Re: [PATCH] sunrpc: Fix incorrect parsing of expiry time

[NeilBrown]

On Wed, 08 Mar 2023, Jerry Zhang wrote:
> The expiry time field is mean to be expressed in seconds since boot.

Correct.

> The get_expiry() function parses a relative time value in seconds.

Incorrect.  It parses and absoulte wall-clock time.

NeilBrown

> In order to get the absolute time of seconds since boot that the given
> message will expire, the right thing is to add seconds_since_boot()
> to the given relative value.
> 
> Previously this logic was subtracting boot.tv_sec from the relative
> value, which was causing some confusing behavior. The return type of
> time64_t could possibly underflow if time since boot is greater than
> the passed in relative argument. Also several checks in nfs code compare
> the return value to 0 to indicate failure, and this could spuriously
> be tripped if seconds since boot happened to match the argument.
> 
> Fixes: c5b29f885afe ("sunrpc: use seconds since boot in expiry cache")
> Signed-off-by: Jerry Zhang <Jerry@xxxxxxxxxx>
> ---
>  include/linux/sunrpc/cache.h | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/include/linux/sunrpc/cache.h b/include/linux/sunrpc/cache.h
> index ec5a555df96f..b96b1319c93d 100644
> --- a/include/linux/sunrpc/cache.h
> +++ b/include/linux/sunrpc/cache.h
> @@ -301,16 +301,14 @@ static inline int get_time(char **bpp, time64_t *time)
>  }
>  
>  static inline time64_t get_expiry(char **bpp)
>  {
>  	time64_t rv;
> -	struct timespec64 boot;
>  
>  	if (get_time(bpp, &rv))
>  		return 0;
>  	if (rv < 0)
>  		return 0;
> -	getboottime64(&boot);
> -	return rv - boot.tv_sec;
> +	return rv + seconds_since_boot();
>  }
>  
>  #endif /*  _LINUX_SUNRPC_CACHE_H_ */
> -- 
> 2.37.3
> 
>