struct can_priv has a set of flags (can_priv::ctrlmode) which are
correlated with the other fields of the structure. In
can_changelink(), those flags are set first and copied to can_priv. If
the function has to return early, for example due to an out of range
value provided by the user, then the global configuration might become
incoherent.
Example: the user provides an out of range dbitrate (e.g. 20
Mbps). The command fails (-EINVAL), however the FD flag was already
set resulting in a configuration where FD is on but the databittiming
parameters are empty.
* Illustration of above example *
| $ ip link set can0 type can bitrate 500000 dbitrate 20000000 fd on
| RTNETLINK answers: Invalid argument
| $ ip --details link show can0
| 1: can0: <NOARP,ECHO> mtu 72 qdisc noop state DOWN mode DEFAULT group default qlen 10
| link/can promiscuity 0 minmtu 0 maxmtu 0
| can <FD> state STOPPED restart-ms 0
^^ FD flag is set without any of the databittiming parameters...
| bitrate 500000 sample-point 0.875
| tq 12 prop-seg 69 phase-seg1 70 phase-seg2 20 sjw 1
| ES582.1/ES584.1: tseg1 2..256 tseg2 2..128 sjw 1..128 brp 1..512 brp-inc 1
| ES582.1/ES584.1: dtseg1 2..32 dtseg2 1..16 dsjw 1..8 dbrp 1..32 dbrp-inc 1
| clock 80000000 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
To prevent this from happening, we do a local copy of can_priv, work
on it, an copy it at the very end of the function (i.e. only if all
previous checks succeeded).
Once this done, there is no more need to have a temporary variable for
a specific parameter. As such, the bittiming and data bittiming (bt
and dbt) are directly written to the temporary priv variable.
Finally, function can_calc_tdco() was retrieving can_priv from the
net_device and directly modifying it. We changed the prototype so that
it instead writes its changes into our temporary priv variable.
Signed-off-by: Vincent Mailhol <[email protected]>
---
Resending because I got no answers on:
https://lore.kernel.org/linux-can/[email protected]/T/#u
(I guess everyone bas busy with the upcoming merge window)
I am not sure whether or not this needs a "Fixes" tag. Just in case,
there it is:
Fixes: 9859ccd2c8be ("can: introduce the data bitrate configuration for CAN FD")
* Changelog *
v1 -> v2:
- Change the prototype of can_calc_tdco() so that the changes are
applied to the temporary priv instead of netdev_priv(dev).
---
drivers/net/can/dev/bittiming.c | 8 +--
drivers/net/can/dev/netlink.c | 88 +++++++++++++++++----------------
include/linux/can/bittiming.h | 7 ++-
3 files changed, 53 insertions(+), 50 deletions(-)
diff --git a/drivers/net/can/dev/bittiming.c b/drivers/net/can/dev/bittiming.c
index f49170eadd54..bddd93e2e439 100644
--- a/drivers/net/can/dev/bittiming.c
+++ b/drivers/net/can/dev/bittiming.c
@@ -175,13 +175,9 @@ int can_calc_bittiming(struct net_device *dev, struct can_bittiming *bt,
return 0;
}
-void can_calc_tdco(struct net_device *dev)
+void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
+ const struct can_bittiming *dbt)
{
- struct can_priv *priv = netdev_priv(dev);
- const struct can_bittiming *dbt = &priv->data_bittiming;
- struct can_tdc *tdc = &priv->tdc;
- const struct can_tdc_const *tdc_const = priv->tdc_const;
-
if (!tdc_const)
return;
diff --git a/drivers/net/can/dev/netlink.c b/drivers/net/can/dev/netlink.c
index 80425636049d..50dfed462711 100644
--- a/drivers/net/can/dev/netlink.c
+++ b/drivers/net/can/dev/netlink.c
@@ -58,14 +58,20 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
struct nlattr *data[],
struct netlink_ext_ack *extack)
{
- struct can_priv *priv = netdev_priv(dev);
+ /* Work on a local copy of priv to prevent inconsistent value
+ * in case of early return. net/core/rtnetlink.c has a global
+ * mutex so using a static declaration is race free
+ */
+ static struct can_priv priv;
int err;
/* We need synchronization with dev->stop() */
ASSERT_RTNL();
+ memcpy(&priv, netdev_priv(dev), sizeof(priv));
+
if (data[IFLA_CAN_BITTIMING]) {
- struct can_bittiming bt;
+ struct can_bittiming *bt = &priv.bittiming;
/* Do not allow changing bittiming while running */
if (dev->flags & IFF_UP)
@@ -76,28 +82,26 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
* directly via do_set_bitrate(). Bail out if neither
* is given.
