On Tue. 7 Sep 2021 at 01:03, Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> 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 <mailhol.vincent@xxxxxxxxxx> > --- > 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