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SubjectRe: [PATCH net-next 1/3] net: rework SIOCGSTAMP ioctl handling
On Wed, Aug 29, 2018 at 3:03 PM Arnd Bergmann <arnd@arndb.de> wrote:

> diff --git a/net/core/sock.c b/net/core/sock.c
> index 3730eb855095..df17bbfaca27 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -2897,37 +2897,31 @@ bool lock_sock_fast(struct sock *sk)
> }
> EXPORT_SYMBOL(lock_sock_fast);
>
> -int sock_get_timestamp(struct sock *sk, struct timeval __user *userstamp)
> +int sock_gettstamp(struct socket *sock, void __user *userstamp,
> + bool timeval, bool time32)
> {
> - struct timeval tv;
> -
> - sock_enable_timestamp(sk, SOCK_TIMESTAMP);
> - tv = ktime_to_timeval(sk->sk_stamp);
> - if (tv.tv_sec == -1)
> - return -ENOENT;
> - if (tv.tv_sec == 0) {
> - sk->sk_stamp = ktime_get_real();
> - tv = ktime_to_timeval(sk->sk_stamp);
> - }
> - return copy_to_user(userstamp, &tv, sizeof(tv)) ? -EFAULT : 0;
> -}
> -EXPORT_SYMBOL(sock_get_timestamp);

As I just learned, sparc64 uses a 32-bit suseconds_t, so this
function always leaked 32 bits of kernel stack data by copying
the padding bytes of 'tv' into user space.

Linux-4.11 and higher could avoid that with
CONFIG_GCC_PLUGIN_STRUCTLEAK, but older kernels
have been affected since socket timestamps were first added.

The same thing is probably true of many other interfaces
that pass a timeval.

> -int sock_get_timestampns(struct sock *sk, struct timespec __user *userstamp)
> -{
> - struct timespec ts;
> + struct sock *sk = sock->sk;
> + struct timespec64 ts;
>
> sock_enable_timestamp(sk, SOCK_TIMESTAMP);
> - ts = ktime_to_timespec(sk->sk_stamp);
> + ts = ktime_to_timespec64(sk->sk_stamp);
> if (ts.tv_sec == -1)
> return -ENOENT;
> if (ts.tv_sec == 0) {
> sk->sk_stamp = ktime_get_real();
> - ts = ktime_to_timespec(sk->sk_stamp);
> + ts = ktime_to_timespec64(sk->sk_stamp);
> }
> - return copy_to_user(userstamp, &ts, sizeof(ts)) ? -EFAULT : 0;
> +
> + if (timeval)
> + ts.tv_nsec /= 1000;
> +#ifdef CONFIG_COMPAT_32BIT_TIME
> + if (time32)
> + return put_old_timespec32(&ts, userstamp);
> +#endif
> +
> + return put_timespec64(&ts, userstamp);
> }

My new implementation is worse here: it no longer leaks stack
data, but since we now write a big-endian 64-bit microseconds
value, the microseconds are in the wrong place and will
be interpreted as zero by user space...

I'll also have to revisit a few other similar patches I did for
y2038, to figure out what they should do on sparc64.

Arnd

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