*/
- if (!priv->bittiming_const && !priv->do_set_bittiming)
+ if (!priv.bittiming_const && !priv.do_set_bittiming)
return -EOPNOTSUPP;
- memcpy(&bt, nla_data(data[IFLA_CAN_BITTIMING]), sizeof(bt));
- err = can_get_bittiming(dev, &bt,
- priv->bittiming_const,
- priv->bitrate_const,
- priv->bitrate_const_cnt);
+ memcpy(bt, nla_data(data[IFLA_CAN_BITTIMING]), sizeof(*bt));
+ err = can_get_bittiming(dev, bt,
+ priv.bittiming_const,
+ priv.bitrate_const,
+ priv.bitrate_const_cnt);
if (err)
return err;
- if (priv->bitrate_max && bt.bitrate > priv->bitrate_max) {
+ if (priv.bitrate_max && bt->bitrate > priv.bitrate_max) {
netdev_err(dev, "arbitration bitrate surpasses transceiver capabilities of %d bps\n",
- priv->bitrate_max);
+ priv.bitrate_max);
return -EINVAL;
}
- memcpy(&priv->bittiming, &bt, sizeof(bt));
-
- if (priv->do_set_bittiming) {
+ if (priv.do_set_bittiming) {
/* Finally, set the bit-timing registers */
- err = priv->do_set_bittiming(dev);
+ err = priv.do_set_bittiming(dev);
if (err)
return err;
}
@@ -112,11 +116,11 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
if (dev->flags & IFF_UP)
return -EBUSY;
cm = nla_data(data[IFLA_CAN_CTRLMODE]);
- ctrlstatic = priv->ctrlmode_static;
+ ctrlstatic = priv.ctrlmode_static;
maskedflags = cm->flags & cm->mask;
/* check whether provided bits are allowed to be passed */
- if (maskedflags & ~(priv->ctrlmode_supported | ctrlstatic))
+ if (maskedflags & ~(priv.ctrlmode_supported | ctrlstatic))
return -EOPNOTSUPP;
/* do not check for static fd-non-iso if 'fd' is disabled */
@@ -128,16 +132,16 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
return -EOPNOTSUPP;
/* clear bits to be modified and copy the flag values */
- priv->ctrlmode &= ~cm->mask;
- priv->ctrlmode |= maskedflags;
+ priv.ctrlmode &= ~cm->mask;
+ priv.ctrlmode |= maskedflags;
/* CAN_CTRLMODE_FD can only be set when driver supports FD */
- if (priv->ctrlmode & CAN_CTRLMODE_FD) {
+ if (priv.ctrlmode & CAN_CTRLMODE_FD) {
dev->mtu = CANFD_MTU;
} else {
dev->mtu = CAN_MTU;
- memset(&priv->data_bittiming, 0,
- sizeof(priv->data_bittiming));
+ memset(&priv.data_bittiming, 0,
+ sizeof(priv.data_bittiming));
}
}
@@ -145,7 +149,7 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
/* Do not allow changing restart delay while running */
if (dev->flags & IFF_UP)
return -EBUSY;
- priv->restart_ms = nla_get_u32(data[IFLA_CAN_RESTART_MS]);
+ priv.restart_ms = nla_get_u32(data[IFLA_CAN_RESTART_MS]);
}
if (data[IFLA_CAN_RESTART]) {
@@ -158,7 +162,7 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
}
if (data[IFLA_CAN_DATA_BITTIMING]) {
- struct can_bittiming dbt;
+ struct can_bittiming *dbt = &priv.data_bittiming;
/* Do not allow changing bittiming while running */
if (dev->flags & IFF_UP)
@@ -169,31 +173,29 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
* directly via do_set_bitrate(). Bail out if neither
* is given.
