Subject: Re: [PATCH iproute2] ip: Fix size_columns() invocation that passes a 32-bit quantity

From: Stephen Hemminger <[email-masked]>
Date: Mon, 27 Jun 2022 08:14:21 -0700

On Mon, 27 Jun 2022 15:20:01 +0200
Petr Machata <[email-masked]> wrote:

> In print_stats64(), the last size_columns() invocation passes number of
> carrier changes as one of the arguments. The value is decoded as a 32-bit
> quantity, but size_columns() expects a 64-bit one. This is undefined
> behavior.
> 
> The reason valgrind does not cite this is that the previous size_columns()
> invocations prime the ABI area used for the value transfer. When these
> other invocations are commented away, valgrind does complain that
> "conditional jump or move depends on uninitialised value", as would be
> expected.
> 
> Fixes: 49437375b6c1 ("ip: dynamically size columns when printing stats")
> Signed-off-by: Petr Machata <[email-masked]>
> ---
>  ip/ipaddress.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/ip/ipaddress.c b/ip/ipaddress.c
> index 5a3b1cae..8cd76073 100644
> --- a/ip/ipaddress.c
> +++ b/ip/ipaddress.c
> @@ -788,8 +788,9 @@ void print_stats64(FILE *fp, struct rtnl_link_stats64 *s,
>  				     s->tx_aborted_errors, s->tx_fifo_errors,
>  				     s->tx_window_errors,
>  				     s->tx_heartbeat_errors,
> -				     carrier_changes ?
> -				     rta_getattr_u32(carrier_changes) : 0);
> +				     (uint64_t)(carrier_changes ?
> +						rta_getattr_u32(carrier_changes)
> +						: 0));

Looks good, but would be clearer with a local temporary variable
which would eliminate the cast etc.