linux-kernel - Re: [PATCH] dm: Allow the use of escaped characters in str_field

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Message-ID: <d62bac7e-432e-23bc-3d4c-d860e164dcaf@redhat.com>
Date: Mon, 18 Nov 2024 11:38:05 +0100 (CET)
From: Mikulas Patocka <mpatocka@...hat.com>
To: Mohammed Anees <pvmohammedanees2003@...il.com>
cc: Alasdair Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...nel.org>, 
    dm-devel@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dm: Allow the use of escaped characters in
 str_field_delimit()



On Tue, 12 Nov 2024, Mohammed Anees wrote:

> Escape characters were not handled before, which could lead to
> unwanted issues. Some device-mapper names may contain backslashes (`\`)
> as valid characters and should not be treated as escape characters. Only
> escape characters followed directly by the separator are considered
> valid and need to be processed. After handling, the escape characters
> are removed to ensure the final string is correctly parsed without
> unwanted escape sequences which were used only for escaping.
> 
> Signed-off-by: Mohammed Anees <pvmohammedanees2003@...il.com>

Hi

Does anyone really need this? Is there some use case for using escape 
characters in device mapper names?

Mikulas

> ---
>  drivers/md/dm-init.c | 28 ++++++++++++++++++++++++----
>  1 file changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/md/dm-init.c b/drivers/md/dm-init.c
> index b37bbe762500..dad9d523f7fb 100644
> --- a/drivers/md/dm-init.c
> +++ b/drivers/md/dm-init.c
> @@ -88,13 +88,33 @@ static void __init dm_setup_cleanup(struct list_head *devices)
>  static char __init *str_field_delimit(char **str, char separator)
>  {
>  	char *s;
> +	/* This variable handles removing escape characters, which are
> +	 * only used to avoid the separator and aren't needed in the
> +	 * final string.
> +	 */
> +	char *write;
>  
> -	/* TODO: add support for escaped characters */
>  	*str = skip_spaces(*str);
> -	s = strchr(*str, separator);
> +	s = *str;
> +	write = *str;
> +
> +	/* Find the separator and handle escape character */
> +	while (*s) {
> +		/* If '\' is followed by the separator, skip '\' by
> +		 * incrementing s, write will then overwrite the
> +		 * escape character with the separator.
> +		 */
> +		if (*s == '\\' && *(s + 1) != '\0' && *(s + 1) == separator)
> +			s++;
> +		else if (*s == separator)
> +			break;
> +
> +		*write++ = *s++;
> +	}
> +
>  	/* Delimit the field and remove trailing spaces */
> -	if (s)
> -		*s = '\0';
> +	if (write)
> +		*write = '\0';
>  	*str = strim(*str);
>  	return s ? ++s : NULL;
>  }
> -- 
> 2.47.0
>