fs/xfs: Fix issues found while fuzzing the XFS filesystem

While performing fuzz testing with XFS filesystem images with ASAN
enabled, several issues were found where the memory accesses are made
beyond the data that is allocated into the struct grub_xfs_data
structure's data field.

The existing structure didn't store the size of the memory allocated into
the buffer in the data field and had no way to check it. To resolve these
issues, the data size is stored to enable checks into the data buffer.

With these checks in place, the fuzzing corpus no longer cause any crashes.

Signed-off-by: Darren Kenny <[email protected]>
Signed-off-by: Robbie Harwood <[email protected]>
Signed-off-by: Marta Lewandowska <[email protected]>
Signed-off-by: Lidong Chen <[email protected]>
Reviewed-by: Daniel Kiper <[email protected]>

grub-core/fs/xfs.c

@@ -239,6 +239,7 @@ struct grub_fshelp_node
 
 struct grub_xfs_data
 {
+  grub_size_t data_size;
   struct grub_xfs_sblock sblock;
   grub_disk_t disk;
   int pos;
@@ -611,8 +612,20 @@ grub_xfs_read_block (grub_fshelp_node_t node, grub_disk_addr_t fileblock)
     }
   else if (node->inode.format == XFS_INODE_FORMAT_EXT)
     {
+      grub_addr_t exts_end = 0;
+      grub_addr_t data_end = 0;
+
       nrec = grub_be_to_cpu32 (node->inode.nextents);
       exts = (struct grub_xfs_extent *) grub_xfs_inode_data(&node->inode);
+
+      if (grub_mul (sizeof (struct grub_xfs_extent), nrec, &exts_end) ||
+	  grub_add ((grub_addr_t) node->data, exts_end, &exts_end) ||
+	  grub_add ((grub_addr_t) node->data, node->data->data_size, &data_end) ||
+	  exts_end > data_end)
+	{
+	  grub_error (GRUB_ERR_BAD_FS, "invalid number of XFS extents");
+	  return 0;
+	}
     }
   else
     {
@@ -803,6 +816,9 @@ grub_xfs_iterate_dir (grub_fshelp_node_t dir,
 	    grub_uint8_t *inopos = grub_xfs_inline_de_inopos(dir->data, de);
 	    grub_uint8_t c;
 
+	    if ((inopos + (smallino ? 4 : 8)) > (grub_uint8_t *) dir + grub_xfs_fshelp_size (dir->data))
+	      return grub_error (GRUB_ERR_BAD_FS, "not a correct XFS inode");
+
 	    /* inopos might be unaligned.  */
 	    if (smallino)
 	      ino = (((grub_uint32_t) inopos[0]) << 24)
@@ -829,6 +845,10 @@ grub_xfs_iterate_dir (grub_fshelp_node_t dir,
 	    de->name[de->len] = c;
 
 	    de = grub_xfs_inline_next_de(dir->data, head, de);
+
+	    if ((grub_uint8_t *) de >= (grub_uint8_t *) dir + grub_xfs_fshelp_size (dir->data))
+	      return grub_error (GRUB_ERR_BAD_FS, "invalid XFS directory entry");
+
 	  }
 	break;
       }
@@ -897,6 +917,9 @@ grub_xfs_iterate_dir (grub_fshelp_node_t dir,
 		  }
 
 		filename = (char *)(direntry + 1);
+		if (filename + direntry->len - 1 > (char *) tail)
+		  return grub_error (GRUB_ERR_BAD_FS, "invalid XFS directory entry");
+
 		/* The byte after the filename is for the filetype, padding, or
 		   tag, which is not used by GRUB.  So it can be overwritten. */
 		filename[direntry->len] = '\0';
@@ -941,6 +964,8 @@ grub_xfs_mount (grub_disk_t disk)
   if (!data)
     return 0;
 
+  data->data_size = sizeof (struct grub_xfs_data);
+
   grub_dprintf("xfs", "Reading sb\n");
   /* Read the superblock.  */
   if (grub_disk_read (disk, 0, 0,
@@ -962,6 +987,7 @@ grub_xfs_mount (grub_disk_t disk)
   if (! data)
     goto fail;
 
+  data->data_size = sz;
   data->diropen.data = data;
   data->diropen.ino = grub_be_to_cpu64(data->sblock.rootino);
   data->diropen.inode_read = 1;