Subject: Re: [PATCH] revision: fix missing null for freed memory

From: Junio C Hamano <[email-masked]>
Date: Mon, 10 Feb 2025 08:02:14 -0800

Emily M Klassen <[email-masked]> writes:

> Subject: Re: [PATCH] revision: fix missing null for freed memory
>
> "git log --graph --no-graph" missed cleaning up the output_prefix and
> output_prefix_data pointers. This resulted in a segfault when using "--patch",
> "--name-status" or "--name-only", as the output_prefix_data continued to be in
> use after free()

Rereading the title, I cannot make sense out of "fix missing null"
and guess what it wants to say.  Is "null" here used as a verb to
mean "to assign a NULL to a variable that points at ..."?

    revision: clear graph callback upon "--no-graph"

    "git log --graph --no-graph" first populates the .output_prefix
    member of diffopt, which is a callback function, to compute
    "--graph" header, and then discards the data the callback needs
    to compute the graph header but forgets to clear .output_prefix
    pointer in response to "--no-graph".  At runtime, we end up
    calling the function that we should not.

    Clear the member to stop making callback, and for a better
    hyginene, also clear the pointer pointing at a freed memory.

or something?

Other than that, as I said earlier, the patch looks good.

Thanks.

> Signed-off-by: Emily M Klassen <[email-masked]>
> ---
> I previously reported this a few hours ago, and ended up digging in and figuring
> it out. I'll make sure to bottom reply in the follow ups to this patch.
>
>  revision.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/revision.c b/revision.c
> index 474fa1e767..84cb028e11 100644
> --- a/revision.c
> +++ b/revision.c
> @@ -2615,6 +2615,8 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
>  		graph_clear(revs->graph);
>  		revs->graph = graph_init(revs);
>  	} else if (!strcmp(arg, "--no-graph")) {
> +		revs->diffopt.output_prefix = NULL;
> +		revs->diffopt.output_prefix_data = NULL;
>  		graph_clear(revs->graph);
>  		revs->graph = NULL;
>  	} else if (!strcmp(arg, "--encode-email-headers")) {