Subject: Re: [PATCH v2 3/6] Make sure fsck_commit_buffer() does not run out of the buffer

From: Junio C Hamano <[email-masked]>
Date: Wed, 10 Sep 2014 10:43:42 -0700

Johannes Schindelin <[email-masked]> writes:

> So far, we assumed that the buffer is NUL terminated, but this is not
> a safe assumption, now that we opened the fsck_object() API to pass a
> buffer directly.
>
> So let's make sure that there is at least an empty line in the buffer.
> That way, our checks would fail if the empty line was encountered
> prematurely, and consequently we can get away with the current string
> comparisons even with non-NUL-terminated buffers are passed to
> fsck_object().
>
> Signed-off-by: Johannes Schindelin <[email-masked]>
> ---
>  fsck.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
>
> diff --git a/fsck.c b/fsck.c
> index dd77628..9dd7d12 100644
> --- a/fsck.c
> +++ b/fsck.c
> @@ -237,6 +237,26 @@ static int fsck_tree(struct tree *item, int strict, fsck_error error_func)
>  	return retval;
>  }
>  
> +static int require_end_of_header(const void *data, unsigned long size,
> +	struct object *obj, fsck_error error_func)
> +{
> +	const char *buffer = (const char *)data;
> +	int i;
> +
> +	for (i = 0; i < size; i++) {
> +		switch (buffer[i]) {
> +		case '\0':
> +			return error_func(obj, FSCK_ERROR,
> +				"invalid message: NUL at offset %d", i);

Isn't this "invalid header"?  After all we haven't escaped this loop
and haven't seen the message part of the commit object (and it is
the same if you are going to later reuse this for tag objects).

> +		case '\n':
> +			if (i + 1 < size && buffer[i + 1] == '\n')
> +				return 0;
> +		}
> +	}
> +
> +	return error_func(obj, FSCK_ERROR, "invalid buffer: missing empty line");

I think you meant "missing end of header" here.

Other than these small nits, the patch looks good from a cursory
read.

> +}
> +
>  static int fsck_ident(const char **ident, struct object *obj, fsck_error error_func)
>  {
>  	char *end;
> @@ -284,6 +304,9 @@ static int fsck_commit_buffer(struct commit *commit, const char *buffer,
>  	unsigned parent_count, parent_line_count = 0;
>  	int err;
>  
> +	if (require_end_of_header(buffer, size, &commit->object, error_func))
> +		return -1;
> +
>  	if (!skip_prefix(buffer, "tree ", &buffer))
>  		return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'tree' line");
>  	if (get_sha1_hex(buffer, tree_sha1) || buffer[40] != '\n')