This series of two patch prevents, once for all, can_priv to be in an
inconsistent state in case of an early return in can_changelink() due
to invalid parameters.
* Changelog *
v2 -> v3:
- Allocate the temporary struct can_priv on the heap instead of
declaring it as static.
- Split the patch into two to make it easier to backport to LTS
kernels and add the "Fixes" tag.
v1 -> v2:
- Change the prototype of can_calc_tdco() so that the changes are
applied to the temporary priv instead of netdev_priv(dev).
Vincent Mailhol (2):
can: netlink: prevent incoherent can configuration in case of early
return
can: bittiming: change can_calc_tdco()'s prototype to not directly
modify priv
drivers/net/can/dev/bittiming.c | 8 ++------
drivers/net/can/dev/netlink.c | 34 ++++++++++++++++++---------------
include/linux/can/bittiming.h | 7 +++++--
3 files changed, 26 insertions(+), 23 deletions(-)
--
2.32.0
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.
N.B. The temporary can_priv is too big to be allocated on the stack
because, on x86_64 sizeof(struct can_priv) is 448 and:
| $ objdump -d drivers/net/can/dev/netlink.o | ./scripts/checkstack.pl
| 0x00000000000002100 can_changelink []: 1200
Fixes: 9859ccd2c8be ("can: introduce the data bitrate configuration for CAN FD")
Signed-off-by: Vincent Mailhol <[email protected]>
---
drivers/net/can/dev/netlink.c | 32 ++++++++++++++++++--------------
1 file changed, 18 insertions(+), 14 deletions(-)
diff --git a/drivers/net/can/dev/netlink.c b/drivers/net/can/dev/netlink.c
index 80425636049d..21b76ca8cb22 100644
--- a/drivers/net/can/dev/netlink.c
+++ b/drivers/net/can/dev/netlink.c
@@ -58,14 +58,19 @@ 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.
+ */
+ static struct can_priv *priv;
int err;
/* We need synchronization with dev->stop() */
ASSERT_RTNL();
+ priv = kmemdup(netdev_priv(dev), sizeof(*priv), GFP_KERNEL);
+
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)
@@ -79,22 +84,20 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
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,
+ 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);
return -EINVAL;
}
- memcpy(&priv->bittiming, &bt, sizeof(bt));
-
if (priv->do_set_bittiming) {
/* Finally, set the bit-timing registers */
err = priv->do_set_bittiming(dev);
@@ -158,7 +161,7 @@ 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)
@@ -172,23 +175,21 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
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,
+ 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);
return -EINVAL;
}
- memcpy(&priv->data_bittiming, &dbt, sizeof(dbt));
-
can_calc_tdco(dev);
if (priv->do_set_data_bittiming) {
@@ -223,6 +224,9 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
priv->termination = termval;
}
+ memcpy(netdev_priv(dev), priv, sizeof(*priv));
+ kfree(priv);
+
return 0;
}
--
2.32.0
In previous commit, we introduced a temporary priv variable in
can_changelink(), wrote the changes to it and committed all changes at
the very end of the function.
However, the function can_calc_tdco() directly retrieves can_priv from
the net_device and directly modifies it. We change the prototype so
that it instead writes its changes to a struct can_priv that is passed
as an argument. This way, can_changelink() can pass the newly
introduced temporary priv variable.
Fixes: c25cc7993243 ("can: bittiming: add calculation for CAN FD Transmitter Delay Compensation (TDC)")
Signed-off-by: Vincent Mailhol <[email protected]>
---
drivers/net/can/dev/bittiming.c | 8 ++------
drivers/net/can/dev/netlink.c | 2 +-
include/linux/can/bittiming.h | 7 +++++--
3 files changed, 8 insertions(+), 9 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 21b76ca8cb22..66815ea6046e 100644
--- a/drivers/net/can/dev/netlink.c
+++ b/drivers/net/can/dev/netlink.c
@@ -190,7 +190,7 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
return -EINVAL;
}
- can_calc_tdco(dev);
+ can_calc_tdco(&priv->tdc, priv->tdc_const, &priv->data_bittiming);
if (priv->do_set_data_bittiming) {
/* Finally, set the bit-timing registers */
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 */
--
2.32.0
On Tue. 7 Sep 2021 at 01:03, Vincent Mailhol <[email protected]> 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).
>
> 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.
>
>
> N.B. The temporary can_priv is too big to be allocated on the stack
> because, on x86_64 sizeof(struct can_priv) is 448 and:
>
> | $ objdump -d drivers/net/can/dev/netlink.o | ./scripts/checkstack.pl
> | 0x00000000000002100 can_changelink []: 1200
>
>
> Fixes: 9859ccd2c8be ("can: introduce the data bitrate configuration for CAN FD")
> Signed-off-by: Vincent Mailhol <[email protected]>
> ---
> drivers/net/can/dev/netlink.c | 32 ++++++++++++++++++--------------
> 1 file changed, 18 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/net/can/dev/netlink.c b/drivers/net/can/dev/netlink.c
> index 80425636049d..21b76ca8cb22 100644
> --- a/drivers/net/can/dev/netlink.c
> +++ b/drivers/net/can/dev/netlink.c
> @@ -58,14 +58,19 @@ 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.
> + */
> + static struct can_priv *priv;
> int err;
>
> /* We need synchronization with dev->stop() */
> ASSERT_RTNL();
>
> + priv = kmemdup(netdev_priv(dev), sizeof(*priv), GFP_KERNEL);
Arg... I forgot to check the return value.
+ if (!priv)
+ return -ENOMEM;
I will send a v4, sorry for the noise.
Yours sincerely,
Vincent
On Tue. 7 Sep. 2021 at 01:03, Vincent Mailhol
<[email protected]> 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).
>
> 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.
>
>
> N.B. The temporary can_priv is too big to be allocated on the stack
> because, on x86_64 sizeof(struct can_priv) is 448 and:
>
> | $ objdump -d drivers/net/can/dev/netlink.o | ./scripts/checkstack.pl
> | 0x00000000000002100 can_changelink []: 1200
>
>
> Fixes: 9859ccd2c8be ("can: introduce the data bitrate configuration for CAN FD")
> Signed-off-by: Vincent Mailhol <[email protected]>
> ---
> drivers/net/can/dev/netlink.c | 32 ++++++++++++++++++--------------
> 1 file changed, 18 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/net/can/dev/netlink.c b/drivers/net/can/dev/netlink.c
> index 80425636049d..21b76ca8cb22 100644
> --- a/drivers/net/can/dev/netlink.c
> +++ b/drivers/net/can/dev/netlink.c
> @@ -58,14 +58,19 @@ 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.
> + */
> + static struct can_priv *priv;
> int err;
>
> /* We need synchronization with dev->stop() */
> ASSERT_RTNL();
>
> + priv = kmemdup(netdev_priv(dev), sizeof(*priv), GFP_KERNEL);
> +
> 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)
> @@ -79,22 +84,20 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
> 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,
> + 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);
> return -EINVAL;
> }
>
> - memcpy(&priv->bittiming, &bt, sizeof(bt));
> -
> if (priv->do_set_bittiming) {
> /* Finally, set the bit-timing registers */
> err = priv->do_set_bittiming(dev);
Actually, there is a big issue with my approach: the
do_set_bittiming() and some other callback functions need to
access priv. However, the changes being in the temporary
variable, these will not be visible by the device.
I will rework all that a little bit more before sending v4.
Yours sincerely,
Vincent Mailhol