[apparmor] [PATCH] parser: Quiet valgrind false positive

[Seth Arnold]

On Wed, Feb 05, 2014 at 01:22:42PM -0500, Tyler Hicks wrote:
> strlen() assumes that it can read an entire word but when a char array
> array does not end on a word boundary, it reads past the end of the
> array. This results in the following valgrind warning:
> 
>  Invalid read of size 4
>     at 0x40A162: yylex() (parser_lex.l:277)
>     by 0x40FA14: yyparse() (parser_yacc.c:1487)
>     by 0x40C5B9: process_profile(int, char const*) (parser_main.c:1003)
>     by 0x404074: main (parser_main.c:1340)
>   Address 0x578d870 is 16 bytes inside a block of size 18 alloc'd
>     at 0x4C2A420: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
>     by 0x53E31C9: strdup (strdup.c:42)
>     by 0x40A145: yylex() (parser_lex.l:276)
>     by 0x40FA14: yyparse() (parser_yacc.c:1487)
>     by 0x40C5B9: process_profile(int, char const*) (parser_main.c:1003)
>     by 0x404074: main (parser_main.c:1340)
> 
> This patch quiets the warning by not using strlen(). This can be done
> because yyleng already contains the length of string.
> 
> Signed-off-by: Tyler Hicks <tyhicks at canonical.com>

Very nice, thanks.

Acked-by: Seth Arnold <seth.arnold at canonical.com>

> ---
>  parser/parser_lex.l | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/parser/parser_lex.l b/parser/parser_lex.l
> index 1938297..1b60053 100644
> --- a/parser/parser_lex.l
> +++ b/parser/parser_lex.l
> @@ -273,8 +273,7 @@ LT_EQUAL	<=
>  
>  <INCLUDE>{
>  	(\<([^\> \t\n]+)\>|\"([^\" \t\n]+)\")	{	/* <filename> */
> -		char *filename = strdup(yytext);
> -		filename[strlen(filename) - 1] = '\0';
> +		char *filename = strndup(yytext, yyleng - 1);
>  		include_filename(filename + 1, *filename == '<');
>  		free(filename);
>  		yy_pop_state();
> -- 
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