linux-hardening - Re: [PATCH] udf: replace deprecated strncpy/strcpy with strscpy

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Message-ID: <20240402132420.aalwgi6gdnmrj3ep@quack3>
Date: Tue, 2 Apr 2024 15:24:20 +0200
From: Jan Kara <jack@...e.cz>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Jan Kara <jack@...e.com>, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] udf: replace deprecated strncpy/strcpy with strscpy

On Mon 01-04-24 20:01:51, Justin Stitt wrote:
> strncpy() is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces. Also replace an instance of strcpy() which is also
> deprecated.
> 
> s_volume_ident is a NUL-terminated string which is evident from its
> usage in udf_debug:
> |	udf_debug("volIdent[] = '%s'\n", UDF_SB(sb)->s_volume_ident);
> 
> s_volume_ident should also be NUL-padded as it is copied out to
> userspace:
> |	if (copy_to_user((char __user *)arg,
> |				UDF_SB(inode->i_sb)->s_volume_ident, 32))
> |		return -EFAULT;
> 
> Considering the above, a suitable replacement is `strscpy_pad` [2] due
> to the fact that it guarantees both NUL-termination and NUL-padding on
> the destination buffer.
> 
> To simplify the code, let's use the new 2-argument version of
> strscpy_pad() introduced in Commit e6584c3964f2f ("string: Allow
> 2-argument strscpy()"). Also zero-allocate @outstr so we can safely use
> a non-@ret length argument. This is just in case udf_dstrCS0toChar()
> doesn't include the NUL-byte in its return length, we won't truncate
> @outstr or write garbage bytes either.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Thanks! Added to my tree.

								Honza

> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>  fs/udf/super.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/udf/super.c b/fs/udf/super.c
> index 2217f7ed7a49..77d32fe14434 100644
> --- a/fs/udf/super.c
> +++ b/fs/udf/super.c
> @@ -895,7 +895,7 @@ static int udf_load_pvoldesc(struct super_block *sb, sector_t block)
>  	int ret;
>  	struct timestamp *ts;
>  
> -	outstr = kmalloc(128, GFP_KERNEL);
> +	outstr = kzalloc(128, GFP_KERNEL);
>  	if (!outstr)
>  		return -ENOMEM;
>  
> @@ -921,11 +921,11 @@ static int udf_load_pvoldesc(struct super_block *sb, sector_t block)
>  
>  	ret = udf_dstrCS0toChar(sb, outstr, 31, pvoldesc->volIdent, 32);
>  	if (ret < 0) {
> -		strcpy(UDF_SB(sb)->s_volume_ident, "InvalidName");
> +		strscpy_pad(UDF_SB(sb)->s_volume_ident, "InvalidName");
>  		pr_warn("incorrect volume identification, setting to "
>  			"'InvalidName'\n");
>  	} else {
> -		strncpy(UDF_SB(sb)->s_volume_ident, outstr, ret);
> +		strscpy_pad(UDF_SB(sb)->s_volume_ident, outstr);
>  	}
>  	udf_debug("volIdent[] = '%s'\n", UDF_SB(sb)->s_volume_ident);
>  
> 
> ---
> base-commit: 928a87efa42302a23bb9554be081a28058495f22
> change-id: 20240401-strncpy-fs-udf-super-c-983457eb4ac3
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR