ethtool: Remove link_mode param and derive link params from driver

Some drivers clear the 'ethtool_link_ksettings' struct in their
get_link_ksettings() callback, before populating it with actual values.
Such drivers will set the new 'link_mode' field to zero, resulting in
user space receiving wrong link mode information given that zero is a
valid value for the field.

Another problem is that some drivers (notably tun) can report random
values in the 'link_mode' field. This can result in a general protection
fault when the field is used as an index to the 'link_mode_params' array
[1].

This happens because such drivers implement their set_link_ksettings()
callback by simply overwriting their private copy of
'ethtool_link_ksettings' struct with the one they get from the stack,
which is not always properly initialized.

Fix these problems by removing 'link_mode' from 'ethtool_link_ksettings'
and instead have drivers call ethtool_params_from_link_mode() with the
current link mode. The function will derive the link parameters (e.g.,
speed) from the link mode and fill them in the 'ethtool_link_ksettings'
struct.

v3:
	* Remove link_mode parameter and derive the link parameters in
	  the driver instead of passing link_mode parameter to ethtool
	  and derive it there.

v2:
	* Introduce 'cap_link_mode_supported' instead of adding a
	  validity field to 'ethtool_link_ksettings' struct.

[1]
general protection fault, probably for non-canonical address 0xdffffc00f14cc32c: 0000 [#1] PREEMPT SMP KASAN
KASAN: probably user-memory-access in range [0x000000078a661960-0x000000078a661967]
CPU: 0 PID: 8452 Comm: syz-executor360 Not tainted 5.11.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__ethtool_get_link_ksettings+0x1a3/0x3a0 net/ethtool/ioctl.c:446
Code: b7 3e fa 83 fd ff 0f 84 30 01 00 00 e8 16 b0 3e fa 48 8d 3c ed 60 d5 69 8a 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 14 02 48 89 f8 83 e0 07 83 c0 03
+38 d0 7c 08 84 d2 0f 85 b9
RSP: 0018:ffffc900019df7a0 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffff888026136008 RCX: 0000000000000000
RDX: 00000000f14cc32c RSI: ffffffff873439ca RDI: 000000078a661960
RBP: 00000000ffff8880 R08: 00000000ffffffff R09: ffff88802613606f
R10: ffffffff873439bc R11: 0000000000000000 R12: 0000000000000000
R13: ffff88802613606c R14: ffff888011d0c210 R15: ffff888011d0c210
FS:  0000000000749300(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004b60f0 CR3: 00000000185c2000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 linkinfo_prepare_data+0xfd/0x280 net/ethtool/linkinfo.c:37
 ethnl_default_notify+0x1dc/0x630 net/ethtool/netlink.c:586
 ethtool_notify+0xbd/0x1f0 net/ethtool/netlink.c:656
 ethtool_set_link_ksettings+0x277/0x330 net/ethtool/ioctl.c:620
 dev_ethtool+0x2b35/0x45d0 net/ethtool/ioctl.c:2842
 dev_ioctl+0x463/0xb70 net/core/dev_ioctl.c:440
 sock_do_ioctl+0x148/0x2d0 net/socket.c:1060
 sock_ioctl+0x477/0x6a0 net/socket.c:1177
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl fs/ioctl.c:739 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: c890704 ("ethtool: Get link mode in use instead of speed and duplex parameters")
Signed-off-by: Danielle Ratson <danieller@nvidia.com>
Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_ethtool.c

@@ -1230,16 +1230,22 @@ mlxsw_sp1_from_ptys_link_mode(struct mlxsw_sp *mlxsw_sp, bool carrier_ok,
 			      u32 ptys_eth_proto,
 			      struct ethtool_link_ksettings *cmd)
 {
+	struct mlxsw_sp1_port_link_mode link;
 	int i;
 
-	cmd->link_mode = -1;
+	cmd->base.speed = SPEED_UNKNOWN;
+	cmd->base.duplex = DUPLEX_UNKNOWN;
+	cmd->lanes = 0;
 
 	if (!carrier_ok)
 		return;
 
 	for (i = 0; i < MLXSW_SP1_PORT_LINK_MODE_LEN; i++) {
-		if (ptys_eth_proto & mlxsw_sp1_port_link_mode[i].mask)
-			cmd->link_mode = mlxsw_sp1_port_link_mode[i].mask_ethtool;
+		if (ptys_eth_proto & mlxsw_sp1_port_link_mode[i].mask) {
+			link = mlxsw_sp1_port_link_mode[i];
+			ethtool_params_from_link_mode(cmd,
+						      link.mask_ethtool);
+		}
 	}
 }
 
