[PATCH] sequencer: fix memory leak if `todo_list_rearrange_squash()` failed

[PATCH] sequencer: fix memory leak if `todo_list_rearrange_squash()` failed

[Lidong Yan via GitGitGadget]

From: Lidong Yan <502024330056@smail.nju.edu.cn>

In sequencer.c:todo_list_rearrange_squash, if it fails, memory
allocated in `next`, `tail`, `subjects` and `subject2item` will leak.
Jump to cleanup label before return could fix this leak problem.

Signed-off-by: Lidong Yan <502024330056@smail.nju.edu.cn>
---
    sequencer: fix memory leak if todo_list_rearrange_squash() failed
    
    In sequencer.c:todo_list_rearrange_squash, if it fails, memory allocated
    in next, tail, subjects and subject2item will leak. Jump to cleanup
    label before return could fix this leak problem.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1965%2Fbrandb97%2Ffix-sequencer-todo-leak-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1965/brandb97/fix-sequencer-todo-leak-v1
Pull-Request: https://github.com/git/git/pull/1965

 sequencer.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index b5c4043757e..5fb7b68a7ab 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -6596,6 +6596,7 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
 	char **subjects;
 	struct commit_todo_item commit_todo;
 	struct todo_item *items = NULL;
+	int ret = 0;
 
 	init_commit_todo_item(&commit_todo);
 	/*
@@ -6626,8 +6627,8 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
 		}
 
 		if (is_fixup(item->command)) {
-			clear_commit_todo_item(&commit_todo);
-			return error(_("the script was already rearranged."));
+			ret = error(_("the script was already rearranged."));
+			goto cleanup;
 		}
 
 		repo_parse_commit(the_repository, item->commit);
@@ -6729,6 +6730,7 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
 		todo_list->items = items;
 	}
 
+cleanup:
 	free(next);
 	free(tail);
 	for (i = 0; i < todo_list->nr; i++)
@@ -6738,7 +6740,7 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
 
 	clear_commit_todo_item(&commit_todo);
 
-	return 0;
+	return ret;
 }
 
 int sequencer_determine_whence(struct repository *r, enum commit_whence *whence)

base-commit: 6f84262c44a89851c3ae5a6e4c1a9d06b2068d75
-- 
gitgitgadget

Re: [PATCH] sequencer: fix memory leak if `todo_list_rearrange_squash()` failed

[Phillip Wood]

On 14/05/2025 14:53, Lidong Yan via GitGitGadget wrote:
> From: Lidong Yan <502024330056@smail.nju.edu.cn>
> 
> In sequencer.c:todo_list_rearrange_squash, if it fails, memory
> allocated in `next`, `tail`, `subjects` and `subject2item` will leak.
> Jump to cleanup label before return could fix this leak problem.

You could mention that you're adding the cleanup label.

I suspect reaching this condition is a bug as well because we should 
only rearrange the todo list when the rebase starts. However I'm not 
100% sure that it is impossible to trigger this condition so lets free 
it as you suggest. The code changes look good.

Out of interest how are you finding these leaks?

Thanks

Phillip

> Signed-off-by: Lidong Yan <502024330056@smail.nju.edu.cn>
> ---
>      sequencer: fix memory leak if todo_list_rearrange_squash() failed
>      
>      In sequencer.c:todo_list_rearrange_squash, if it fails, memory allocated
>      in next, tail, subjects and subject2item will leak. Jump to cleanup
>      label before return could fix this leak problem.
> 
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1965%2Fbrandb97%2Ffix-sequencer-todo-leak-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1965/brandb97/fix-sequencer-todo-leak-v1
> Pull-Request: https://github.com/git/git/pull/1965
> 
>   sequencer.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/sequencer.c b/sequencer.c
> index b5c4043757e..5fb7b68a7ab 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -6596,6 +6596,7 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
>   	char **subjects;
>   	struct commit_todo_item commit_todo;
>   	struct todo_item *items = NULL;
> +	int ret = 0;
>   
>   	init_commit_todo_item(&commit_todo);
>   	/*
> @@ -6626,8 +6627,8 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
>   		}
>   
>   		if (is_fixup(item->command)) {
> -			clear_commit_todo_item(&commit_todo);
> -			return error(_("the script was already rearranged."));
> +			ret = error(_("the script was already rearranged."));
> +			goto cleanup;
>   		}
>   
>   		repo_parse_commit(the_repository, item->commit);
> @@ -6729,6 +6730,7 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
>   		todo_list->items = items;
>   	}
>   
> +cleanup:
>   	free(next);
>   	free(tail);
>   	for (i = 0; i < todo_list->nr; i++)
> @@ -6738,7 +6740,7 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
>   
>   	clear_commit_todo_item(&commit_todo);
>   
> -	return 0;
> +	return ret;
>   }
>   
>   int sequencer_determine_whence(struct repository *r, enum commit_whence *whence)
> 
> base-commit: 6f84262c44a89851c3ae5a6e4c1a9d06b2068d75

Re: [PATCH] sequencer: fix memory leak if `todo_list_rearrange_squash()` failed

[lidongyan]

2025/5/15 18:08，Phillip Wood <phillip.wood123@gmail.com> 写道：
> 
> On 14/05/2025 14:53, Lidong Yan via GitGitGadget wrote:
>> From: Lidong Yan <502024330056@smail.nju.edu.cn>
>> In sequencer.c:todo_list_rearrange_squash, if it fails, memory
>> allocated in `next`, `tail`, `subjects` and `subject2item` will leak.
>> Jump to cleanup label before return could fix this leak problem.
> 
> You could mention that you're adding the cleanup label.

Understood. I will pay attention to this in future patches.

> Out of interest how are you finding these leaks?

I am a graduate student at Nanjing University, working in 
collaboration with Professor [Qingkai Shi](https://qingkaishi.github.io/). 
We are currently developing a tool for statically analyzing
memory leaks in C programs, and I am testing this tool on Git.
To ensure the validity of our testing results, we are submitting
patches to Git and seeking confirmation from you developers.

Re: [PATCH] sequencer: fix memory leak if `todo_list_rearrange_squash()` failed

[Junio C Hamano]

Phillip Wood <phillip.wood123@gmail.com> writes:

> On 14/05/2025 14:53, Lidong Yan via GitGitGadget wrote:
>> From: Lidong Yan <502024330056@smail.nju.edu.cn>
>> In sequencer.c:todo_list_rearrange_squash, if it fails, memory
>> allocated in `next`, `tail`, `subjects` and `subject2item` will leak.
>> Jump to cleanup label before return could fix this leak problem.
>
> You could mention that you're adding the cleanup label.
>
> I suspect reaching this condition is a bug as well because we should
> only rearrange the todo list when the rebase starts. However I'm not
> 100% sure that it is impossible to trigger this condition so lets free
> it as you suggest. The code changes look good.

I wonder if there is a way (sort of using BUG("") but not as severe
as killing the program) for us to mark "we do not expect this code
path to be taken" and ask static analysis or fuzzers to disprove
such assertions.

The message being an error(), without a silent return doing nothing,
smells like a good enough sign, at least to me, that the original
author intended not to call this helper function on a list that was
already rearranged, so turning this into BUG("") may be something we
would want to consider doing in the longer term.

>> @@ -6626,8 +6627,8 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
>>   		}
>>     		if (is_fixup(item->command)) {
>> -			clear_commit_todo_item(&commit_todo);
>> -			return error(_("the script was already rearranged."));
>> +			ret = error(_("the script was already rearranged."));
>> +			goto cleanup;
>>   		}

Thanks.