rmnet_map_deaggregate() allocates each sub-frame with alloc_skb() and leaves skb->dev NULL. __rmnet_map_ingress_handler() assigns skb->dev = ep->egress_dev only on the data path, but a MAP command frame is dispatched to rmnet_map_command() before that, so rmnet_map_send_ack() runs netif_tx_lock(skb->dev) on a NULL device. An unprivileged user reaches this by unsharing a user+net namespace, creating an rmnet link over a tap device with INGRESS_DEAGGREGATION and INGRESS_MAP_COMMANDS, and writing an aggregated frame carrying a flow-control command to the tap fd. Assign port->dev before dispatch: the command was received on the real device tracked by port->dev and the ACK must egress on that same device. The non-deaggregated path already has skb->dev == real_dev. BUG: KASAN: null-ptr-deref in _raw_spin_lock (kernel/locking/spinlock.c:158) Write of size 4 at addr 00000000000004b4 by task exploit/144 Call Trace: _raw_spin_lock (kernel/locking/spinlock.c:158) netif_tx_lock (net/sched/sch_generic.c:497) rmnet_map_command (drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c:67) rmnet_rx_handler (drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c:125) __netif_receive_skb_core.constprop.0 (net/core/dev.c:6103) ... __netif_receive_skb_one_core (net/core/dev.c:6214) netif_receive_skb (net/core/dev.c:6474) tun_get_user (drivers/net/tun.c:1966) tun_chr_write_iter (drivers/net/tun.c:2012) vfs_write (fs/read_write.c:687) ksys_write (fs/read_write.c:739) do_syscall_64 (arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) Kernel panic - not syncing: Fatal exception in interrupt Fixes: 378e25357ac7 ("net: qualcomm: rmnet: Remove unnecessary device assignment") Reported-by: co+4638111fe2a12980@bugs.sh Closes: https://lore.kernel.org/netdev/ijg79FFMfIvKJbivdJEKvTO90Q9dTvyBkJck@bugs.sh/T/#u Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Xiang Mei --- drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c index add0f5ade2e6..3944925566fc 100644 --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c @@ -79,6 +79,8 @@ void rmnet_map_command(struct sk_buff *skb, struct rmnet_port *port) unsigned char command_name; unsigned char rc = 0; + skb->dev = port->dev; + /* Command data immediately follows the MAP header */ cmd = (struct rmnet_map_control_command *)(map_header + 1); command_name = cmd->command_name; -- 2.43.0