fs: add is_idmapped_mnt() helper

Multiple places open-code the same check to determine whether a given
mount is idmapped. Introduce a simple helper function that can be used
instead. This allows us to get rid of the fragile open-coding. We will
later change the check that is used to determine whether a given mount
is idmapped. Introducing a helper allows us to do this in a single
place instead of doing it for multiple places.

Link: https://lore.kernel.org/r/20211123114227.3124056-2-brauner@kernel.org
Link: https://lore.kernel.org/r/20211130121032.3753852-2-brauner@kernel.org
Link: https://lore.kernel.org/r/20211203111707.3901969-2-brauner@kernel.org
Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
CC: linux-fsdevel@vger.kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Seth Forshee <sforshee@digitalocean.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/fs/cachefiles/bind.c b/fs/cachefiles/bind.c
index d463d89..146291b 100644 (file)
--- a/fs/cachefiles/bind.c
+++ b/fs/cachefiles/bind.c
@@ -117,7 +117,7 @@ static int cachefiles_daemon_add_cache(struct cachefiles_cache *cache)
        root = path.dentry;
 
        ret = -EINVAL;
-       if (mnt_user_ns(path.mnt) != &init_user_ns) {
+       if (is_idmapped_mnt(path.mnt)) {
                pr_warn("File cache on idmapped mounts not supported");
                goto error_unsupported;
        }

diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
index d66bbd2..2dd23a8 100644 (file)
--- a/fs/ecryptfs/main.c
+++ b/fs/ecryptfs/main.c
@@ -537,7 +537,7 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags
                goto out_free;
        }
 
-       if (mnt_user_ns(path.mnt) != &init_user_ns) {
+       if (is_idmapped_mnt(path.mnt)) {
                rc = -EINVAL;
                printk(KERN_ERR "Mounting on idmapped mounts currently disallowed\n");
                goto out_free;

diff --git a/fs/namespace.c b/fs/namespace.c
index 659a8f3..4994b81 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3936,7 +3936,7 @@ static int can_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt)
         * mapping. It makes things simpler and callers can just create
         * another bind-mount they can idmap if they want to.
         */
-       if (mnt_user_ns(m) != &init_user_ns)
+       if (is_idmapped_mnt(m))
                return -EPERM;
 
        /* The underlying filesystem doesn't support idmapped mounts yet. */

diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index 9421dae..668c752 100644 (file)
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -427,7 +427,7 @@ static int check_export(struct path *path, int *flags, unsigned char *uuid)
                return -EINVAL;
        }
 
-       if (mnt_user_ns(path->mnt) != &init_user_ns) {
+       if (is_idmapped_mnt(path->mnt)) {
                dprintk("exp_export: export of idmapped mounts not yet supported.\n");
                return -EINVAL;
        }

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 265181c..7bb0a47 100644 (file)
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -873,7 +873,7 @@ static int ovl_mount_dir_noesc(const char *name, struct path *path)
                pr_err("filesystem on '%s' not supported\n", name);
                goto out_put;
        }
-       if (mnt_user_ns(path->mnt) != &init_user_ns) {
+       if (is_idmapped_mnt(path->mnt)) {
                pr_err("idmapped layers are currently not supported\n");
                goto out_put;
        }

diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c
index 392ef51..49650e5 100644 (file)
--- a/fs/proc_namespace.c
+++ b/fs/proc_namespace.c
@@ -80,7 +80,7 @@ static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt)
                        seq_puts(m, fs_infop->str);
        }
 
-       if (mnt_user_ns(mnt) != &init_user_ns)
+       if (is_idmapped_mnt(mnt))
                seq_puts(m, ",idmapped");
 }
 

diff --git a/include/linux/fs.h b/include/linux/fs.h
index bbf812c..06cbefd 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2724,6 +2724,20 @@ static inline struct user_namespace *file_mnt_user_ns(struct file *file)
 {
        return mnt_user_ns(file->f_path.mnt);
 }
+
+/**
+ * is_idmapped_mnt - check whether a mount is mapped
+ * @mnt: the mount to check
+ *
+ * If @mnt has an idmapping attached to it @mnt is mapped.
+ *
+ * Return: true if mount is mapped, false if not.
+ */
+static inline bool is_idmapped_mnt(const struct vfsmount *mnt)
+{
+       return mnt_user_ns(mnt) != &init_user_ns;
+}
+
 extern long vfs_truncate(const struct path *, loff_t);
 int do_truncate(struct user_namespace *, struct dentry *, loff_t start,
                unsigned int time_attrs, struct file *filp);