[PATCH v3 1/2] can: netlink: prevent incoherent can configuration in case of early return
From: Vincent Mailhol <hidden>
Date: 2021-09-06 16:03:53
Also in:
lkml, netdev
Subsystem:
can network drivers, the rest · Maintainers:
Marc Kleine-Budde, Vincent Mailhol, Linus Torvalds
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 <redacted>
---
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