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Message-ID: <ee5bdf78-1955-4e7f-96e0-b62c0a977e18@hartkopp.net>
Date: Wed, 24 Sep 2025 15:38:59 +0200
From: Oliver Hartkopp <socketcan@...tkopp.net>
To: Vincent Mailhol <mailhol@...nel.org>
Cc: syzbot@...ts.linux.dev, syzkaller-bugs@...glegroups.com,
syzbot ci <syzbot+ci284feacb80736eb0@...kaller.appspotmail.com>,
biju.das.jz@...renesas.com, davem@...emloft.net, geert@...der.be,
kernel@...gutronix.de, kuba@...nel.org, linux-can@...r.kernel.org,
mkl@...gutronix.de, netdev@...r.kernel.org, stefan.maetje@....eu,
stephane.grosjean@...-networks.com, zhao.xichao@...o.com
Subject: Re: [syzbot ci] Re: pull-request: can-next 2025-09-24
On 24.09.25 15:31, Vincent Mailhol wrote:
> On 24/09/2025 at 22:18, Oliver Hartkopp wrote:
>> Hello Vincent,
>>
>> On 24.09.25 14:40, syzbot ci wrote:
>>> syzbot ci has tested the following series
>>>
>>> [v1] pull-request: can-next 2025-09-24
>>> https://lore.kernel.org/all/20250924082104.595459-1-mkl@pengutronix.de
>>> * [PATCH net-next 01/48] can: m_can: use us_to_ktime() where appropriate
>>> * [PATCH net-next 02/48] MAINTAINERS: update Vincent Mailhol's email address
>>> * [PATCH net-next 03/48] can: dev: sort includes by alphabetical order
>>> * [PATCH net-next 04/48] can: peak: Modification of references to email
>>> accounts being deleted
>>> * [PATCH net-next 05/48] can: rcar_canfd: Update bit rate constants for RZ/G3E
>>> and R-Car Gen4
>>> * [PATCH net-next 06/48] can: rcar_canfd: Update RCANFD_CFG_* macros
>>> * [PATCH net-next 07/48] can: rcar_canfd: Simplify nominal bit rate config
>>> * [PATCH net-next 08/48] can: rcar_canfd: Simplify data bit rate config
>>> * [PATCH net-next 09/48] can: rcar_can: Consistently use ndev for net_device
>>> pointers
>>> * [PATCH net-next 10/48] can: rcar_can: Add helper variable dev to
>>> rcar_can_probe()
>>> * [PATCH net-next 11/48] can: rcar_can: Convert to Runtime PM
>>> * [PATCH net-next 12/48] can: rcar_can: Convert to BIT()
>>> * [PATCH net-next 13/48] can: rcar_can: Convert to GENMASK()
>>> * [PATCH net-next 14/48] can: rcar_can: CTLR bitfield conversion
>>> * [PATCH net-next 15/48] can: rcar_can: TFCR bitfield conversion
>>> * [PATCH net-next 16/48] can: rcar_can: BCR bitfield conversion
>>> * [PATCH net-next 17/48] can: rcar_can: Mailbox bitfield conversion
>>> * [PATCH net-next 18/48] can: rcar_can: Do not print alloc_candev() failures
>>> * [PATCH net-next 19/48] can: rcar_can: Convert to %pe
>>> * [PATCH net-next 20/48] can: esd_usb: Rework display of error messages
>>> * [PATCH net-next 21/48] can: esd_usb: Avoid errors triggered from USB disconnect
>>> * [PATCH net-next 22/48] can: raw: reorder struct uniqframe's members to
>>> optimise packing
>>> * [PATCH net-next 23/48] can: raw: use bitfields to store flags in struct
>>> raw_sock
>>> * [PATCH net-next 24/48] can: raw: reorder struct raw_sock's members to
>>> optimise packing
>>> * [PATCH net-next 25/48] can: annotate mtu accesses with READ_ONCE()
>>> * [PATCH net-next 26/48] can: dev: turn can_set_static_ctrlmode() into a non-
>>> inline function
>>> * [PATCH net-next 27/48] can: populate the minimum and maximum MTU values
>>> * [PATCH net-next 28/48] can: enable CAN XL for virtual CAN devices by default
>>> * [PATCH net-next 29/48] can: dev: move struct data_bittiming_params to linux/
>>> can/bittiming.h
>>> * [PATCH net-next 30/48] can: dev: make can_get_relative_tdco() FD agnostic
>>> and move it to bittiming.h
>>> * [PATCH net-next 31/48] can: netlink: document which symbols are FD specific
>>> * [PATCH net-next 32/48] can: netlink: refactor can_validate_bittiming()
>>> * [PATCH net-next 33/48] can: netlink: add can_validate_tdc()
>>> * [PATCH net-next 34/48] can: netlink: add can_validate_databittiming()
>>> * [PATCH net-next 35/48] can: netlink: refactor CAN_CTRLMODE_TDC_{AUTO,MANUAL}
>>> flag reset logic
>>> * [PATCH net-next 36/48] can: netlink: remove useless check in
>>> can_tdc_changelink()
>>> * [PATCH net-next 37/48] can: netlink: make can_tdc_changelink() FD agnostic
>>> * [PATCH net-next 38/48] can: netlink: add can_dtb_changelink()
>>> * [PATCH net-next 39/48] can: netlink: add can_ctrlmode_changelink()
>>> * [PATCH net-next 40/48] can: netlink: make can_tdc_get_size() FD agnostic
>>> * [PATCH net-next 41/48] can: netlink: add can_data_bittiming_get_size()
>>> * [PATCH net-next 42/48] can: netlink: add can_bittiming_fill_info()
