# [PATCH] diff-lib: plug minor memory leaks in do_diff_cache()

2 messages from 2020-11-14 to 2020-11-17. Participants: René Scharfe, Jeff King.
Thread: https://gitlist.dev/t/54643

## René Scharfe, 2020-11-14 18:37

Subject: [PATCH] diff-lib: plug minor memory leaks in do_diff_cache()
Message-ID: <80fb4a2a-992f-7d3b-9413-5059da3a8f01@web.de>
URL: https://gitlist.dev/e/80fb4a2a-992f-7d3b-9413-5059da3a8f01%40web.de

```
do_diff_cache() builds a struct rev_info to hand to diff_cache() from
scratch by initializing it using repo_init_revisions() and then
replacing its diffopt and prune_data members.

The diffopt member is initialized to a heap-allocated list of options,
though.  Release it using diff_setup_done() before overwriting it.

The initial value of the prune_data member doesn't need to be released,
but the copy created using copy_pathspec() does.  Clear it after use.

Signed-off-by: René Scharfe <l.s.r@web.de>
---
 diff-lib.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/diff-lib.c b/diff-lib.c
index 082e249fc3..b73cc1859a 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -606,10 +606,12 @@ int do_diff_cache(const struct object_id *tree_oid, struct diff_options *opt)

 	repo_init_revisions(opt->repo, &revs, NULL);
 	copy_pathspec(&revs.prune_data, &opt->pathspec);
+	diff_setup_done(&revs.diffopt);
 	revs.diffopt = *opt;

 	if (diff_cache(&revs, tree_oid, NULL, 1))
 		exit(128);
+	clear_pathspec(&revs.prune_data);
 	return 0;
 }

--
2.29.2

```

## Jeff King, 2020-11-17 00:35

Subject: Re: [PATCH] diff-lib: plug minor memory leaks in do_diff_cache()
Message-ID: <20201117003511.GC13516@coredump.intra.peff.net>
URL: https://gitlist.dev/e/20201117003511.GC13516%40coredump.intra.peff.net
In-Reply-To: <80fb4a2a-992f-7d3b-9413-5059da3a8f01@web.de>

```
On Sat, Nov 14, 2020 at 07:37:03PM +0100, René Scharfe wrote:

> do_diff_cache() builds a struct rev_info to hand to diff_cache() from
> scratch by initializing it using repo_init_revisions() and then
> replacing its diffopt and prune_data members.
> 
> The diffopt member is initialized to a heap-allocated list of options,
> though.  Release it using diff_setup_done() before overwriting it.

Makes sense. This whole "rewrite the options as a heap-allocated list"
thing is pretty gross, but is probably the least-bad solution to the
problem. I wondered if there might be other unpaired diff_setup() /
diff_setup_done() calls. Curiously, there are more of the latter:

  $ git grep 'diff_setup(' | wc -l
  22

  $ git grep 'diff_setup_done(' | wc -l
  35

I think because repo_init_revisions() makes an implicit call to
diff_setup().

> The initial value of the prune_data member doesn't need to be released,
> but the copy created using copy_pathspec() does.  Clear it after use.

I suspect there are more elements of rev_info that could be allocated
(e.g., in a traversal without "--objects", I think trees and blobs are
left sitting in the pending array). It's a prime candidate for UNLEAK()
in most cases where we do a single traversal and then exit the program.
But for sub-functions like this, we perhaps should bite the bullet and
just make a rev_info_clear() function that can be used everywhere.

(I'm not opposed to your patch here in the meantime, though).

-Peff

```