*/
- if (!priv->data_bittiming_const && !priv->do_set_data_bittiming)
+ if (!priv.data_bittiming_const && !priv.do_set_data_bittiming)
return -EOPNOTSUPP;
- memcpy(&dbt, nla_data(data[IFLA_CAN_DATA_BITTIMING]),
- sizeof(dbt));
- err = can_get_bittiming(dev, &dbt,
- priv->data_bittiming_const,
- priv->data_bitrate_const,
- priv->data_bitrate_const_cnt);
+ memcpy(dbt, nla_data(data[IFLA_CAN_DATA_BITTIMING]),
+ sizeof(*dbt));
+ err = can_get_bittiming(dev, dbt,
+ priv.data_bittiming_const,
+ priv.data_bitrate_const,
+ priv.data_bitrate_const_cnt);
if (err)
return err;
- if (priv->bitrate_max && dbt.bitrate > priv->bitrate_max) {
+ if (priv.bitrate_max && dbt->bitrate > priv.bitrate_max) {
netdev_err(dev, "canfd data bitrate surpasses transceiver capabilities of %d bps\n",
- priv->bitrate_max);
+ priv.bitrate_max);
return -EINVAL;
}
- memcpy(&priv->data_bittiming, &dbt, sizeof(dbt));
-
- can_calc_tdco(dev);
+ can_calc_tdco(&priv.tdc, priv.tdc_const, &priv.data_bittiming);
- if (priv->do_set_data_bittiming) {
+ if (priv.do_set_data_bittiming) {
/* Finally, set the bit-timing registers */
- err = priv->do_set_data_bittiming(dev);
+ err = priv.do_set_data_bittiming(dev);
if (err)
return err;
}
@@ -201,28 +203,30 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
if (data[IFLA_CAN_TERMINATION]) {
const u16 termval = nla_get_u16(data[IFLA_CAN_TERMINATION]);
- const unsigned int num_term = priv->termination_const_cnt;
+ const unsigned int num_term = priv.termination_const_cnt;
unsigned int i;
- if (!priv->do_set_termination)
+ if (!priv.do_set_termination)
return -EOPNOTSUPP;
/* check whether given value is supported by the interface */
for (i = 0; i < num_term; i++) {
- if (termval == priv->termination_const[i])
+ if (termval == priv.termination_const[i])
break;
}
if (i >= num_term)
return -EINVAL;
/* Finally, set the termination value */
- err = priv->do_set_termination(dev, termval);
+ err = priv.do_set_termination(dev, termval);
if (err)
return err;
- priv->termination = termval;
+ priv.termination = termval;
}
+ memcpy(netdev_priv(dev), &priv, sizeof(priv));
+
return 0;
}
diff --git a/include/linux/can/bittiming.h b/include/linux/can/bittiming.h
index 9de6e9053e34..b3c1711ee0f0 100644
--- a/include/linux/can/bittiming.h
+++ b/include/linux/can/bittiming.h
@@ -87,7 +87,8 @@ struct can_tdc_const {
int can_calc_bittiming(struct net_device *dev, struct can_bittiming *bt,
const struct can_bittiming_const *btc);
-void can_calc_tdco(struct net_device *dev);
+void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
+ const struct can_bittiming *dbt);
#else /* !CONFIG_CAN_CALC_BITTIMING */
static inline int
can_calc_bittiming(struct net_device *dev, struct can_bittiming *bt,
@@ -97,7 +98,9 @@ can_calc_bittiming(struct net_device *dev, struct can_bittiming *bt,
return -EINVAL;
}
-static inline void can_calc_tdco(struct net_device *dev)
+static inline void
+can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
+ const struct can_bittiming *dbt)
{
}
#endif /* CONFIG_CAN_CALC_BITTIMING */
--
2.31.1
On 03.09.2021 16:17:04, Vincent Mailhol wrote:
> struct can_priv has a set of flags (can_priv::ctrlmode) which are
> correlated with the other fields of the structure. In
> can_changelink(), those flags are set first and copied to can_priv. If
> the function has to return early, for example due to an out of range
> value provided by the user, then the global configuration might become
> incoherent.
>
> Example: the user provides an out of range dbitrate (e.g. 20
> Mbps). The command fails (-EINVAL), however the FD flag was already
> set resulting in a configuration where FD is on but the databittiming
> parameters are empty.
