Re: [PATCH v2 4/5] fs/iso9660: Incorrect check for entry boundary

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

Hi,

On  Wed, 18 Jan 2023 08:23:57 +0000 Lidong Chen <lidong.chen@oracle.com> wrote:
> An SL entry consists of the entry info and the component area.
> The entry info should take up 5 bytes instead of sizeof (*entry).
> The area after the first 5 bytes is the component area. It is
> incorrect to use the sizeof (*entry) to check the entry boundary.
>
> Signed-off-by: Lidong Chen <lidong.chen@oracle.com>
> Reviewed-by: Thomas Schmitt <scdbackup@gmx.net>
> ---
>  grub-core/fs/iso9660.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/grub-core/fs/iso9660.c b/grub-core/fs/iso9660.c
> index c6d65fc22..ca45b3424 100644
> --- a/grub-core/fs/iso9660.c
> +++ b/grub-core/fs/iso9660.c
> @@ -663,10 +663,23 @@ susp_iterate_dir (struct grub_iso9660_susp_entry *entry,
>    else if (grub_strncmp ("SL", (char *) entry->sig, 2) == 0)
>      {
>        unsigned int pos = 1;
> +      unsigned int csize;
>
> -      /* The symlink is not stored as a POSIX symlink, translate it.  */
> -      while (pos + sizeof (*entry) < entry->len)
> +      /* The symlink is not stored as a POSIX symlink, translate it. */
> +      while ((pos + GRUB_ISO9660_SUSP_HEADER_SZ + 1) < entry->len)
>  	{
> +	  /*
> +	   * entry->len is GRUB_ISO9660_SUSP_HEADER_SZ + 1 (the FLAGS)
> +	   * + length of the "Component Area". The length of a component
> +	   * record is 2 (pos and pos + 1) plus the "Component Content",
> +	   * of which starts at pos + 2. entry->data[pos] is the
> +	   * 'Component Flags'; entry->data[pos + 1] is the length
> +	   * of the component.
> +	   */
> +          csize = entry->data[pos + 1] + 2;
> +          if (GRUB_ISO9660_SUSP_HEADER_SZ + 1 + csize > entry->len)
> +            break;
> +
>  	  /* The current position is the `Component Flag'.  */
>  	  switch (entry->data[pos] & 30)
>  	    {
> --
> 2.35.1

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

Most of my initial objections towards patch 4 were wrong. What remained
is taken into respect now.


Have a nice day :)

Thomas