Re: [PATCH 1/2] submodule--helper, module_clone: always operate on absolute paths

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 1, 2016, 19:30 UTC
Message-ID: <xmqq37r5i0tv.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <xmqq7fghi1ds.fsf@gitster.mtv.corp.google.com>

Junio C Hamano <gitster@pobox.com> writes:

Show 18 quoted lines

> By the way, this line is the last use of sm_gitdir_rel before it
> gets freed.  I wonder
>
> 	sm_gitdir = absolute_path(sb.buf);
>
> would be sufficient.  We can lose the variable, and free() on it at
> the end of this function, and an extra allocation if we can do so.
>
>> +	if (!is_absolute_path(path)) {
>> +		strbuf_addf(&sb, "%s/%s", get_git_work_tree(), path);
>> +		path = strbuf_detach(&sb, 0);
>> +	} else
>> +		path = xstrdup(path);
>>  
>>  	if (!file_exists(sm_gitdir)) {
>>  		if (safe_create_leading_directories_const(sm_gitdir) < 0)
>
> Other than that, looks good to me.

Another thing I noticed is that it will not stay safe forever to borrow the result from absolute_path() for extended period of time. So how about this one (and Ramsay's "NULL must be spelled NULL, not 0") on top?

-- >8 --
From: Junio C Hamano <gitster@pobox.com>
Date: Fri, 1 Apr 2016 12:23:16 -0700
Subject: [PATCH] submodule--helper: do not borrow absolute_path() result for too long

absolute_path() is designed to allow its callers to take a brief peek of the result (typically, to be fed to functions like strbuf_add() and relative_path() as a parameter) without having to worry about freeing it, but the other side of the coin of that memory model is that the caller shouldn't rely too much on the result living forever--there may be a helper function the caller subsequently calls that makes its own call to absolute_path(), invalidating the earlier result.

Use xstrdup() to make our own copy, and free(3) it when we are done. While at it, remove an unnecessary sm_gitdir_rel variable that was only used to as a parameter to call absolute_paht() and never used again.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin/submodule--helper.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index b660a22..e69b340 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -157,8 +157,7 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 	const char *reference = NULL, *depth = NULL;
 	int quiet = 0;
 	FILE *submodule_dot_git;
-	char *sm_gitdir_rel, *p, *path = NULL;
-	const char *sm_gitdir;
+	char *p, *path = NULL, *sm_gitdir;
 	struct strbuf rel_path = STRBUF_INIT;
 	struct strbuf sb = STRBUF_INIT;
 
@@ -199,8 +198,7 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 		die(_("submodule--helper: unspecified or empty --path"));
 
 	strbuf_addf(&sb, "%s/modules/%s", get_git_dir(), name);
-	sm_gitdir_rel = strbuf_detach(&sb, NULL);
-	sm_gitdir = absolute_path(sm_gitdir_rel);
+	sm_gitdir = xstrdup(absolute_path(sb.buf));
 
 	if (!is_absolute_path(path)) {
 		strbuf_addf(&sb, "%s/%s", get_git_work_tree(), path);
@@ -245,7 +243,7 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 			       relative_path(path, sm_gitdir, &rel_path));
 	strbuf_release(&sb);
 	strbuf_release(&rel_path);
-	free(sm_gitdir_rel);
+	free(sm_gitdir);
 	free(path);
 	free(p);
 	return 0;

-- 
2.8.0-225-g297c00e