linux-kernel - Re: [PATCH] Avoid potential NULL deref in scripts/genksyms/lex.l

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Date:	Sun, 24 Jun 2007 14:58:37 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jesper Juhl <jesper.juhl@...il.com>
Cc:	Richard Henderson <rth@...u.edu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Avoid potential NULL deref in scripts/genksyms/lex.l

On Sun, 24 Jun 2007 23:40:03 +0200 Jesper Juhl <jesper.juhl@...il.com> wrote:

> strchr() returns NULL in case the string is not found and if that 
> happens we risk dereferencing a NULL pointer. It never hurts to 
> check for that condition and exit normally with an error rather 
> than crashing.
> 
> (no, the indentation is not according to CodingStyle, it's simply 
>  following whatever else is in that file)
> 
> 
> Signed-off-by: Jesper Juhl <jesper.juhl@...il.com>
> ---
> 
>  scripts/genksyms/lex.l        |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/scripts/genksyms/lex.l b/scripts/genksyms/lex.l
> index 5e544a0..28edc0c 100644
> --- a/scripts/genksyms/lex.l
> +++ b/scripts/genksyms/lex.l
> @@ -154,6 +154,8 @@ repeat:
>  
>        file = strchr(yytext, '\"')+1;
>        e = strchr(file, '\"');

If `file' can be null we'd have oopsed here.

> +      if (!file || !e)
> +	exit(1);
>        *e = '\0';
>        cur_filename = memcpy(xmalloc(e-file+1), file, e-file+1);
>        cur_line = atoi(yytext+2);

I don't think the bug which you're fixing can occur:

^#[ \t]+{INT}[ \t]+\"[^\"\n]+\".*\n     return FILENAME;

has anyone reported crashes in there?
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