linux-hardening - Re: [PATCH] btrfs: Replace deprecated strncpy() with strscpy

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Message-ID: <20250225122828.GM5777@twin.jikos.cz>
Date: Tue, 25 Feb 2025 13:28:28 +0100
From: David Sterba <dsterba@...e.cz>
To: Thorsten Blum <thorsten.blum@...ux.dev>
Cc: Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
	David Sterba <dsterba@...e.com>, linux-hardening@...r.kernel.org,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: Replace deprecated strncpy() with strscpy_pad()

On Tue, Feb 25, 2025 at 10:29:49AM +0100, Thorsten Blum wrote:
> strncpy() is deprecated for NUL-terminated destination buffers. Use
> strscpy_pad() instead and don't zero-initialize the param array.
> 
> Compile-tested only.
> 
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
> ---
>  fs/btrfs/sysfs.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
> index 53b846d99ece..b941fb37776d 100644
> --- a/fs/btrfs/sysfs.c
> +++ b/fs/btrfs/sysfs.c
> @@ -1330,13 +1330,13 @@ MODULE_PARM_DESC(read_policy,
>  
>  int btrfs_read_policy_to_enum(const char *str, s64 *value_ret)
>  {
> -	char param[32] = { 0 };
> +	char param[32];
>  	char __maybe_unused *value_str;
>  
>  	if (!str || strlen(str) == 0)
>  		return 0;
>  
> -	strncpy(param, str, sizeof(param) - 1);
> +	strscpy_pad(param, str);

I don't think we need the padding, so strscpy is probably ok. We copy
input string to a temporary modifiable buffer and then match it against
a table, so the NUL termination is ok.