Re: [PATCH 1/4] fs/iso9660: Add check to prevent infinite loop

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

On Wed, 14 Dec 2022 18:55:02 +0000 Lidong Chen <lidong.chen@oracle.com> wrote:
> There is no check for the end of block When reading

s/When/when/

> directory extents. It resulted in read_node() always
> read from the same offset in the while loop, thus
> caused infinite loop. The fix added a check for the
> end of the block and ensure the read is within directory
> boundary.
>
> Signed-off-by: Lidong Chen <lidong.chen@oracle.com>
> ---
>  grub-core/fs/iso9660.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/grub-core/fs/iso9660.c b/grub-core/fs/iso9660.c
> index 91817ec1f..4f4cd6165 100644
> --- a/grub-core/fs/iso9660.c
> +++ b/grub-core/fs/iso9660.c
> @@ -795,6 +795,15 @@ grub_iso9660_iterate_dir (grub_fshelp_node_t dir,
>  	while (dirent.flags & FLAG_MORE_EXTENTS)
>  	  {
>  	    offset += dirent.len;
> +
> +	    /* offset should within the dir's len. */
> +	    if (offset > len)
> +	      {
> +		if (ctx.filename_alloc)
> +		  grub_free (ctx.filename);
> +		return 0;
> +	      }
> +
>  	    if (read_node (dir, offset, sizeof (dirent), (char *) &dirent))
>  	      {
>  		if (ctx.filename_alloc)
> @@ -802,6 +811,18 @@ grub_iso9660_iterate_dir (grub_fshelp_node_t dir,
>  		grub_free (node);
>  		return 0;
>  	      }
> +
> +	    /*
> +	     * It is either the end of block or zero-padded sector,
> +	     * skip to the next block.
> +	     */
> +	    if (!dirent.len)
> +	      {
> +		offset = (offset / GRUB_ISO9660_BLKSZ + 1) * GRUB_ISO9660_BLKSZ;
> +		dirent.flags |= FLAG_MORE_EXTENTS;
> +		continue;
> +	      }
> +
>  	    if (node->have_dirents >= node->alloc_dirents)
>  	      {
>  		struct grub_fshelp_node *new_node;
> --
> 2.35.1
>

Reviewed-by: Thomas Schmitt <scdbackup@gmx.net>

The second hunk will become very necessary when more initrds >= 4 GiB will
be around. Then GRUB might more probably encounter directory records of a
large file which are not stored in the same block.

(Are we aware of the file size limit of 32 GiB - 14 KiB - 1 imposed by
   struct grub_fshelp_node { ... struct grub_iso9660_dir dirents[8]; ... }
 ? )


Have a nice day :)

Thomas