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Subject[PATCH 5.15 13/28] fs: add is_idmapped_mnt() helper
Date
From: Christian Brauner <christian.brauner@ubuntu.com>

commit bb49e9e730c2906a958eee273a7819f401543d6c upstream.

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 (v1)
Link: https://lore.kernel.org/r/20211130121032.3753852-2-brauner@kernel.org (v2)
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>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/cachefiles/bind.c | 2 +-
fs/ecryptfs/main.c | 2 +-
fs/namespace.c | 2 +-
fs/nfsd/export.c | 2 +-
fs/overlayfs/super.c | 2 +-
fs/proc_namespace.c | 2 +-
include/linux/fs.h | 14 ++++++++++++++
7 files changed, 20 insertions(+), 6 deletions(-)

--- a/fs/cachefiles/bind.c
+++ b/fs/cachefiles/bind.c
@@ -117,7 +117,7 @@ static int cachefiles_daemon_add_cache(s
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;
}
--- a/fs/ecryptfs/main.c
+++ b/fs/ecryptfs/main.c
@@ -537,7 +537,7 @@ static struct dentry *ecryptfs_mount(str
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;
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3936,7 +3936,7 @@ static int can_idmap_mount(const struct
* 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. */
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -427,7 +427,7 @@ static int check_export(struct path *pat
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;
}
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -873,7 +873,7 @@ static int ovl_mount_dir_noesc(const cha
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;
}
--- a/fs/proc_namespace.c
+++ b/fs/proc_namespace.c
@@ -80,7 +80,7 @@ static void show_mnt_opts(struct seq_fil
seq_puts(m, fs_infop->str);
}

- if (mnt_user_ns(mnt) != &init_user_ns)
+ if (is_idmapped_mnt(mnt))
seq_puts(m, ",idmapped");
}

--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2726,6 +2726,20 @@ static inline struct user_namespace *fil
{
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);

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