phylink_ethtool_ksettings_get can be called while the interface may not
even be up, which should not be a problem. But there are drivers (e.g.
gianfar) which connect to the PHY in .ndo_open and disconnect in
.ndo_close. While odd, to my knowledge this is again not illegal and
there may be more that do the same. But PHYLINK for example has this
check in phylink_ethtool_ksettings_get:
if (pl->phydev) {
phy_ethtool_ksettings_get(pl->phydev, kset);
} else {
kset->base.port = pl->link_port;
}
So it will not populate kset->base.speed if there is no PHY connected.
The speed will be 0, by way of a previous memset. Not SPEED_UNKNOWN.
It is arguable whether that is legal or not. include/uapi/linux/ethtool.h
says:
All values 0 to INT_MAX are legal.
By that measure it may be. But it sure would make users of the
__ethtool_get_link_ksettings API need make more complicated checks
(against -1, against 0, 1, etc). So far the kernel community has been ok
with just checking for SPEED_UNKNOWN.
Take net/sched/sch_taprio.c for example. The check in
taprio_set_picos_per_byte is currently not robust enough and will
trigger this division by zero, due to PHYLINK not setting SPEED_UNKNOWN:
if (!__ethtool_get_link_ksettings(dev, &ecmd) &&
ecmd.base.speed != SPEED_UNKNOWN)
picos_per_byte = div64_s64(NSEC_PER_SEC * 1000LL * 8,
ecmd.base.speed * 1000 * 1000);
[ 27.109992] Division by zero in kernel.
[ 27.113842] CPU: 1 PID: 198 Comm: tc Not tainted
5.3.0-rc5-01246-gc4006b8c2637-dirty #212
[ 27.121974] Hardware name: Freescale LS1021A
[ 27.126234] [<c03132e0>] (unwind_backtrace) from [<c030d8b8>]
(show_stack+0x10/0x14)
[ 27.133938] [<c030d8b8>] (show_stack) from [<c10b21b0>]
(dump_stack+0xb0/0xc4)
[ 27.141124] [<c10b21b0>] (dump_stack) from [<c10af97c>] (Ldiv0_64+0x8/0x18)
[ 27.148052] [<c10af97c>] (Ldiv0_64) from [<c0700260>] (div64_u64+0xcc/0xf0)
[ 27.154978] [<c0700260>] (div64_u64) from [<c07002d0>] (div64_s64+0x4c/0x68)
[ 27.161993] [<c07002d0>] (div64_s64) from [<c0f3d890>]
(taprio_set_picos_per_byte+0xe8/0xf4)
[ 27.170388] [<c0f3d890>] (taprio_set_picos_per_byte) from [<c0f3f614>]
(taprio_change+0x668/0xcec)
[ 27.179302] [<c0f3f614>] (taprio_change) from [<c0f2bc24>]
(qdisc_create+0x1fc/0x4f4)
[ 27.187091] [<c0f2bc24>] (qdisc_create) from [<c0f2c0c8>]
(tc_modify_qdisc+0x1ac/0x6f8)
[ 27.195055] [<c0f2c0c8>] (tc_modify_qdisc) from [<c0ee9604>]
(rtnetlink_rcv_msg+0x268/0x2dc)
[ 27.203449] [<c0ee9604>] (rtnetlink_rcv_msg) from [<c0f4fef0>]
(netlink_rcv_skb+0xe0/0x114)
[ 27.211756] [<c0f4fef0>] (netlink_rcv_skb) from [<c0f4f6cc>]
(netlink_unicast+0x1b4/0x22c)
[ 27.219977] [<c0f4f6cc>] (netlink_unicast) from [<c0f4fa84>]
(netlink_sendmsg+0x284/0x340)
[ 27.228198] [<c0f4fa84>] (netlink_sendmsg) from [<c0eae5fc>]
(sock_sendmsg+0x14/0x24)
[ 27.235988] [<c0eae5fc>] (sock_sendmsg) from [<c0eaedf8>]
(___sys_sendmsg+0x214/0x228)
[ 27.243863] [<c0eaedf8>] (___sys_sendmsg) from [<c0eb015c>]
(__sys_sendmsg+0x50/0x8c)
[ 27.251652] [<c0eb015c>] (__sys_sendmsg) from [<c0301000>]
(ret_fast_syscall+0x0/0x54)
[ 27.259524] Exception stack(0xe8045fa8 to 0xe8045ff0)
[ 27.264546] 5fa0: b6f608c8 000000f8 00000003 bed7e2f0
00000000 00000000
[ 27.272681] 5fc0: b6f608c8 000000f8 004ce54c 00000128 5d3ce8c7 00000000
00000026 00505c9c
[ 27.280812] 5fe0: 00000070 bed7e298 004ddd64 b6dd1e64
Cc: Russell King <rmk+ker...@arm.linux.org.uk>
Fixes: 9525ae83959b ("phylink: add phylink infrastructure")
Signed-off-by: Vladimir Oltean <olte...@gmail.com>
---
drivers/net/phy/phylink.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index a45c5de96ab1..3522eaf3e80c 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -1112,6 +1112,7 @@ int phylink_ethtool_ksettings_get(struct phylink *pl,
if (pl->phydev) {
phy_ethtool_ksettings_get(pl->phydev, kset);
} else {
+ kset->base.speed = SPEED_UNKNOWN;
kset->base.port = pl->link_port;
}
--
2.17.1
