On Sat, Aug 19, 2023 at 3:26 AM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>
> veth and vxcan need to make sure the ifindexes of the peer
> are not negative, core does not validate this.
>
> Using iproute2 with user-space-level checking removed:
>
> Before:
>
> # ./ip link add index 10 type veth peer index -1
> # ip link show
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
> link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
> 2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
> link/ether 52:54:00:74:b2:03 brd ff:ff:ff:ff:ff:ff
> 10: veth1@veth0: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
> link/ether 8a:90:ff:57:6d:5d brd ff:ff:ff:ff:ff:ff
> -1: veth0@veth1: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
> link/ether ae:ed:18:e6:fa:7f brd ff:ff:ff:ff:ff:ff
>
> Now:
>
> $ ./ip link add index 10 type veth peer index -1
> Error: ifindex can't be negative.
>
> This problem surfaced in net-next because an explicit WARN()
> was added, the root cause is older.
>
> Fixes: e6f8f1a739b6 ("veth: Allow to create peer link with given ifindex")
> Fixes: a8f820a380a2 ("can: add Virtual CAN Tunnel driver (vxcan)")
> Reported-by: syzbot+5ba06978f34abb058571@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
SGTM, I was not sure how to fix this myself ;)
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
