fs: make helpers idmap mount aware

Extend some inode methods with an additional user namespace argument. A
filesystem that is aware of idmapped mounts will receive the user
namespace the mount has been marked with. This can be used for
additional permission checking and also to enable filesystems to
translate between uids and gids if they need to. We have implemented all
relevant helpers in earlier patches.

As requested we simply extend the exisiting inode method instead of
introducing new ones. This is a little more code churn but it's mostly
mechanical and doesnt't leave us with additional inode methods.

Link: https://lore.kernel.org/r/20210121131959.646623-25-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/fs/stat.c b/fs/stat.c
index 2c471c2fd766..fbc171d038aa 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -75,6 +75,7 @@ EXPORT_SYMBOL(generic_fillattr);
 int vfs_getattr_nosec(const struct path *path, struct kstat *stat,
 		      u32 request_mask, unsigned int query_flags)
 {
+	struct user_namespace *mnt_userns;
 	struct inode *inode = d_backing_inode(path->dentry);
 
 	memset(stat, 0, sizeof(*stat));
@@ -91,11 +92,12 @@ int vfs_getattr_nosec(const struct path *path, struct kstat *stat,
 	if (IS_DAX(inode))
 		stat->attributes |= STATX_ATTR_DAX;
 
+	mnt_userns = mnt_user_ns(path->mnt);
 	if (inode->i_op->getattr)
-		return inode->i_op->getattr(path, stat, request_mask,
-					    query_flags);
+		return inode->i_op->getattr(mnt_userns, path, stat,
+					    request_mask, query_flags);
 
-	generic_fillattr(mnt_user_ns(path->mnt), inode, stat);
+	generic_fillattr(mnt_userns, inode, stat);
 	return 0;
 }
 EXPORT_SYMBOL(vfs_getattr_nosec);