Re: [PATCH] fix undefined behavior in ptrace

[Rich Felker <dalias@libc.org>]

On Wed, Jul 05, 2017 at 12:51:05AM +0300, Alexander Monakov wrote:
> ---
> On Tue, 4 Jul 2017, Rich Felker wrote:
> > Thoughts?
> 
> I'm not convinced it's a good idea, given that it's a Linux specific interface,
> and the manpage rather explicitly discourages passing fewer than four
> arguments.
> 
> Plus, handling SPARC-specific differences of argument counts for
> PTRACE_{GET,SET}{FP,}REGS would be annoying.
> 
> What makes sense is to retrieve the fifth argument only when needed:

Ah, okay. I'm fine with that. Thanks for clarifying.

>  src/linux/ptrace.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/src/linux/ptrace.c b/src/linux/ptrace.c
> index 83b8022b..a3f393d9 100644
> --- a/src/linux/ptrace.c
> +++ b/src/linux/ptrace.c
> @@ -7,14 +7,18 @@ long ptrace(int req, ...)
>  {
>  	va_list ap;
>  	pid_t pid;
> -	void *addr, *data, *addr2;
> +	void *addr, *data, *addr2 = 0;
>  	long ret, result;
>  
>  	va_start(ap, req);
>  	pid = va_arg(ap, pid_t);
>  	addr = va_arg(ap, void *);
>  	data = va_arg(ap, void *);
> -	addr2 = va_arg(ap, void *);
> +	/* PTRACE_{READ,WRITE}{DATA,TEXT} (16...19) are specific to SPARC. */
> +#ifdef PTRACE_READDATA
> +	if ((unsigned)req - PTRACE_READDATA < 4)
> +		addr2 = va_arg(ap, void *);
> +#endif
>  	va_end(ap);
>  
>  	if (req-1U < 3) data = &result;
> -- 
> 2.11.0

Applying.

Rich