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From: Jeff King <peff@peff.net>
To: "Martin Ågren" <martin.agren@gmail.com>
Cc: git@vger.kernel.org, "brian m . carlson" <sandals@crustytoothpaste.net>
Subject: Re: [PATCH 3/3] setup: add `clear_repository_format()`
Date: Wed, 19 Dec 2018 10:48:53 -0500	[thread overview]
Message-ID: <20181219154853.GC14802@sigill.intra.peff.net> (raw)
In-Reply-To: <20181218072528.3870492-4-martin.agren@gmail.com>

On Tue, Dec 18, 2018 at 08:25:28AM +0100, Martin Ågren wrote:

> After we set up a `struct repository_format`, it owns various pieces of
> allocated memory. We then either use those members, because we decide we
> want to use the "candidate" repository format, or we discard the
> candidate / scratch space. In the first case, we transfer ownership of
> the memory to a few global variables. In the latter case, we just
> silently drop the struct and end up leaking memory.
> 
> Introduce a function `clear_repository_format()` which frees the memory
> the struct holds on to. Call it in the code paths where we currently
> leak the memory. Also call it in the error path of
> `read_repository_format()` to clean up any partial result.
> 
> For hygiene, we need to at least set the pointers that we free to NULL.
> For future-proofing, let's zero the entire struct instead. It just means
> that in the error path of `read_...()` we need to restore the error
> sentinel in the `version` field.

This seems reasonable, and I very much agree on the zero-ing (even
though it _shouldn't_ matter due to the "undefined" rule). That also
makes it safe to clear() multiple times, which is a nice property.

> +void clear_repository_format(struct repository_format *format)
> +{
> +	string_list_clear(&format->unknown_extensions, 0);
> +	free(format->work_tree);
> +	free(format->partial_clone);
> +	memset(format, 0, sizeof(*format));
>  }

For the callers that actually pick the values out, I think it might be a
little less error-prone if they actually copied the strings and then
called clear_repository_format(). That avoids leaks of values that they
didn't know or care about (and the cost of an extra strdup for
repository setup is not a big deal).

Something like this on top of your patch, I guess (with the idea being
that functions which return an error would clear the format, but a
"successful" one would get returned back up the stack to
setup_git_directory_gently(), which then clears it before returning.

-- >8 --
diff --git a/setup.c b/setup.c
index babe5ea156..a5699f9ee6 100644
--- a/setup.c
+++ b/setup.c
@@ -470,6 +470,7 @@ static int check_repository_format_gently(const char *gitdir, struct repository_
 			warning("%s", err.buf);
 			strbuf_release(&err);
 			*nongit_ok = -1;
+			clear_repository_format(candidate);
 			return -1;
 		}
 		die("%s", err.buf);
@@ -499,7 +500,7 @@ static int check_repository_format_gently(const char *gitdir, struct repository_
 		}
 		if (candidate->work_tree) {
 			free(git_work_tree_cfg);
-			git_work_tree_cfg = candidate->work_tree;
+			git_work_tree_cfg = xstrdup(candidate->work_tree);
 			inside_work_tree = -1;
 		}
 	} else {
@@ -1158,6 +1159,7 @@ const char *setup_git_directory_gently(int *nongit_ok)
 
 	strbuf_release(&dir);
 	strbuf_release(&gitdir);
+	clear_repository_format(&repo_fmt);
 
 	return prefix;
 }

-Peff

  reply	other threads:[~2018-12-19 15:48 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-18  7:25 [PATCH 0/3] " Martin Ågren
2018-12-18  7:25 ` [PATCH 1/3] setup: drop return value from `read_repository_format()` Martin Ågren
2018-12-19 15:27   ` Jeff King
2018-12-19 21:42     ` Martin Ågren
2018-12-20  0:17     ` brian m. carlson
2018-12-20  2:52       ` Jeff King
2018-12-20  3:45         ` brian m. carlson
2018-12-20 14:53           ` Jeff King
2018-12-18  7:25 ` [PATCH 2/3] setup: do not use invalid `repository_format` Martin Ågren
2018-12-19  0:18   ` brian m. carlson
2018-12-19 21:43     ` Martin Ågren
2018-12-19 15:38   ` Jeff King
2018-12-19 21:46     ` Martin Ågren
2018-12-19 23:17       ` Jeff King
2018-12-20  0:21     ` brian m. carlson
2018-12-18  7:25 ` [PATCH 3/3] setup: add `clear_repository_format()` Martin Ågren
2018-12-19 15:48   ` Jeff King [this message]
2018-12-19 21:49     ` Martin Ågren
2019-01-14 18:34 ` [PATCH v2 0/3] " Martin Ågren
2019-01-14 18:34   ` [PATCH v2 1/3] setup: free old value before setting `work_tree` Martin Ågren
2019-01-14 18:34   ` [PATCH v2 2/3] setup: do not use invalid `repository_format` Martin Ågren
2019-01-15 19:31     ` Jeff King
2019-01-17  6:31       ` Martin Ågren
2019-01-22  7:07         ` Jeff King
2019-01-22 13:34           ` Martin Ågren
2019-01-22 21:45             ` [PATCH v3 0/2] setup: fix memory leaks with `struct repository_format` Martin Ågren
2019-01-22 21:45               ` [PATCH v3 1/2] setup: free old value before setting `work_tree` Martin Ågren
2019-01-22 21:45               ` [PATCH v3 2/2] setup: fix memory leaks with `struct repository_format` Martin Ågren
2019-01-23  5:57                 ` Jeff King
2019-01-24  0:14                   ` brian m. carlson
2019-01-25 19:25                     ` Martin Ågren
2019-01-25 19:24                   ` Martin Ågren
2019-01-25 19:51                     ` Jeff King
2019-02-25 19:21                       ` Martin Ågren
2019-02-26 17:46                         ` Jeff King
2019-02-28 20:36                           ` [PATCH v4 0/2] " Martin Ågren
2019-02-28 20:36                             ` [PATCH v4 1/2] setup: free old value before setting `work_tree` Martin Ågren
2019-02-28 20:36                             ` [PATCH v4 2/2] setup: fix memory leaks with `struct repository_format` Martin Ågren
2019-03-06  4:56                             ` [PATCH v4 0/2] " Jeff King
2019-01-14 18:34   ` [PATCH v2 3/3] setup: add `clear_repository_format()` Martin Ågren

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