On 11/18/19 9:49 PM, Oliver Hartkopp wrote:
On 18/11/2019 21.29, Marc Kleine-Budde wrote:
On 11/18/19 9:25 PM, Oliver Hartkopp wrote:
IMPORTANT: if you fix the bug, please add the following tag to the commit:
BUG: KMSAN: uninit-value in can_receive+0x23c/0x5e0 net/can/af_can.c:649
CPU: 1 PID: 3490 Comm: syz-executor.2 Not tainted 5.4.0-rc5+ #0
In line 649 of 5.4.0-rc5+ we can find a while() statement:
can_skb_prv(skb)->skbcnt = atomic_inc_return(&skbcounter);
In linux/include/linux/can/skb.h we see:
static inline struct can_skb_priv *can_skb_prv(struct sk_buff *skb)
return (struct can_skb_priv *)(skb->head);
IMO accessing can_skb_prv(skb)->skbcnt at this point is a valid
operation which has no uninitialized value.
Can this probably be a false positive of KMSAN?
The packet is injected via the packet socket into the kernel. Where does
skb->head point to in this case? When the skb is a proper
kernel-generated skb containing a CAN-2.0 or CAN-FD frame skb->head is
maybe properly initialized?
The packet is either received via vcan or vxcan which checks via
can_dropped_invalid_skb() if we have a valid ETH_P_CAN type skb.
According to the call stack it's injected into the kernel via a packet
socket and not via v(x)can.
We additionally might think about introducing a check whether we have a
can_skb_reserve() created skbuff.
But even if someone forged a skbuff without this reserved space the
access to can_skb_prv(skb)->skbcnt would point into some CAN frame
content - which is still no access to uninitialized content, right?