>>> * [PATCH net-next 43/48] can: netlink: add can_bittiming_const_fill_info()
>>> * [PATCH net-next 44/48] can: netlink: add can_bitrate_const_fill_info()
>>> * [PATCH net-next 45/48] can: netlink: make can_tdc_fill_info() FD agnostic
>>> * [PATCH net-next 46/48] can: calc_bittiming: make can_calc_tdco() FD agnostic
>>> * [PATCH net-next 47/48] can: dev: add can_get_ctrlmode_str()
>>> * [PATCH net-next 48/48] can: netlink: add userland error messages
>>>
>>> and found the following issue:
>>> KASAN: slab-out-of-bounds Read in can_setup
>>>
>>> Full report is available here:
>>> https://ci.syzbot.org/series/7feff13b-7247-438c-9d92-b8e9fda977c7
>>>
>>> ***
>>>
>>> KASAN: slab-out-of-bounds Read in can_setup
>>>
>>> tree: net-next
>>> URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/
>>> net-next.git
>>> base: 315f423be0d1ebe720d8fd4fa6bed68586b13d34
>>> arch: amd64
>>> compiler: Debian clang version 20.1.8 (+
>>> +20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
>>> config: https://ci.syzbot.org/builds/08331a39-4a31-4f96-a377-3125df2af883/
>>> config
>>> C repro: https://ci.syzbot.org/findings/46cae752-cb54-4ceb-87cb-
>>> bb9d2fdb1d79/c_repro
>>> syz repro: https://ci.syzbot.org/findings/46cae752-cb54-4ceb-87cb-
>>> bb9d2fdb1d79/syz_repro
>>>
>>> netlink: 24 bytes leftover after parsing attributes in process `syz.0.17'.
>>> ==================================================================
>>> BUG: KASAN: slab-out-of-bounds in can_set_default_mtu drivers/net/can/dev/
>>> dev.c:350 [inline]
>>> BUG: KASAN: slab-out-of-bounds in can_setup+0x209/0x280 drivers/net/can/dev/
>>> dev.c:279
>>> Read of size 4 at addr ffff888106a6ee74 by task syz.0.17/5999
>>>
>>> CPU: 1 UID: 0 PID: 5999 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
>>> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-
>>> debian-1.16.2-1 04/01/2014
>>> Call Trace:
>>> <TASK>
>>> dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
>>> print_address_description mm/kasan/report.c:378 [inline]
>>> print_report+0xca/0x240 mm/kasan/report.c:482
>>> kasan_report+0x118/0x150 mm/kasan/report.c:595
>>> can_set_default_mtu drivers/net/can/dev/dev.c:350 [inline]
>>
>> When can_set_default_mtu() is called from the netlink config context it is also
>> used for virtual CAN interfaces (which was created by syzbot here), where the
>> priv pointer is not valid.
>
> Ack. I am pretty sure that I tested it on the virtual interfaces, but I did not
> have KASAN activated. So I did not notice the problem.
>
>> Please use
>>
>> struct can_priv *priv = safe_candev_priv(dev);
>>
>> to detect virtual CAN interfaces too.
>
> Exactly! I am reaching the same conclusion.
>
> Right now, I am testing this patch:
>
> diff --git a/drivers/net/can/dev/dev.c b/drivers/net/can/dev/dev.c
> index e5a82aa77958..1a309ae4850d 100644
> --- a/drivers/net/can/dev/dev.c
> +++ b/drivers/net/can/dev/dev.c
> @@ -345,9 +345,9 @@ EXPORT_SYMBOL_GPL(free_candev);
>
> void can_set_default_mtu(struct net_device *dev)
> {
> - struct can_priv *priv = netdev_priv(dev);
> + struct can_priv *priv = safe_candev_priv(dev);
>
> - if (priv->ctrlmode & CAN_CTRLMODE_FD) {
> + if (priv && (priv->ctrlmode & CAN_CTRLMODE_FD)) {
> dev->mtu = CANFD_MTU;
> dev->min_mtu = CANFD_MTU;
> dev->max_mtu = CANFD_MTU;
>
> It is compiling rigth now. Another potential fix could also be:
>
> diff --git a/drivers/net/can/dev/dev.c b/drivers/net/can/dev/dev.c
> index e5a82aa77958..66c7a9eee7dd 100644
> --- a/drivers/net/can/dev/dev.c
> +++ b/drivers/net/can/dev/dev.c
> @@ -273,11 +273,12 @@ void can_setup(struct net_device *dev)
> {
> dev->type = ARPHRD_CAN;
> dev->hard_header_len = 0;
> + dev->mtu = CAN_MTU;
> + dev->min_mtu = CAN_MTU;
> + dev->max_mtu = CAN_MTU;
> dev->addr_len = 0;
> dev->tx_queue_len = 10;
>
> - can_set_default_mtu(dev);
> -
> /* New-style flags. */
> dev->flags = IFF_NOARP;
> dev->features = NETIF_F_HW_CSUM;
>
I tend to prefer this kind of fix.
This would make clear that can_set_default_mtu() is only triggered when
a new netlink configuration process on real(!) CAN interfaces is finalized.
Maybe this restriction should go into a comment describing
can_set_default_mtu() then.
Best regards,
Oliver
> @Marc, once I finish testing, can I just send you a diff patch and ask to squash
> it in:
>
> [PATCH net-next 27/48] can: populate the minimum and maximum MTU values
>
> ?
>
>
> Yours sincerely,
> Vincent Mailhol
>
>
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