[CRIU] [PATCH] compel: Do not loose sign of result in compat syscall

[Andrey Vagin]

On Mon, Oct 30, 2017 at 05:57:31PM +0300, Cyrill Gorcunov wrote:
> From: Cyrill Gorcunov <gorcunov at virtuozzo.com>
> 
> Regs are present in unsigned format so convert them
> into signed first to provide results.
> 
> In particular if memfd_create syscall failed we won't
> notice -ENOMEM error but rather treat it as unsigned
> hex value
> 
>  | (05.303002) Putting parasite blob into 0x7f1c6ffe0000->0xfffffff4
>  | (05.303234) Putting tsock into pid 42773
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov at virtuozzo.com>
> ---
> 
> Travis is running by now https://travis-ci.org/cyrillos/criu/builds/294898355
> 
>  compel/arch/x86/src/lib/infect.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/compel/arch/x86/src/lib/infect.c b/compel/arch/x86/src/lib/infect.c
> index 9c919e64ef13..ac5f8b05e768 100644
> --- a/compel/arch/x86/src/lib/infect.c
> +++ b/compel/arch/x86/src/lib/infect.c
> @@ -293,9 +293,10 @@ int compel_syscall(struct parasite_ctl *ctl, int nr, long *ret,
>  		unsigned long arg6)
>  {
>  	user_regs_struct_t regs = ctl->orig.regs;
> +	bool native = user_regs_native(&regs);
>  	int err;
>  
> -	if (user_regs_native(&regs)) {
> +	if (native) {
>  		user_regs_struct64 *r = &regs.native;
>  
>  		r->ax  = (uint64_t)nr;
> @@ -321,7 +322,9 @@ int compel_syscall(struct parasite_ctl *ctl, int nr, long *ret,
>  		err = compel_execute_syscall(ctl, &regs, code_int_80);
>  	}
>  
> -	*ret = get_user_reg(&regs, ax);
> +	*ret = native ?
> +		(long)get_user_reg(&regs, ax) :
> +		(int)get_user_reg(&regs, ax);

mmap() can return a negative value, but it will be actually a valid
address and we have to return it without modifications. How does this
code handle this case?

>  	return err;
>  }
>  
> -- 
> 2.7.5
>