reflog: close leak of reflog expire entry

find_cfg_ent() allocates a struct reflog_expire_entry_option via
FLEX_ALLOC_MEM and inserts it into a linked list in the
reflog_expire_options structure. The entries in this list are never
freed, resulting in a leak in cmd_reflog_expire and the gc reflog expire
maintenance task:

Direct leak of 39 byte(s) in 1 object(s) allocated from:
    #0 0x7ff975ee6883 in calloc (/lib64/libasan.so.8+0xe6883)
    #1 0x0000010edada in xcalloc ../wrapper.c:154
    #2 0x000000df0898 in find_cfg_ent ../reflog.c:28
    #3 0x000000df0898 in reflog_expire_config ../reflog.c:70
    #4 0x00000095c451 in configset_iter ../config.c:2116
    #5 0x0000006d29e7 in git_config ../config.h:724
    #6 0x0000006d29e7 in cmd_reflog_expire ../builtin/reflog.c:205
    #7 0x0000006d504c in cmd_reflog ../builtin/reflog.c:419
    #8 0x0000007e4054 in run_builtin ../git.c:480
    #9 0x0000007e4054 in handle_builtin ../git.c:746
    #10 0x0000007e8a35 in run_argv ../git.c:813
    #11 0x0000007e8a35 in cmd_main ../git.c:953
    #12 0x000000441e8f in main ../common-main.c:9
    #13 0x7ff9754115f4 in __libc_start_call_main (/lib64/libc.so.6+0x35f4)
    #14 0x7ff9754116a7 in __libc_start_main@@GLIBC_2.34 (/lib64/libc.so.6+0x36a7)
    #15 0x000000444184 in _start (/home/jekeller/libexec/git-core/git+0x444184)

Close this leak by adding a reflog_clear_expire_config() function which
iterates the linked list and frees its elements. Call it upon exit of
cmd_reflog_expire() and reflog_expire_condition().

Add a basic test which covers this leak. While at it, cover the
functionality from commit commit 3cb22b8efe (Per-ref reflog expiry
configuration, 2008-06-15). We've had this support for years, but lacked
any tests.

Co-developed-by: Jeff King <peff@peff.net>
Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/gc.c

@@ -324,6 +324,7 @@ static int reflog_expire_condition(struct gc_config *cfg UNUSED)
 				 count_reflog_entries, &data);
 
 	reflog_expiry_cleanup(&data.policy);
+	reflog_clear_expire_config(&data.policy.opts);
 	return data.count >= data.limit;
 }
 

builtin/reflog.c

@@ -283,6 +283,9 @@ static int cmd_reflog_expire(int argc, const char **argv, const char *prefix,
 					     &cb);
 		free(ref);
 	}
+
+	reflog_clear_expire_config(&opts);
+
 	return status;
 }
 

reflog.c

@@ -81,6 +81,20 @@ int reflog_expire_config(const char *var, const char *value,
 	return 0;
 }
 
+void reflog_clear_expire_config(struct reflog_expire_options *opts)
+{
+	struct reflog_expire_entry_option *ent = opts->entries, *tmp;
+
+	while (ent) {
+		tmp = ent;
+		ent = ent->next;
+		free(tmp);
+	}
+
+	opts->entries = NULL;
+	opts->entries_tail = NULL;
+}
+
 void reflog_expire_options_set_refname(struct reflog_expire_options *cb,
 				       const char *ref)
 {

reflog.h

@@ -34,6 +34,8 @@ struct reflog_expire_options {
 int reflog_expire_config(const char *var, const char *value,
 			 const struct config_context *ctx, void *cb);
 
+void reflog_clear_expire_config(struct reflog_expire_options *opts);
+
 /*
  * Adapt the options so that they apply to the given refname. This applies any
  * per-reference reflog expiry configuration that may exist to the options.

t/t1410-reflog.sh

@@ -673,4 +673,32 @@ test_expect_success 'reflog drop --all with reference' '
 	)
 '
 
+test_expect_success 'expire with pattern config' '
+	# Split refs/heads/ into two roots so we can apply config to each. Make
+	# two branches per root to verify that config is applied correctly
+	# multiple times.
+	git branch root1/branch1 &&
+	git branch root1/branch2 &&
+	git branch root2/branch1 &&
+	git branch root2/branch2 &&
+
+	test_config "gc.reflogexpire" "never" &&
+	test_config "gc.refs/heads/root2/*.reflogExpire" "now" &&
+	git reflog expire \
+		root1/branch1 root1/branch2 \
+		root2/branch1 root2/branch2 &&
+
+	cat >expect <<-\EOF &&
+	root1/branch1@{0}
+	root1/branch2@{0}
+	EOF
+	git log -g --branches="root*" --format=%gD >actual.raw &&
+	# The sole reflog entry of each branch points to the same commit, so
+	# the order in which they are shown is nondeterministic. We just care
+	# about the what was expired (and what was not), so sort to get a known
+	# order.
+	sort <actual.raw >actual.sorted &&
+	test_cmp expect actual.sorted
+'
+
 test_done