linux-kernel - Re: [PATCH v1 1/3] kallsyms: avoid hardcoding the buffer size

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Date:   Thu, 5 May 2022 16:46:33 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Miguel Ojeda <ojeda@...nel.org>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Changbin Du <changbin.du@...el.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH v1 1/3] kallsyms: avoid hardcoding the buffer size

On Thu, May 05, 2022 at 09:16:43PM +0200, Miguel Ojeda wrote:
> From: Boqun Feng <boqun.feng@...il.com>
> 
> This makes it easier to update the size later on.
> 
> Furthermore, a static assert is added to ensure both are updated
> when that happens. The relationship used is one that keeps the new
> size (512+1) close to the original buffer size (500).
> 
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> Co-developed-by: Miguel Ojeda <ojeda@...nel.org>
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> ---
>  scripts/kallsyms.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index 8caabddf817c..880c4404731b 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -27,8 +27,18 @@
>  
>  #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
>  
> +#define _stringify_1(x)	#x
> +#define _stringify(x)	_stringify_1(x)
> +
>  #define KSYM_NAME_LEN		128
>  
> +/* A substantially bigger size than the current maximum. */
> +#define KSYM_NAME_LEN_BUFFER	512
> +_Static_assert(
> +	KSYM_NAME_LEN_BUFFER == KSYM_NAME_LEN * 4,
> +	"Please keep KSYM_NAME_LEN_BUFFER in sync with KSYM_NAME_LEN"
> +);
> +
>  struct sym_entry {
>  	unsigned long long addr;
>  	unsigned int len;
> @@ -197,15 +207,15 @@ static void check_symbol_range(const char *sym, unsigned long long addr,
>  
>  static struct sym_entry *read_symbol(FILE *in)
>  {
> -	char name[500], type;
> +	char name[KSYM_NAME_LEN_BUFFER+1], type;
>  	unsigned long long addr;
>  	unsigned int len;
>  	struct sym_entry *sym;
>  	int rc;
>  
> -	rc = fscanf(in, "%llx %c %499s\n", &addr, &type, name);
> +	rc = fscanf(in, "%llx %c %" _stringify(KSYM_NAME_LEN_BUFFER) "s\n", &addr, &type, name);
>  	if (rc != 3) {
> -		if (rc != EOF && fgets(name, 500, in) == NULL)
> +		if (rc != EOF && fgets(name, KSYM_NAME_LEN_BUFFER + 1, in) == NULL)

No need to repeat the sizing:

	fgets(name, sizeof(name), in)

>  			fprintf(stderr, "Read error or end of file.\n");
>  		return NULL;
>  	}
> -- 
> 2.35.3
> 

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook