erofs: restrict pcluster size limitations

Error out if {en,de}encoded size of a pcluster is unsupported:
  Maximum supported encoded size (of a pcluster):  1 MiB
  Maximum supported decoded size (of a pcluster): 12 MiB

Users can still choose to use supported large configurations (e.g.,
for archival purposes), but there may be performance penalties in
low-memory scenarios compared to smaller pclusters.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240912074156.2925394-1-hsiangkao@linux.alibaba.com

Author: hsiangkao

fs/erofs/erofs_fs.h

@@ -288,9 +288,12 @@ struct erofs_dirent {
 
 #define EROFS_NAME_LEN      255
 
-/* maximum supported size of a physical compression cluster */
+/* maximum supported encoded size of a physical compressed cluster */
 #define Z_EROFS_PCLUSTER_MAX_SIZE	(1024 * 1024)
 
+/* maximum supported decoded size of a physical compressed cluster */
+#define Z_EROFS_PCLUSTER_MAX_DSIZE	(12 * 1024 * 1024)
+
 /* available compression algorithm types (for h_algorithmtype) */
 enum {
 	Z_EROFS_COMPRESSION_LZ4		= 0,

fs/erofs/zmap.c

@@ -687,32 +687,30 @@ int z_erofs_map_blocks_iter(struct inode *inode, struct erofs_map_blocks *map,
 	int err = 0;
 
 	trace_erofs_map_blocks_enter(inode, map, flags);
-
-	/* when trying to read beyond EOF, leave it unmapped */
-	if (map->m_la >= inode->i_size) {
+	if (map->m_la >= inode->i_size) {	/* post-EOF unmapped extent */
 		map->m_llen = map->m_la + 1 - inode->i_size;
 		map->m_la = inode->i_size;
 		map->m_flags = 0;
-		goto out;
-	}
-
-	err = z_erofs_fill_inode_lazy(inode);
-	if (err)
-		goto out;
-
-	if ((vi->z_advise & Z_EROFS_ADVISE_FRAGMENT_PCLUSTER) &&
-	    !vi->z_tailextent_headlcn) {
-		map->m_la = 0;
-		map->m_llen = inode->i_size;
-		map->m_flags = EROFS_MAP_MAPPED | EROFS_MAP_FULL_MAPPED |
-				EROFS_MAP_FRAGMENT;
-		goto out;
+	} else {
+		err = z_erofs_fill_inode_lazy(inode);
+		if (!err) {
+			if ((vi->z_advise & Z_EROFS_ADVISE_FRAGMENT_PCLUSTER) &&
+			    !vi->z_tailextent_headlcn) {
+				map->m_la = 0;
+				map->m_llen = inode->i_size;
+				map->m_flags = EROFS_MAP_MAPPED |
+					EROFS_MAP_FULL_MAPPED | EROFS_MAP_FRAGMENT;
+			} else {
+				err = z_erofs_do_map_blocks(inode, map, flags);
+			}
+		}
+		if (!err && (map->m_flags & EROFS_MAP_ENCODED) &&
+		    unlikely(map->m_plen > Z_EROFS_PCLUSTER_MAX_SIZE ||
+			     map->m_llen > Z_EROFS_PCLUSTER_MAX_DSIZE))
+			err = -EOPNOTSUPP;
+		if (err)
+			map->m_llen = 0;
 	}
-
-	err = z_erofs_do_map_blocks(inode, map, flags);
-out:
-	if (err)
-		map->m_llen = 0;
 	trace_erofs_map_blocks_exit(inode, map, flags, err);
 	return err;
 }