diff mbox series

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

Message ID patch-v3-1.9-1c3f9de33ad-20211125T224833Z-avarab@gmail.com (mailing list archive)
State Accepted
Commit 33c997a411b14b0ac54452d79c6951cbf109475c
Headers show
Series run-command API: get rid of "argv" and "env" | expand

Commit Message

Ævar Arnfjörð Bjarmason Nov. 25, 2021, 10:52 p.m. UTC 
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(-)

Comments

Eric Sunshine Nov. 26, 2021, 9:48 a.m. UTC | #1 
On Thu, Nov 25, 2021 at 5:52 PM Ævar Arnfjörð Bjarmason
<avarab@gmail.com> wrote:
> 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 people feel uncomfortable with the way this patch shadows `cp` in
nested blocks, an alternative would be to call child_process_init(&cp)
to reuse the existing `cp`, similar to the fix[1] applied to pager.c
when reusing a `child_process`. I don't feel strongly about it either
way.

[1]: https://lore.kernel.org/git/20211125000239.2336-1-ematsumiya@suse.de/

> [*] 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
diff mbox series

Patch

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()),