Re: [PATCH net v2] net: vxlan: prevent NULL deref in vxlan_xmit_one

[Ido Schimmel <idosch@idosch.org>]

On Wed, Nov 26, 2025 at 11:26:25AM +0100, Antoine Tenart wrote:
> Neither sock4 nor sock6 pointers are guaranteed to be non-NULL in
> vxlan_xmit_one, e.g. if the iface is brought down. This can lead to the
> following NULL dereference:
> 
>   BUG: kernel NULL pointer dereference, address: 0000000000000010
>   Oops: Oops: 0000 [#1] SMP NOPTI
>   RIP: 0010:vxlan_xmit_one+0xbb3/0x1580
>   Call Trace:
>    vxlan_xmit+0x429/0x610
>    dev_hard_start_xmit+0x55/0xa0
>    __dev_queue_xmit+0x6d0/0x7f0
>    ip_finish_output2+0x24b/0x590
>    ip_output+0x63/0x110
> 
> Mentioned commits changed the code path in vxlan_xmit_one and as a side
> effect the sock4/6 pointer validity checks in vxlan(6)_get_route were
> lost. Fix this by adding back checks.
> 
> Since both commits being fixed were released in the same version (v6.7)
> and are strongly related, bundle the fixes in a single commit.
> 
> Reported-by: Liang Li <liali@redhat.com>
> Fixes: 6f19b2c136d9 ("vxlan: use generic function for tunnel IPv4 route lookup")
> Fixes: 2aceb896ee18 ("vxlan: use generic function for tunnel IPv6 route lookup")
> Cc: Beniamino Galvani <b.galvani@gmail.com>
> Signed-off-by: Antoine Tenart <atenart@kernel.org>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Tested-by: Ido Schimmel <idosch@nvidia.com>

Tested using:

ip link add name vx0 up type vxlan id 10010 local 192.0.2.1 remote 198.51.100.1 dstport 4789
for i in $(seq 0 $(($(nproc) - 2))); do
	taskset -c $i mausezahn vx0 -a own -b 00:11:22:33:44:55 -c 0 -q &
done
taskset -c $(($(nproc) - 1)) bash -c "while true; do ip link set dev vx0 down && ip link set dev vx0 up; done"