@@ -1672,15 +1678,18 @@ mlxsw_sp2_from_ptys_link_mode(struct mlxsw_sp *mlxsw_sp, bool carrier_ok,
 	struct mlxsw_sp2_port_link_mode link;
 	int i;
 
-	cmd->link_mode = -1;
+	cmd->base.speed = SPEED_UNKNOWN;
+	cmd->base.duplex = DUPLEX_UNKNOWN;
+	cmd->lanes = 0;
 
 	if (!carrier_ok)
 		return;
 
 	for (i = 0; i < MLXSW_SP2_PORT_LINK_MODE_LEN; i++) {
 		if (ptys_eth_proto & mlxsw_sp2_port_link_mode[i].mask) {
 			link = mlxsw_sp2_port_link_mode[i];
-			cmd->link_mode = link.mask_ethtool[1];
+			ethtool_params_from_link_mode(cmd,
+						      link.mask_ethtool[1]);
 		}
 	}
 }

include/linux/ethtool.h

@@ -127,7 +127,6 @@ struct ethtool_link_ksettings {
 		__ETHTOOL_DECLARE_LINK_MODE_MASK(lp_advertising);
 	} link_modes;
 	u32	lanes;
-	enum ethtool_link_mode_bit_indices link_mode;
 };
 
 /**
@@ -574,4 +573,12 @@ struct ethtool_phy_ops {
  */
 void ethtool_set_ethtool_phy_ops(const struct ethtool_phy_ops *ops);
 
+/*
+ * ethtool_params_from_link_mode - Derive link parameters from a given link mode
+ * @link_ksettings: Link parameters to be derived from the link mode
+ * @link_mode: Link mode
+ */
+void
+ethtool_params_from_link_mode(struct ethtool_link_ksettings *link_ksettings,
+			      enum ethtool_link_mode_bit_indices link_mode);
 #endif /* _LINUX_ETHTOOL_H */

net/ethtool/common.c

@@ -562,3 +562,19 @@ void ethtool_set_ethtool_phy_ops(const struct ethtool_phy_ops *ops)
 	rtnl_unlock();
 }
 EXPORT_SYMBOL_GPL(ethtool_set_ethtool_phy_ops);
+
+void
+ethtool_params_from_link_mode(struct ethtool_link_ksettings *link_ksettings,
+			      enum ethtool_link_mode_bit_indices link_mode)
+{
+	const struct link_mode_info *link_info;
+
+	if (WARN_ON_ONCE(link_mode >= __ETHTOOL_LINK_MODE_MASK_NBITS))
+		return;
+
+	link_info = &link_mode_params[link_mode];
+	link_ksettings->base.speed = link_info->speed;
+	link_ksettings->lanes = link_info->lanes;
+	link_ksettings->base.duplex = link_info->duplex;
+}
+EXPORT_SYMBOL_GPL(ethtool_params_from_link_mode);

net/ethtool/ioctl.c

@@ -426,29 +426,13 @@ struct ethtool_link_usettings {
 int __ethtool_get_link_ksettings(struct net_device *dev,
 				 struct ethtool_link_ksettings *link_ksettings)
 {
-	const struct link_mode_info *link_info;
-	int err;
-
 	ASSERT_RTNL();
 
 	if (!dev->ethtool_ops->get_link_ksettings)
 		return -EOPNOTSUPP;
 
 	memset(link_ksettings, 0, sizeof(*link_ksettings));
-
-	link_ksettings->link_mode = -1;
-	err = dev->ethtool_ops->get_link_ksettings(dev, link_ksettings);
-	if (err)
-		return err;
-
-	if (link_ksettings->link_mode != -1) {
-		link_info = &link_mode_params[link_ksettings->link_mode];
-		link_ksettings->base.speed = link_info->speed;
-		link_ksettings->lanes = link_info->lanes;
-		link_ksettings->base.duplex = link_info->duplex;
-	}
-
-	return 0;
+	return dev->ethtool_ops->get_link_ksettings(dev, link_ksettings);
 }
 EXPORT_SYMBOL(__ethtool_get_link_ksettings);