[PATCH v3 1/9] worktree: stop being overly intimate with run_command() internals

From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Nov 25, 2021, 22:52 UTC
Message-ID: <patch-v3-1.9-1c3f9de33ad-20211125T224833Z-avarab@gmail.com>
In-Reply-To: <cover-v3-0.9-00000000000-20211125T224833Z-avarab@gmail.com>

From: Eric Sunshine <sunshine@sunshineco.com>

add_worktree() reuses a `child_process` for three run_command() invocations, but to do so, it has overly-intimate knowledge of run-command.c internals. In particular, it knows that it must reset child_process::argv to NULL for each subsequent invocation[*] in order for start_command() to latch the newly-populated child_process::args for each invocation, even though this behavior is not a part of the documented API. Beyond having overly-intimate knowledge of run-command.c internals, the reuse of one `child_process` for three run_command() invocations smells like an unnecessary micro-optimization. Therefore, stop sharing one `child_process` and instead use a new one for each run_command() call.

[*] If child_process::argv is not reset to NULL, then subsequent run_command() invocations will instead incorrectly access a dangling pointer to freed memory which had been allocated by child_process::args on the previous run. This is due to the following code in start_command():

    if (!cmd->argv)
        cmd->argv = cmd->args.v;

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 builtin/worktree.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/builtin/worktree.c b/builtin/worktree.c
index d22ece93e1a..9edd3e2829b 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -355,8 +355,8 @@ static int add_worktree(const char *path, const char *refname,
 		goto done;
 
 	if (opts->checkout) {
-		cp.argv = NULL;
-		strvec_clear(&cp.args);
+		struct child_process cp = CHILD_PROCESS_INIT;
+		cp.git_cmd = 1;
 		strvec_pushl(&cp.args, "reset", "--hard", "--no-recurse-submodules", NULL);
 		if (opts->quiet)
 			strvec_push(&cp.args, "--quiet");
@@ -385,12 +385,11 @@ static int add_worktree(const char *path, const char *refname,
 		const char *hook = find_hook("post-checkout");
 		if (hook) {
 			const char *env[] = { "GIT_DIR", "GIT_WORK_TREE", NULL };
-			cp.git_cmd = 0;
+			struct child_process cp = CHILD_PROCESS_INIT;
 			cp.no_stdin = 1;
 			cp.stdout_to_stderr = 1;
 			cp.dir = path;
 			cp.env = env;
-			cp.argv = NULL;
 			cp.trace2_hook_name = "post-checkout";
 			strvec_pushl(&cp.args, absolute_path(hook),
 				     oid_to_hex(null_oid()),

-- 
2.34.1.838.g779e9098efb