>
> * Illustration of above example *
>
> | $ ip link set can0 type can bitrate 500000 dbitrate 20000000 fd on
> | RTNETLINK answers: Invalid argument
> | $ ip --details link show can0
> | 1: can0: <NOARP,ECHO> mtu 72 qdisc noop state DOWN mode DEFAULT group default qlen 10
> | link/can promiscuity 0 minmtu 0 maxmtu 0
> | can <FD> state STOPPED restart-ms 0
> ^^ FD flag is set without any of the databittiming parameters...
> | bitrate 500000 sample-point 0.875
> | tq 12 prop-seg 69 phase-seg1 70 phase-seg2 20 sjw 1
> | ES582.1/ES584.1: tseg1 2..256 tseg2 2..128 sjw 1..128 brp 1..512 brp-inc 1
> | ES582.1/ES584.1: dtseg1 2..32 dtseg2 1..16 dsjw 1..8 dbrp 1..32 dbrp-inc 1
> | clock 80000000 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
>
> To prevent this from happening, we do a local copy of can_priv, work
> on it, an copy it at the very end of the function (i.e. only if all
> previous checks succeeded).
I don't like the optimization of using a static priv. If it's too big to
be allocated on the stack, allocate it on the heap, i.e. using
kmemdup()/kfree().
> Once this done, there is no more need to have a temporary variable for
> a specific parameter. As such, the bittiming and data bittiming (bt
> and dbt) are directly written to the temporary priv variable.
>
> Finally, function can_calc_tdco() was retrieving can_priv from the
> net_device and directly modifying it. We changed the prototype so that
> it instead writes its changes into our temporary priv variable.
Is it possible to split this into a separate patch, so that the part
without the tdco can be backported more easily to older kernels not
having tdco? The patch fixing the tdco would be the 2nd patch...
> Signed-off-by: Vincent Mailhol <[email protected]>
> ---
> Resending because I got no answers on:
> https://lore.kernel.org/linux-can/[email protected]/T/#u
> (I guess everyone bas busy with the upcoming merge window)
Busy yes, but not with the merge window :)
> I am not sure whether or not this needs a "Fixes" tag. Just in case,
> there it is:
>
> Fixes: 9859ccd2c8be ("can: introduce the data bitrate configuration for CAN FD")
...if it's possible to split this patch into 2 parts, add individual
fixes tags to them.
regards,
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
Vertretung West/Dortmund | Phone: +49-231-2826-924 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
On Mon. 6 Sep 2021 at 17:18, Marc Kleine-Budde <[email protected]> wrote:
> On 03.09.2021 16:17:04, Vincent Mailhol wrote:
> > struct can_priv has a set of flags (can_priv::ctrlmode) which are
> > correlated with the other fields of the structure. In
> > can_changelink(), those flags are set first and copied to can_priv. If
> > the function has to return early, for example due to an out of range
> > value provided by the user, then the global configuration might become
> > incoherent.
> >
> > Example: the user provides an out of range dbitrate (e.g. 20
> > Mbps). The command fails (-EINVAL), however the FD flag was already
> > set resulting in a configuration where FD is on but the databittiming
> > parameters are empty.
> >
> > * Illustration of above example *
> >
> > | $ ip link set can0 type can bitrate 500000 dbitrate 20000000 fd on
> > | RTNETLINK answers: Invalid argument
> > | $ ip --details link show can0
> > | 1: can0: <NOARP,ECHO> mtu 72 qdisc noop state DOWN mode DEFAULT group default qlen 10
> > | link/can promiscuity 0 minmtu 0 maxmtu 0
> > | can <FD> state STOPPED restart-ms 0
> > ^^ FD flag is set without any of the databittiming parameters...
> > | bitrate 500000 sample-point 0.875
> > | tq 12 prop-seg 69 phase-seg1 70 phase-seg2 20 sjw 1
> > | ES582.1/ES584.1: tseg1 2..256 tseg2 2..128 sjw 1..128 brp 1..512 brp-inc 1
> > | ES582.1/ES584.1: dtseg1 2..32 dtseg2 1..16 dsjw 1..8 dbrp 1..32 dbrp-inc 1
> > | clock 80000000 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
> >
> > To prevent this from happening, we do a local copy of can_priv, work
> > on it, an copy it at the very end of the function (i.e. only if all
> > previous checks succeeded).
>
> I don't like the optimization of using a static priv. If it's too big to
> be allocated on the stack, allocate it on the heap, i.e. using
> kmemdup()/kfree().
The static declaration is only an issue of coding style, correct?
