linux-kernel - Re: [PATCH v3 2/3] treewide: Switch memcpy() users of 'task->comm' to a more safer implementation

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Message-ID: <aBtSK5dFmtFXUaOE@pathway.suse.cz>
Date: Wed, 7 May 2025 14:29:46 +0200
From: Petr Mladek <pmladek@...e.com>
To: Bhupesh <bhupesh@...lia.com>
Cc: akpm@...ux-foundation.org, kernel-dev@...lia.com,
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
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Subject: Re: [PATCH v3 2/3] treewide: Switch memcpy() users of 'task->comm'
 to a more safer implementation

On Wed 2025-05-07 16:34:43, Bhupesh wrote:
> As Linus mentioned in [1], currently we have several memcpy() use-cases
> which use 'current->comm' to copy the task name over to local copies.
> For an example:
> 
>  ...
>  char comm[TASK_COMM_LEN];
>  memcpy(comm, current->comm, TASK_COMM_LEN);
>  ...
> 
> These should be modified so that we can later implement approaches
> to handle the task->comm's 16-byte length limitation (TASK_COMM_LEN)
> is a more modular way (follow-up patches do the same):
> 
>  ...
>  char comm[TASK_COMM_LEN];
>  memcpy(comm, current->comm, TASK_COMM_LEN);
>  comm[TASK_COMM_LEN - 1] = 0;
>  ...
> 
> The relevant 'memcpy()' users were identified using the following search
> pattern:
>  $ git grep 'memcpy.*->comm\>'
> 
> [1]. https://lore.kernel.org/all/CAHk-=wjAmmHUg6vho1KjzQi2=psR30+CogFd4aXrThr2gsiS4g@mail.gmail.com/
> 
> --- a/include/linux/coredump.h
> +++ b/include/linux/coredump.h
> @@ -53,7 +53,8 @@ extern void do_coredump(const kernel_siginfo_t *siginfo);
>  	do {	\
>  		char comm[TASK_COMM_LEN];	\
>  		/* This will always be NUL terminated. */ \
> -		memcpy(comm, current->comm, sizeof(comm)); \
> +		memcpy(comm, current->comm, TASK_COMM_LEN); \
> +		comm[TASK_COMM_LEN] = '\0'; \

I would expect that we replace this with a helper function/macro
which would do the right thing.

Why is get_task_comm() not used here, please?

>  		printk_ratelimited(Level "coredump: %d(%*pE): " Format "\n",	\

Also the name seems to be used for printing a debug information.
I would expect that we could use the bigger buffer here and print
the "full" name. Is this planed, please?

>  			task_tgid_vnr(current), (int)strlen(comm), comm, ##__VA_ARGS__);	\
>  	} while (0)	\
> diff --git a/include/trace/events/block.h b/include/trace/events/block.h
> index bd0ea07338eb..94a941ac2034 100644
> --- a/include/trace/events/block.h
> +++ b/include/trace/events/block.h
> @@ -214,6 +214,7 @@ DECLARE_EVENT_CLASS(block_rq,
>  		blk_fill_rwbs(__entry->rwbs, rq->cmd_flags);
>  		__get_str(cmd)[0] = '\0';
>  		memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
> +		__entry->comm[TASK_COMM_LEN - 1] = '\0';

Same for all other callers.

That said, I am not sure if the larger buffer is save in all situations.

>  	),

Best Regards,
Petr