Re: [PATCH] NFS: nfsroot: replace strlcat() with snprintf()

[David Laight <david.laight.linux@gmail.com>]

On Fri, 14 Aug 2026 00:28:45 -0700
Mariia Nikitash <mariianikitash@google.com> wrote:

> In preparation for removing the deprecated strlcat() API[1], replace its
> uses in root_nfs_cat() with snprintf().
> 
> Build the separator and source string in a single call using the
> remaining space in the destination buffer. snprintf() returns the length
> it would have written excluding the terminating NUL, so comparing the
> return value against the remaining buffer space preserves the existing
> truncation check.
> 
> Link: https://github.com/KSPP/linux/issues/370 [1]
> Signed-off-by: Mariia Nikitash <mariianikitash@google.com>
> ---
>  fs/nfs/nfsroot.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/nfs/nfsroot.c b/fs/nfs/nfsroot.c
> index 432612d22437..e951fe731679 100644
> --- a/fs/nfs/nfsroot.c
> +++ b/fs/nfs/nfsroot.c
> @@ -173,12 +173,12 @@ static int __init root_nfs_cat(char *dest, const char *src,
>  			       const size_t destlen)
>  {
>  	size_t len = strlen(dest);
> +	size_t remaining = destlen - len;
> +	const char *sep = "";
>  
>  	if (len && dest[len - 1] != ',')
> -		if (strlcat(dest, ",", destlen) >= destlen)
> -			return -1;
> -
> -	if (strlcat(dest, src, destlen) >= destlen)
> +		sep = ",";
> +	if (snprintf(dest + len, remaining, "%s%s", sep, src) >= remaining)
>  		return -1;

I think I'd have gone for:
	size_t len = strlen(dest);
	if (len && dest[len - 1] != ',' && ++len < destlen)
		dest[len - 1] = ',';
	if (strscpy(dest + len, src, destlen - len) < 0)
		return -1;

Although it would be better as an 'add_option()' function.
I suspect the it used to be just strcat().
(similarly for root_nfs_copy() which is a pointless wrapper on strscpy()).

Much more worth while would be fixing the sprintf() for NFS_ROOT.

David

>  	return 0;
>  }