fs/mnt_idmapping: introduce an invalid_mnt_idmap

Link: https://lore.kernel.org/linux-fsdevel/20240904-baugrube-erhoben-b3c1c49a2645@brauner/
Suggested-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/mnt_idmapping.c b/fs/mnt_idmapping.c
index 3c60f1eaca615a24588a3a7e1645dbaf71234774..cbca6500848e5ec5732f0e97a625bc29e641dde2 100644 (file)
--- a/fs/mnt_idmapping.c
+++ b/fs/mnt_idmapping.c
@@ -32,6 +32,15 @@ struct mnt_idmap nop_mnt_idmap = {
 };
 EXPORT_SYMBOL_GPL(nop_mnt_idmap);
 
+/*
+ * Carries the invalid idmapping of a full 0-4294967295 {g,u}id range.
+ * This means that all {g,u}ids are mapped to INVALID_VFS{G,U}ID.
+ */
+struct mnt_idmap invalid_mnt_idmap = {
+       .count  = REFCOUNT_INIT(1),
+};
+EXPORT_SYMBOL_GPL(invalid_mnt_idmap);
+
 /**
  * initial_idmapping - check whether this is the initial mapping
  * @ns: idmapping to check
@@ -75,6 +84,8 @@ vfsuid_t make_vfsuid(struct mnt_idmap *idmap,
 
        if (idmap == &nop_mnt_idmap)
                return VFSUIDT_INIT(kuid);
+       if (idmap == &invalid_mnt_idmap)
+               return INVALID_VFSUID;
        if (initial_idmapping(fs_userns))
                uid = __kuid_val(kuid);
        else
@@ -112,6 +123,8 @@ vfsgid_t make_vfsgid(struct mnt_idmap *idmap,
 
        if (idmap == &nop_mnt_idmap)
                return VFSGIDT_INIT(kgid);
+       if (idmap == &invalid_mnt_idmap)
+               return INVALID_VFSGID;
        if (initial_idmapping(fs_userns))
                gid = __kgid_val(kgid);
        else
@@ -140,6 +153,8 @@ kuid_t from_vfsuid(struct mnt_idmap *idmap,
 
        if (idmap == &nop_mnt_idmap)
                return AS_KUIDT(vfsuid);
+       if (idmap == &invalid_mnt_idmap)
+               return INVALID_UID;
        uid = map_id_up(&idmap->uid_map, __vfsuid_val(vfsuid));
        if (uid == (uid_t)-1)
                return INVALID_UID;
@@ -167,6 +182,8 @@ kgid_t from_vfsgid(struct mnt_idmap *idmap,
 
        if (idmap == &nop_mnt_idmap)
                return AS_KGIDT(vfsgid);
+       if (idmap == &invalid_mnt_idmap)
+               return INVALID_GID;
        gid = map_id_up(&idmap->gid_map, __vfsgid_val(vfsgid));
        if (gid == (gid_t)-1)
                return INVALID_GID;
@@ -296,7 +313,7 @@ struct mnt_idmap *alloc_mnt_idmap(struct user_namespace *mnt_userns)
  */
 struct mnt_idmap *mnt_idmap_get(struct mnt_idmap *idmap)
 {
-       if (idmap != &nop_mnt_idmap)
+       if (idmap != &nop_mnt_idmap && idmap != &invalid_mnt_idmap)
                refcount_inc(&idmap->count);
 
        return idmap;
@@ -312,7 +329,8 @@ EXPORT_SYMBOL_GPL(mnt_idmap_get);
  */
 void mnt_idmap_put(struct mnt_idmap *idmap)
 {
-       if (idmap != &nop_mnt_idmap && refcount_dec_and_test(&idmap->count))
+       if (idmap != &nop_mnt_idmap && idmap != &invalid_mnt_idmap &&
+           refcount_dec_and_test(&idmap->count))
                free_mnt_idmap(idmap);
 }
 EXPORT_SYMBOL_GPL(mnt_idmap_put);

diff --git a/include/linux/mnt_idmapping.h b/include/linux/mnt_idmapping.h
index cd4d5c8781f54e0531bf713fd2d2957c97e41f63..b1b219bc3422417e2ec1776413c039dab821fd02 100644 (file)
--- a/include/linux/mnt_idmapping.h
+++ b/include/linux/mnt_idmapping.h
@@ -9,6 +9,7 @@ struct mnt_idmap;
 struct user_namespace;
 
 extern struct mnt_idmap nop_mnt_idmap;
+extern struct mnt_idmap invalid_mnt_idmap;
 extern struct user_namespace init_user_ns;
 
 typedef struct {