
 	/* If the root kuid maps to a valid uid in current ns, then return
 	 * this as a nscap. */
@@ -489,6 +489,7 @@ out_free:
  * @size:	size of @ivalue
  * @task_ns:	user namespace of the caller
  * @mnt_userns:	user namespace of the mount the inode was found from
+ * @fs_userns:	user namespace of the filesystem
  *
  * If the inode has been found through an idmapped mount the user namespace of
  * the vfsmount must be passed through @mnt_userns. This function will then
@@ -498,7 +499,8 @@ out_free:
  */
 static kuid_t rootid_from_xattr(const void *value, size_t size,
 				struct user_namespace *task_ns,
-				struct user_namespace *mnt_userns)
+				struct user_namespace *mnt_userns,
+				struct user_namespace *fs_userns)
 {
 	const struct vfs_ns_cap_data *nscap = value;
 	kuid_t rootkid;
@@ -508,7 +510,7 @@ static kuid_t rootid_from_xattr(const void *value, size_t size,
 		rootid = le32_to_cpu(nscap->rootid);
 
 	rootkid = make_kuid(task_ns, rootid);
-	return kuid_from_mnt(mnt_userns, rootkid);
+	return mapped_kuid_user(mnt_userns, fs_userns, rootkid);
 }
 
 static bool validheader(size_t size, const struct vfs_cap_data *cap)
@@ -559,7 +561,8 @@ int cap_convert_nscap(struct user_namespace *mnt_userns, struct dentry *dentry,
 			/* user is privileged, just write the v2 */
 			return size;
 
-	rootid = rootid_from_xattr(*ivalue, size, task_ns, mnt_userns);
+	rootid = rootid_from_xattr(*ivalue, size, task_ns, mnt_userns,
+				   &init_user_ns);
 	if (!uid_valid(rootid))
 		return -EINVAL;
 
@@ -700,7 +703,7 @@ int get_vfs_caps_from_disk(struct user_namespace *mnt_userns,
 	/* Limit the caps to the mounter of the filesystem
 	 * or the more limited uid specified in the xattr.
 	 */
-	rootkuid = kuid_into_mnt(mnt_userns, rootkuid);
+	rootkuid = mapped_kuid_fs(mnt_userns, &init_user_ns, rootkuid);
 	if (!rootid_owns_currentns(rootkuid))
 		return -ENODATA;