Or is there an actual risk of doing so?
This is for my understanding, I will remove the static
declaration regardless of your answer.
On my x86_64 machine, sizeof(priv) is 448 and if I declare priv on the stack:
| $ objdump -d drivers/net/can/dev/netlink.o | ./scripts/checkstack.pl
| 0x00000000000002100 can_changelink []: 1200
So I will allocate it on the heap.
N.B. In above figures CONFIG_CAN_LEDS is *off* because that driver
was tagged as broken in:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=30f3b42147ba6f29bc95c1bba34468740762d91b
> > Once this done, there is no more need to have a temporary variable for
> > a specific parameter. As such, the bittiming and data bittiming (bt
> > and dbt) are directly written to the temporary priv variable.
> >
> > Finally, function can_calc_tdco() was retrieving can_priv from the
> > net_device and directly modifying it. We changed the prototype so that
> > it instead writes its changes into our temporary priv variable.
>
> Is it possible to split this into a separate patch, so that the part
> without the tdco can be backported more easily to older kernels not
> having tdco? The patch fixing the tdco would be the 2nd patch...
ACK. I will send a v3 with that split.
> > Signed-off-by: Vincent Mailhol <[email protected]>
> > ---
> > Resending because I got no answers on:
> > https://lore.kernel.org/linux-can/[email protected]/T/#u
> > (I guess everyone bas busy with the upcoming merge window)
>
> Busy yes, but not with the merge window :)
>
> > I am not sure whether or not this needs a "Fixes" tag. Just in case,
> > there it is:
> >
> > Fixes: 9859ccd2c8be ("can: introduce the data bitrate configuration for CAN FD")
>
> ...if it's possible to split this patch into 2 parts, add individual
> fixes tags to them.
ACK.
> regards,
> Marc
>
> --
> Pengutronix e.K. | Marc Kleine-Budde |
> Embedded Linux | https://www.pengutronix.de |
> Vertretung West/Dortmund | Phone: +49-231-2826-924 |
> Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
On 06.09.2021 23:17:40, Vincent MAILHOL wrote:
> > > To prevent this from happening, we do a local copy of can_priv, work
> > > on it, an copy it at the very end of the function (i.e. only if all
> > > previous checks succeeded).
> >
> > I don't like the optimization of using a static priv. If it's too big to
> > be allocated on the stack, allocate it on the heap, i.e. using
> > kmemdup()/kfree().
>
> The static declaration is only an issue of coding style, correct?
I don't know (but I haven't checked) if the coding style doc says
anything about that.
> Or is there an actual risk of doing so?
As you pointed out, this relies on the serialization of the changelink
callback by the networking stack. There's no sane way in C to track this
requirement in the networking stack, so I don't want to have any
roadblocks and/or potential bugs in the CAN code. Marking a variable as
static places it in the BSS section, right? This mean, the memory is
always "used", even if not setting the bitrate.
> This is for my understanding, I will remove the static
> declaration regardless of your answer.
tnx
> On my x86_64 machine, sizeof(priv) is 448 and if I declare priv on the stack:
> | $ objdump -d drivers/net/can/dev/netlink.o | ./scripts/checkstack.pl
> | 0x00000000000002100 can_changelink []: 1200
>
> So I will allocate it on the heap.
Sounds reasonable.
> N.B. In above figures CONFIG_CAN_LEDS is *off* because that driver
> was tagged as broken in:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=30f3b42147ba6f29bc95c1bba34468740762d91b
ok - BTW: I think we can remove LEDs support now, it's marked as broken
for more than 3 years.
> > > Once this done, there is no more need to have a temporary variable for
> > > a specific parameter. As such, the bittiming and data bittiming (bt
> > > and dbt) are directly written to the temporary priv variable.
> > >
> > > Finally, function can_calc_tdco() was retrieving can_priv from the
> > > net_device and directly modifying it. We changed the prototype so that
> > > it instead writes its changes into our temporary priv variable.
> >
> > Is it possible to split this into a separate patch, so that the part
> > without the tdco can be backported more easily to older kernels not
> > having tdco? The patch fixing the tdco would be the 2nd patch...
>
> ACK. I will send a v3 with that split.
Thanks for helping taking care of the LTS kernels!
regards,
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
Vertretung West/Dortmund | Phone: +49-231-2826-924 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |