[PATCH net v2] net: dsa: Check existence of .port_mdb_add callback before calling it

From: Chen-Yu Tsai
Date: Tue Aug 06 2019 - 03:53:42 EST

From: Chen-Yu Tsai <wens@xxxxxxxx>

With the recent addition of commit 75dad2520fc3 ("net: dsa: b53: Disable
all ports on setup"), users of b53 (BCM53125 on Lamobo R1 in my case)
are forced to use the dsa subsystem to enable the switch, instead of
having it in the default transparent "forward-to-all" mode.

The b53 driver does not support mdb bitmap functions. However the dsa
layer does not check for the existence of the .port_mdb_add callback
before actually using it. This results in a NULL pointer dereference,
as shown in the kernel oops below.

The other functions seem to be properly guarded. Do the same for
.port_mdb_add in dsa_switch_mdb_add_bitmap() as well.

b53 is not the only driver that doesn't support mdb bitmap functions.
Others include bcm_sf2, dsa_loop, lantiq_gswip, mt7530, mv88e6060,
qca8k, realtek-smi, and vitesse-vsc73xx.

8<--- cut here ---
Unable to handle kernel NULL pointer dereference at virtual address 00000000
pgd = (ptrval)
[00000000] *pgd=00000000
Internal error: Oops: 80000005 [#1] SMP ARM
Modules linked in: rtl8xxxu rtl8192cu rtl_usb rtl8192c_common rtlwifi mac80211 cfg80211
CPU: 1 PID: 134 Comm: kworker/1:2 Not tainted 5.3.0-rc1-00247-gd3519030752a #1
Hardware name: Allwinner sun7i (A20) Family
Workqueue: events switchdev_deferred_process_work
PC is at 0x0
LR is at dsa_switch_event+0x570/0x620
pc : [<00000000>] lr : [<c08533ec>] psr: 80070013
sp : ee871db8 ip : 00000000 fp : ee98d0a4
r10: 0000000c r9 : 00000008 r8 : ee89f710
r7 : ee98d040 r6 : ee98d088 r5 : c0f04c48 r4 : ee98d04c
r3 : 00000000 r2 : ee89f710 r1 : 00000008 r0 : ee98d040
Flags: Nzcv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
Control: 10c5387d Table: 6deb406a DAC: 00000051
Process kworker/1:2 (pid: 134, stack limit = 0x(ptrval))
Stack: (0xee871db8 to 0xee872000)
1da0: ee871e14 103ace2d
1dc0: 00000000 ffffffff 00000000 ee871e14 00000005 00000000 c08524a0 00000000
1de0: ffffe000 c014bdfc c0f04c48 ee871e98 c0f04c48 ee9e5000 c0851120 c014bef0
1e00: 00000000 b643aea2 ee9b4068 c08509a8 ee2bf940 ee89f710 ee871ecb 00000000
1e20: 00000008 103ace2d 00000000 c087e248 ee29c868 103ace2d 00000001 ffffffff
1e40: 00000000 ee871e98 00000006 00000000 c0fb2a50 c087e2d0 ffffffff c08523c4
1e60: ffffffff c014bdfc 00000006 c0fad2d0 ee871e98 ee89f710 00000000 c014c500
1e80: 00000000 ee89f3c0 c0f04c48 00000000 ee9e5000 c087dfb4 ee9e5000 00000000
1ea0: ee89f710 ee871ecb 00000001 103ace2d 00000000 c0f04c48 00000000 c087e0a8
1ec0: 00000000 efd9a3e0 0089f3c0 103ace2d ee89f700 ee89f710 ee9e5000 00000122
1ee0: 00000100 c087e130 ee89f700 c0fad2c8 c1003ef0 c087de4c 2e928000 c0fad2ec
1f00: c0fad2ec ee839580 ef7a62c0 ef7a9400 00000000 c087def8 c0fad2ec c01447dc
1f20: ef315640 ef7a62c0 00000008 ee839580 ee839594 ef7a62c0 00000008 c0f03d00
1f40: ef7a62d8 ef7a62c0 ffffe000 c0145b84 ffffe000 c0fb2420 c0bfaa8c 00000000
1f60: ffffe000 ee84b600 ee84b5c0 00000000 ee870000 ee839580 c0145b40 ef0e5ea4
1f80: ee84b61c c014a6f8 00000001 ee84b5c0 c014a5b0 00000000 00000000 00000000
1fa0: 00000000 00000000 00000000 c01010e8 00000000 00000000 00000000 00000000
1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
1fe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000
[<c08533ec>] (dsa_switch_event) from [<c014bdfc>] (notifier_call_chain+0x48/0x84)
[<c014bdfc>] (notifier_call_chain) from [<c014bef0>] (raw_notifier_call_chain+0x18/0x20)
[<c014bef0>] (raw_notifier_call_chain) from [<c08509a8>] (dsa_port_mdb_add+0x48/0x74)
[<c08509a8>] (dsa_port_mdb_add) from [<c087e248>] (__switchdev_handle_port_obj_add+0x54/0xd4)
[<c087e248>] (__switchdev_handle_port_obj_add) from [<c087e2d0>] (switchdev_handle_port_obj_add+0x8/0x14)
[<c087e2d0>] (switchdev_handle_port_obj_add) from [<c08523c4>] (dsa_slave_switchdev_blocking_event+0x94/0xa4)
[<c08523c4>] (dsa_slave_switchdev_blocking_event) from [<c014bdfc>] (notifier_call_chain+0x48/0x84)
[<c014bdfc>] (notifier_call_chain) from [<c014c500>] (blocking_notifier_call_chain+0x50/0x68)
[<c014c500>] (blocking_notifier_call_chain) from [<c087dfb4>] (switchdev_port_obj_notify+0x44/0xa8)
[<c087dfb4>] (switchdev_port_obj_notify) from [<c087e0a8>] (switchdev_port_obj_add_now+0x90/0x104)
[<c087e0a8>] (switchdev_port_obj_add_now) from [<c087e130>] (switchdev_port_obj_add_deferred+0x14/0x5c)
[<c087e130>] (switchdev_port_obj_add_deferred) from [<c087de4c>] (switchdev_deferred_process+0x64/0x104)
[<c087de4c>] (switchdev_deferred_process) from [<c087def8>] (switchdev_deferred_process_work+0xc/0x14)
[<c087def8>] (switchdev_deferred_process_work) from [<c01447dc>] (process_one_work+0x218/0x50c)
[<c01447dc>] (process_one_work) from [<c0145b84>] (worker_thread+0x44/0x5bc)
[<c0145b84>] (worker_thread) from [<c014a6f8>] (kthread+0x148/0x150)
[<c014a6f8>] (kthread) from [<c01010e8>] (ret_from_fork+0x14/0x2c)
Exception stack(0xee871fb0 to 0xee871ff8)
1fa0: 00000000 00000000 00000000 00000000
1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
1fe0: 00000000 00000000 00000000 00000000 00000013 00000000
Code: bad PC value
---[ end trace 1292c61abd17b130 ]---

