Re: [BUG?] git range-diff -Ix @{1}... segfaults

["René Scharfe" <l.s.r@web.de>]

Am 03.09.21 um 20:49 schrieb Junio C Hamano:
> It does not seem to trigger with an empty range, e.g.
>
>     $ git range-diff -Ix HEAD...
>     $ git range-diff -Ix HEAD~...
>     -:  ---------- > 1:  0a0bc7d03a scalar: accept -C and -c opt...
>
> but when it needs real comparison, the -I seems to kill the command
> quite easily.

Reverting c45dc9cf30 (diff: plug memory leak from regcomp() on
{log,diff} -I, 2021-02-11) fixes the segfault.

diff.c::diff_free() frees the ignore_regex member of a struct
diff_options, but doesn't reset the ignore_regex_nr nor clears the
pointer.  It is called from diff.c::diff_flush().

range-diff.c::output() calls diff.c::diff_flush() in a loop with the
same struct diff_options (via range-diff.c::patch_diff()).

So the second iteration of that loop tries to use the already freed
ignore regexes.  Here's a patch for that:

--- >8 ---
Subject: [PATCH] range-diff: avoid segfault with -I

output() reuses the same struct diff_options for multiple calls of
diff_flush().  Set the option no_free to instruct it to keep the
ignore regexes between calls and release them explicitly at the end.

Signed-off-by: René Scharfe <l.s.r@web.de>
---
Test missing because I couldn't see any effect of -I on range-diff.

 range-diff.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/range-diff.c b/range-diff.c
index e731525e66..cac89a2f4f 100644
--- a/range-diff.c
+++ b/range-diff.c
@@ -482,6 +482,7 @@ static void output(struct string_list *a, struct string_list *b,
 	else
 		diff_setup(&opts);

+	opts.no_free = 1;
 	if (!opts.output_format)
 		opts.output_format = DIFF_FORMAT_PATCH;
 	opts.flags.suppress_diff_headers = 1;
@@ -542,6 +543,8 @@ static void output(struct string_list *a, struct string_list *b,
 	strbuf_release(&buf);
 	strbuf_release(&dashes);
 	strbuf_release(&indent);
+	opts.no_free = 0;
+	diff_free(&opts);
 }

 int show_range_diff(const char *range1, const char *range2,
--
2.33.0