erofs: fix file handle encoding for 64-bit NIDs

EROFS uses NID to indicate the on-disk inode offset, which can
exceed 32 bits. However, the default encode_fh uses the ino32,
thus it doesn't work if the image is larger than 128GiB.

Let's introduce our own helpers to encode file handles.

It's easy to reproduce:
  1. prepare an erofs image with nid bigger than U32_MAX
  2. mount -t erofs foo.img /mnt/erofs
  3. set exportfs with configuration: /mnt/erofs *(rw,sync,
     no_root_squash)
  4. mount -t nfs $IP:/mnt/erofs /mnt/nfs
  5. md5sum /mnt/nfs/foo # foo is the file which nid bigger
     than U32_MAX.  # you will get ESTALE error.

In the case of overlayfs, the underlying filesystem's file
handle is encoded in ovl_fb.fid, which is similar to NFS's
case. If the NID of file is larger than U32_MAX, the overlay
will get -ESTALE error when calls exportfs_decode_fh.

Fixes: 3e917cc ("erofs: make filesystem exportable")
Signed-off-by: Hongbo Li <[email protected]>
Reviewed-by: Gao Xiang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Gao Xiang <[email protected]>

Author: Hongbo Li

fs/erofs/super.c

@@ -510,24 +510,52 @@ static int erofs_fc_parse_param(struct fs_context *fc,
 	return 0;
 }
 
-static struct inode *erofs_nfs_get_inode(struct super_block *sb,
-					 u64 ino, u32 generation)
+static int erofs_encode_fh(struct inode *inode, u32 *fh, int *max_len,
+			   struct inode *parent)
 {
-	return erofs_iget(sb, ino);
+	erofs_nid_t nid = EROFS_I(inode)->nid;
+	int len = parent ? 6 : 3;
+
+	if (*max_len < len) {
+		*max_len = len;
+		return FILEID_INVALID;
+	}
+
+	fh[0] = (u32)(nid >> 32);
+	fh[1] = (u32)(nid & 0xffffffff);
+	fh[2] = inode->i_generation;
+
+	if (parent) {
+		nid = EROFS_I(parent)->nid;
+
+		fh[3] = (u32)(nid >> 32);
+		fh[4] = (u32)(nid & 0xffffffff);
+		fh[5] = parent->i_generation;
+	}
+
+	*max_len = len;
+	return parent ? FILEID_INO64_GEN_PARENT : FILEID_INO64_GEN;
 }
 
 static struct dentry *erofs_fh_to_dentry(struct super_block *sb,
 		struct fid *fid, int fh_len, int fh_type)
 {
-	return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
-				    erofs_nfs_get_inode);
+	if ((fh_type != FILEID_INO64_GEN &&
+	     fh_type != FILEID_INO64_GEN_PARENT) || fh_len < 3)
+		return NULL;
+
+	return d_obtain_alias(erofs_iget(sb,
+		((u64)fid->raw[0] << 32) | fid->raw[1]));
 }
 
 static struct dentry *erofs_fh_to_parent(struct super_block *sb,
 		struct fid *fid, int fh_len, int fh_type)
 {
-	return generic_fh_to_parent(sb, fid, fh_len, fh_type,
-				    erofs_nfs_get_inode);
+	if (fh_type != FILEID_INO64_GEN_PARENT || fh_len < 6)
+		return NULL;
+
+	return d_obtain_alias(erofs_iget(sb,
+		((u64)fid->raw[3] << 32) | fid->raw[4]));
 }
 
 static struct dentry *erofs_get_parent(struct dentry *child)
@@ -543,7 +571,7 @@ static struct dentry *erofs_get_parent(struct dentry *child)
 }
 
 static const struct export_operations erofs_export_ops = {
-	.encode_fh = generic_encode_ino32_fh,
+	.encode_fh = erofs_encode_fh,
 	.fh_to_dentry = erofs_fh_to_dentry,
 	.fh_to_parent = erofs_fh_to_parent,
 	.get_parent = erofs_get_parent,