[<c08533ec>] (dsa_switch_event) from [<c014bdfc>] (notifier_call_chain+0x48/0x84)
corresponds to

$ arm-linux-gnueabihf-addr2line -C -i -e vmlinux c08533ec

linux/net/dsa/switch.c:156
linux/net/dsa/switch.c:178
linux/net/dsa/switch.c:328

Fixes: e6db98db8a95 ("net: dsa: add switch mdb bitmap functions")
Signed-off-by: Chen-Yu Tsai <wens@xxxxxxxx>
---
Changes since v1:

- Moved the check to the beginning of dsa_switch_mdb_add()

Looks like we could also move the ops check out of
dsa_switch_mdb_prepare_bitmap(), though I suppose keeping the code the
way it is now is clearer.

---
net/dsa/switch.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/net/dsa/switch.c b/net/dsa/switch.c
index 4ec5b7f85d51..231af5268656 100644
--- a/net/dsa/switch.c
+++ b/net/dsa/switch.c
@@ -164,6 +164,9 @@ static int dsa_switch_mdb_add(struct dsa_switch *ds,
struct switchdev_trans *trans = info->trans;
int port;

+ if (!ds->ops->port_mdb_add)
+ return -EOPNOTSUPP;
+
/* Build a mask of Multicast group members */
bitmap_zero(ds->bitmap, ds->num_ports);
if (ds->index == info->sw_index)
--
2.20.1