Re: why is i_ino unsigned long, anyway?

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Oct 02, 2013 at 09:05:27AM -0700, Christoph Hellwig wrote:
> On Wed, Oct 02, 2013 at 10:25:27AM -0400, J. Bruce Fields wrote:
> > If so then it's no huge code duplication to it by hand:
> > 
> > 	if (inode->i_op->getattr)
> > 		inode->i_op->getattr(path->mnt, path->dentry, &stat);
> > 	else
> > 		generic_fillattr(inode, &stat);
> 
> Maybe make that a vfs_getattr_nosec and let vfs_getattr call it?
> 
> Including a proper kerneldoc comment explaining when to use it, please.

Something like this?

--b.

commit 8418a41b7192cf2f372ae091207adb29a088f9a0
Author: J. Bruce Fields <bfields@redhat.com>
Date:   Tue Sep 10 11:41:12 2013 -0400

    exportfs: fix 32-bit nfsd handling of 64-bit inode numbers
    
    Symptoms were spurious -ENOENTs on stat of an NFS filesystem from a
    32-bit NFS server exporting a very large XFS filesystem, when the
    server's cache is cold (so the inodes in question are not in cache).
    
    Reported-by: Trevor Cordes <trevor@tecnopolis.ca>
    Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
index 293bc2e..811831a 100644
--- a/fs/exportfs/expfs.c
+++ b/fs/exportfs/expfs.c
@@ -215,7 +215,7 @@ struct getdents_callback {
 	struct dir_context ctx;
 	char *name;		/* name that was found. It already points to a
 				   buffer NAME_MAX+1 is size */
-	unsigned long ino;	/* the inum we are looking for */
+	u64 ino;		/* the inum we are looking for */
 	int found;		/* inode matched? */
 	int sequence;		/* sequence counter */
 };
@@ -255,10 +255,10 @@ static int get_name(const struct path *path, char *name, struct dentry *child)
 	struct inode *dir = path->dentry->d_inode;
 	int error;
 	struct file *file;
+	struct kstat stat;
 	struct getdents_callback buffer = {
 		.ctx.actor = filldir_one,
 		.name = name,
-		.ino = child->d_inode->i_ino
 	};
 
 	error = -ENOTDIR;
@@ -268,6 +268,16 @@ static int get_name(const struct path *path, char *name, struct dentry *child)
 	if (!dir->i_fop)
 		goto out;
 	/*
+	 * inode->i_ino is unsigned long, kstat->ino is u64, so the
+	 * former would be insufficient on 32-bit hosts when the
+	 * filesystem supports 64-bit inode numbers.  So we need to
+	 * actually call ->getattr, not just read i_ino:
+	 */
+	error = vfs_getattr_nosec(path, &stat);
+	if (error)
+		return error;
+	buffer.ino = stat.ino;
+	/*
 	 * Open the directory ...
 	 */
 	file = dentry_open(path, O_RDONLY, cred);
diff --git a/fs/stat.c b/fs/stat.c
index 04ce1ac..71a39e8 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -37,14 +37,21 @@ void generic_fillattr(struct inode *inode, struct kstat *stat)
 
 EXPORT_SYMBOL(generic_fillattr);
 
-int vfs_getattr(struct path *path, struct kstat *stat)
+/**
+ * vfs_getattr_nosec - getattr without security checks
+ * @path: file to get attributes from
+ * @stat: structure to return attributes in
+ *
+ * Get attributes without calling security_inode_getattr.
+ *
+ * Currently the only caller other than vfs_getattr is internal to the
+ * filehandle lookup code, which uses only the inode number and returns
+ * no attributes to any user.  Any other code probably wants
+ * vfs_getattr.
+ */
+int vfs_getattr_nosec(struct path *path, struct kstat *stat)
 {
 	struct inode *inode = path->dentry->d_inode;
-	int retval;
-
-	retval = security_inode_getattr(path->mnt, path->dentry);
-	if (retval)
-		return retval;
 
 	if (inode->i_op->getattr)
 		return inode->i_op->getattr(path->mnt, path->dentry, stat);
@@ -53,6 +60,18 @@ int vfs_getattr(struct path *path, struct kstat *stat)
 	return 0;
 }
 
+EXPORT_SYMBOL_GPL(vfs_getattr_nosec);
+
+int vfs_getattr(struct path *path, struct kstat *stat)
+{
+	int retval;
+
+	retval = security_inode_getattr(path->mnt, path->dentry);
+	if (retval)
+		return retval;
+	return vfs_getattr_nosec(path, stat);
+}
+
 EXPORT_SYMBOL(vfs_getattr);
 
 int vfs_fstat(unsigned int fd, struct kstat *stat)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9818747..5a51faa 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2500,6 +2500,7 @@ extern int page_symlink(struct inode *inode, const char *symname, int len);
 extern const struct inode_operations page_symlink_inode_operations;
 extern int generic_readlink(struct dentry *, char __user *, int);
 extern void generic_fillattr(struct inode *, struct kstat *);
+int vfs_getattr_nosec(struct path *path, struct kstat *stat);
 extern int vfs_getattr(struct path *, struct kstat *);
 void __inode_add_bytes(struct inode *inode, loff_t bytes);
 void inode_add_bytes(struct inode *inode, loff_t bytes);