[Spice-devel] [PATCH spice-common v2] codegen: Check validity of array members

[Victor Toso]

Hi,

I was doing some tests, seems to work well :)

On Wed, Aug 14, 2019 at 06:08:24PM +0100, Frediano Ziglio wrote:
> Check that combination of fields for an array does not
> lead to unsafe code.
> check_valid method came from generate_c_declaration with
> some more check and it's use in demarshaller to validate
> the array if the structure is not generated.
> 
> Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
> ---
>  python_modules/demarshal.py |  2 ++
>  python_modules/ptypes.py    | 31 ++++++++++++++++++++++++++++++-
>  2 files changed, 32 insertions(+), 1 deletion(-)
> 
> Changes since v1:
> - add comments to explain the checks done

Many thanks for the comments,
    Acked-by: Victor Toso <victortoso at redhat.com>
> 
> diff --git a/python_modules/demarshal.py b/python_modules/demarshal.py
> index acd4b6f..3736976 100644
> --- a/python_modules/demarshal.py
> +++ b/python_modules/demarshal.py
> @@ -315,6 +315,8 @@ def write_validate_pointer_item(writer, container, item, scope, parent_scope, st
>  def write_validate_array_item(writer, container, item, scope, parent_scope, start,
>                                want_nw_size, want_mem_size, want_extra_size):
>      array = item.type
> +    if item.member:
> +        array.check_valid(item.member)
>      is_byte_size = False
>      element_type = array.element_type
>      if array.is_bytes_length():
> diff --git a/python_modules/ptypes.py b/python_modules/ptypes.py
> index 311ce3d..ebe001c 100644
> --- a/python_modules/ptypes.py
> +++ b/python_modules/ptypes.py
> @@ -485,7 +485,36 @@ class ArrayType(Type):
>      def c_type(self):
>          return self.element_type.c_type()
>  
> +    def check_valid(self, member):
> +        # These attribute corresponds to specific structure size
> +        if member.has_attr("chunk") or member.has_attr("as_ptr"):
> +            return
> +        # These attribute indicate that the array is stored in the structure
> +        # as a pointer of the array. If there's no way to retrieve the length
> +        # of the array give error, as the user has no way to do bound checks
> +        if member.has_attr("to_ptr") or member.has_attr("ptr_array"):
> +            if not (self.is_identifier_length() or self.is_constant_length()):
> +                raise Exception("Unsecure, no length of array")
> +            return
> +        # This attribute indicate that the array is store at the end
> +        # of the structure, the user will compute the length from the
> +        # entire message size
> +        if member.has_end_attr():
> +            return
> +        # Avoid bug, the array has no length specified and no space
> +        # would be allocated
> +        if self.is_remaining_length():
> +            raise Exception('C output array is not allocated')
> +        # For constant length (like "foo[5]") the field is a sized array
> +        # For identifier automatically a pointer to allocated data is store,
> +        # in this case user can read the size using the other field specified
> +        # by the identifier
> +        if self.is_constant_length() or self.is_identifier_length():
> +            return
> +        raise NotImplementedError('unknown array %s' % str(self))
> +
>      def generate_c_declaration(self, writer, member):
> +        self.check_valid(member)
>          name = member.name
>          if member.has_attr("chunk"):
>              return writer.writeln('SpiceChunks *%s;' % name)
> @@ -497,7 +526,7 @@ class ArrayType(Type):
>              return writer.writeln('%s *%s;' % (self.c_type(), name))
>          if member.has_attr("ptr_array"):
>              return writer.writeln('%s *%s[0];' % (self.c_type(), name))
> -        if member.has_end_attr() or self.is_remaining_length():
> +        if member.has_end_attr():
>              return writer.writeln('%s %s[0];' % (self.c_type(), name))
>          if self.is_constant_length():
>              return writer.writeln('%s %s[%s];' % (self.c_type(), name, self.size))
> -- 
> 2.20.1
> 
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> Spice-devel at lists.freedesktop.org
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