linux-kernel - Re: [PATCH v4] scsi: target: transform strncpy into strscpy

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Message-ID: <20250405162548.310dea37@pumpkin>
Date: Sat, 5 Apr 2025 16:25:48 +0100
From: David Laight <david.laight.linux@...il.com>
To: Baris Can Goral <goralbaris@...il.com>
Cc: martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
 target-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
 skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linux.dev
Subject: Re: [PATCH v4] scsi: target: transform strncpy into strscpy

On Sat,  5 Apr 2025 17:36:47 +0300
Baris Can Goral <goralbaris@...il.com> wrote:

> The strncpy() function is actively dangerous to use since it may not
> NULL-terminate the destination string,resulting in potential memory
> content exposures, unbounded reads, or crashes.
> 
> Link:https://github.com/KSPP/linux/issues/90
> Signed-off-by: Baris Can Goral <goralbaris@...il.com>
> ---
> Changes from v4:
> 	-Description added
> 	-User name corrected
> 	-formatting issues.
> 	-commit name changed
>  drivers/target/target_core_configfs.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c
> index c40217f44b1b..5c0b74e76be2 100644
> --- a/drivers/target/target_core_configfs.c
> +++ b/drivers/target/target_core_configfs.c
> @@ -143,7 +143,7 @@ static ssize_t target_core_item_dbroot_store(struct config_item *item,
>  	}
>  	filp_close(fp, NULL);
>  
> -	strncpy(db_root, db_root_stage, read_bytes);
> +	strscpy(db_root, db_root_stage, read_bytes);
>  	pr_debug("Target_Core_ConfigFS: db_root set to %s\n", db_root);

That code is broken, it reads:
	read_bytes = snprintf(db_root_stage, DB_ROOT_LEN, "%s", page);
	if (!read_bytes)
		goto unlock;

	if (db_root_stage[read_bytes - 1] == '\n')
		db_root_stage[read_bytes - 1] = '\0';

	/* validate new db root before accepting it */
	fp = filp_open(db_root_stage, O_RDONLY, 0);
	if (IS_ERR(fp)) {
		pr_err("db_root: cannot open: %s\n", db_root_stage);
		goto unlock;
	}
	if (!S_ISDIR(file_inode(fp)->i_mode)) {
		filp_close(fp, NULL);
		pr_err("db_root: not a directory: %s\n", db_root_stage);
		goto unlock;
	}
	filp_close(fp, NULL);

	strncpy(db_root, db_root_stage, read_bytes);
	pr_debug("Target_Core_ConfigFS: db_root set to %s\n", db_root);

	r = read_bytes;

unlock:
	mutex_unlock(&target_devices_lock);
	return r;

'Really nasty (tm)' things happen if 'page' is too long.

	David

>  
>  	r = read_bytes;
> @@ -3664,7 +3664,7 @@ static void target_init_dbroot(void)
>  	}
>  	filp_close(fp, NULL);
>  
> -	strncpy(db_root, db_root_stage, DB_ROOT_LEN);
> +	strscpy(db_root, db_root_stage, DB_ROOT_LEN);
>  	pr_debug("Target_Core_ConfigFS: db_root set to %s\n", db_root);
>  }
>