Re: [musl] [PATCH] clone: Return EINVAL for null stack

[Rich Felker <dalias@libc.org>]

On Tue, Aug 02, 2022 at 12:30:36PM +0100, Tudor Cretu wrote:
> This change aligns the clone wrapper with the man page. If the stack is
> null, clone sets errno to EINVAL, instead of throwing a segmentation fault.
> ---
>  src/linux/clone.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/src/linux/clone.c b/src/linux/clone.c
> index 8c1af7d3..43a6803b 100644
> --- a/src/linux/clone.c
> +++ b/src/linux/clone.c
> @@ -1,4 +1,5 @@
>  #define _GNU_SOURCE
> +#include <errno.h>
>  #include <stdarg.h>
>  #include <unistd.h>
>  #include <sched.h>
> @@ -11,6 +12,10 @@ int clone(int (*func)(void *), void *stack, int flags, void *arg, ...)
>  	pid_t *ptid, *ctid;
>  	void  *tls;
>  
> +	if (!stack) {
> +		return __syscall_ret(-EINVAL);
> +	}
> +
>  	va_start(ap, arg);
>  	ptid = va_arg(ap, pid_t *);
>  	tls  = va_arg(ap, void *);
> -- 
> 2.25.1

This is probably okay, but there's also a bigger discussion to be had
here about what to do about clone() -- deciding what the contract is
for what usage can be supported, and possibly making the rest produce
errors like the above. There's also a matter of the current very-wrong
use of va_arg for variadic arguments that might not exist, and which
probably *can't* exist in any valid application usage. This came up
before as part of the mt-fork work, but was basically deferred
indefinitely...

Rich