netdev - Re: [PATCH] can: bcm: fix infoleak in struct bcm_msg

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Date:   Sun, 13 Jun 2021 11:51:34 +0200
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Norbert Slusarek <nslusarek@....net>
Cc:     mkl@...gutronix.de, davem@...emloft.net, kuba@...nel.org,
        linux-can@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] can: bcm: fix infoleak in struct bcm_msg_head



On 12.06.21 23:09, Norbert Slusarek wrote:
> From: Norbert Slusarek <nslusarek@....net>
> Date: Sat, 12 Jun 2021 22:18:54 +0200
> Subject: [PATCH] can: bcm: fix infoleak in struct bcm_msg_head
> 
> On 64-bit systems, struct bcm_msg_head has an added padding of 4 bytes between
> struct members count and ival1. Even though all struct members are initialized,
> the 4-byte hole will contain data from the kernel stack. This patch zeroes out
> struct bcm_msg_head before usage, preventing infoleaks to userspace.
> 
> Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol")
> Signed-off-by: Norbert Slusarek <nslusarek@....net>

Acked-by: Oliver Hartkopp <socketcan@...tkopp.net>

Thanks Norbert!

Yes, when this data structure was created in 2003 either 64 bit machines 
were far away for me and infoleaks were not a hot topic like today.

Would be interesting to check where data structures are used in the 
Linux UAPI that became an infoleak in the 32-to-64-bit compilation 
transistion.

Thanks for the heads up!

Best regards,
Oliver

> 
> ---
>   net/can/bcm.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/net/can/bcm.c b/net/can/bcm.c
> index 909b9e684e04..b03062f84fe7 100644
> --- a/net/can/bcm.c
> +++ b/net/can/bcm.c
> @@ -402,6 +402,7 @@ static enum hrtimer_restart bcm_tx_timeout_handler(struct hrtimer *hrtimer)
>                  if (!op->count && (op->flags & TX_COUNTEVT)) {
> 
>                          /* create notification to user */
> +                       memset(&msg_head, 0, sizeof(msg_head));
>                          msg_head.opcode  = TX_EXPIRED;
>                          msg_head.flags   = op->flags;
>                          msg_head.count   = op->count;
> @@ -439,6 +440,7 @@ static void bcm_rx_changed(struct bcm_op *op, struct canfd_frame *data)
>          /* this element is not throttled anymore */
>          data->flags &= (BCM_CAN_FLAGS_MASK|RX_RECV);
> 
> +       memset(&head, 0, sizeof(head));
>          head.opcode  = RX_CHANGED;
>          head.flags   = op->flags;
>          head.count   = op->count;
> @@ -560,6 +562,7 @@ static enum hrtimer_restart bcm_rx_timeout_handler(struct hrtimer *hrtimer)
>          }
> 
>          /* create notification to user */
> +       memset(&msg_head, 0, sizeof(msg_head));
>          msg_head.opcode  = RX_TIMEOUT;
>          msg_head.flags   = op->flags;
>          msg_head.count   = op->count;
> --
> 2.30.2
>