[PATCH 16/18] ovl: handle idmappings in layer open helpers

[Christian Brauner <brauner@kernel.org>]

In earlier patches we already passed down the relevant upper or lower
path to ovl_open_realfile(). Now let the open helpers actually take the
idmapping of the relevant mount into account when checking permissions.
This is needed to support idmapped base layers with overlay.

Cc: <linux-unionfs@vger.kernel.org>
Tested-by: Giuseppe Scrivano <gscrivan@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
---
 fs/overlayfs/file.c | 7 +++++--
 fs/overlayfs/util.c | 5 +++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 656c30bf20a6..7dd44f4e2757 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -42,6 +42,7 @@ static struct file *ovl_open_realfile(const struct file *file,
 {
 	struct inode *realinode = d_inode(realpath->dentry);
 	struct inode *inode = file_inode(file);
+	struct user_namespace *real_idmap;
 	struct file *realfile;
 	const struct cred *old_cred;
 	int flags = file->f_flags | OVL_OPEN_FLAGS;
@@ -51,12 +52,14 @@ static struct file *ovl_open_realfile(const struct file *file,
 	if (flags & O_APPEND)
 		acc_mode |= MAY_APPEND;
 
+
 	old_cred = ovl_override_creds(inode->i_sb);
-	err = inode_permission(&init_user_ns, realinode, MAY_OPEN | acc_mode);
+	real_idmap = mnt_user_ns(realpath->mnt);
+	err = inode_permission(real_idmap, realinode, MAY_OPEN | acc_mode);
 	if (err) {
 		realfile = ERR_PTR(err);
 	} else {
-		if (!inode_owner_or_capable(&init_user_ns, realinode))
+		if (!inode_owner_or_capable(real_idmap, realinode))
 			flags &= ~O_NOATIME;
 
 		realfile = open_with_fake_path(&file->f_path, flags, realinode,
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 79fae06ee10a..7dd2e5e6662a 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -523,6 +523,7 @@ bool ovl_is_whiteout(struct dentry *dentry)
 struct file *ovl_path_open(struct path *path, int flags)
 {
 	struct inode *inode = d_inode(path->dentry);
+	struct user_namespace *real_idmap = mnt_user_ns(path->mnt);
 	int err, acc_mode;
 
 	if (flags & ~(O_ACCMODE | O_LARGEFILE))
@@ -539,12 +540,12 @@ struct file *ovl_path_open(struct path *path, int flags)
 		BUG();
 	}
 
-	err = inode_permission(&init_user_ns, inode, acc_mode | MAY_OPEN);
+	err = inode_permission(real_idmap, inode, acc_mode | MAY_OPEN);
 	if (err)
 		return ERR_PTR(err);
 
 	/* O_NOATIME is an optimization, don't fail if not permitted */
-	if (inode_owner_or_capable(&init_user_ns, inode))
+	if (inode_owner_or_capable(real_idmap, inode))
 		flags |= O_NOATIME;
 
 	return dentry_open(path, flags, current_cred());
-- 
2.32.0