I have a small, embedded, completely self cross-compiled installation on a mips SoC.
SoC is based on a Mediatek MT7628 sporting a Wifi interface (2.4MHz only), a 100Mbps Ethernet MAC and an internal 5port Ethernet switch (one of the ports is connected to MAC).
I compiled Ethernet device driver (mtk-eth.ko) as installable module.
If I boot without the module (I actually renamed it so udevd doesn't manage to install it "automatically") I don't have an Ethernet device, exactly as expected:
# ip a1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue qlen 1000 link/ether b8:d8:12:64:b9:a0 brd ff:ff:ff:ff:ff:ff inet 192.168.7.130/24 brd 192.168.7.255 scope global noprefixroute wlan0 valid_lft forever preferred_lft foreverSo far nothing strange.Next I manually install the module:
# modprobe mtk-eth[ 6591.429607] mtk_soc_eth 10100000.ethernet: generated random MAC address 0a:90:77:c7:1d:f3[ 6591.461683] mtk_soc_eth 10100000.ethernet eth0: mediatek frame engine at 0xb0100000, irq 5[ 6591.659810] libphy: dsa slave smi: probed[ 6591.674778] mt7628-esw 10110000.esw: nonfatal error -122 setting MTU on port 0[ 6591.693746] mt7628-esw 10110000.esw lan (uninitialized): PHY [dsa-0.0:00] driver [Generic PHY] (irq=POLL)[ 6591.728356] mt7628-esw 10110000.esw: configuring for fixed/mii link mode[ 6591.736381] DSA: tree 0 setup[ 6591.751095] mt7628-esw 10110000.esw: Link is Up - 100Mbps/Full - flow control off[ 6595.094324] mt7628-esw 10110000.esw: port 0 link changed 0x1# ip a1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue qlen 1000 link/ether b8:d8:12:64:b9:a0 brd ff:ff:ff:ff:ff:ff inet 192.168.7.130/24 brd 192.168.7.255 scope global noprefixroute wlan0 valid_lft forever preferred_lft forever4: eth0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop qlen 1000 link/ether 0a:90:77:c7:1d:f3 brd ff:ff:ff:ff:ff:ff5: lan@eth0: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop qlen 1000 link/ether 0a:90:77:c7:1d:f3 brd ff:ff:ff:ff:ff:ffThis gives me two devices: the expected eth0, an unexpected lan@eth0 but still no connection. This is right because I have no DHCP client running (WiFi is handled separately by IWD).
Starting the DHCP client gives me connection:
# dhcpcd -b eth0dhcpcd-9.4.0 startingsandbox unavailable: seccompDUID 00:01:00:01:c7:92:bc:8f:b8:d8:12:64:b9:a2dhcp_vendor: No such processsandbox unavailable: seccompforked to background, child pid 850[ 6671.439622] mtk_soc_eth 10100000.ethernet eth0: configuring for fixed/mii link mode[ 6671.447753] mtk_soc_eth 10100000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx# ip a1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue qlen 1000 link/ether b8:d8:12:64:b9:a0 brd ff:ff:ff:ff:ff:ff inet 192.168.7.130/24 brd 192.168.7.255 scope global noprefixroute wlan0 valid_lft forever preferred_lft forever5: lan@if4: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop qlen 1000 link/ether 0a:90:77:c7:1d:f3 brd ff:ff:ff:ff:ff:ff6: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000 link/ether 9a:cf:60:d9:2e:a1 brd ff:ff:ff:ff:ff:ff inet 192.168.7.106/24 brd 192.168.7.255 scope global dynamic noprefixroute eth0 valid_lft 43191sec preferred_lft 37791secNotice only "standard" eth0 actually gets an IP address and "auxiliary" interface changed name lan@eth0 -> lan@if4.
What is this second "device"?What is its purpose and how am I supposed to use it (IFF I'm supposed to use it).Notice also bringing down eth0 actually seems to act on "auxiliary" device:
# ip l set eth0 down[ 8558.176702] mtk_soc_eth 10100000.ethernet eth0: Link is Down# ip a1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue qlen 1000 link/ether b8:d8:12:64:b9:a0 brd ff:ff:ff:ff:ff:ff inet 192.168.7.130/24 brd 192.168.7.255 scope global noprefixroute wlan0 valid_lft forever preferred_lft forever5: lan@if4: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop qlen 1000 link/ether 0a:90:77:c7:1d:f3 brd ff:ff:ff:ff:ff:ff6: eth0: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast qlen 1000Attempt to remove the mtk-eth module results in Kernel error:
# rmmod mtk-eth[ 6634.791361] ------------[ cut here ]------------[ 6634.796077] WARNING: CPU: 0 PID: 841 at drivers/net/phy/phylink.c:1151 0x80302674[ 6634.809938] RTNL: assertion failed at drivers/net/phy/phylink.c (1151)[ 6634.819931] Modules linked in: mtk_eth(-) des_generic libdes cbc ecb algif_skcipher hmac sha512_generic sha1_generic md5 md4 algif_hash af_alg mt7603e mt76 mac80211 sha256_generic libsha256 ehci_platform ohci_platform ohci_hcd ehci_hcd cfg80211 rfkill usbcore libarc4 usb_common[ 6634.848585] CPU: 0 PID: 841 Comm: rmmod Not tainted 5.8.0 #2[ 6634.857694] Stack : 80450000 80410e8c 804493fc 864d1d24 00000000 00000000 00000000 00000000[ 6634.869806] 00000000 00000000 00000000 00000000 00000000 00000001 864d1cd0 80490000[ 6634.881851] 864d1d68 00000000 00000000 ffff00fe 00000038 8025e724 00000006 876d5e58[ 6634.890364] 7fca7028 7fca706c 7fca7070 7fca7074 8041e310 80490000 80000000 00000009[ 6634.905154] 80467cc0 7fc3e284 00420000 004f0950 80495220 32cc152e 08072098 80500000[ 6634.917055] ...[ 6634.919556] Call Trace:[ 6634.919579] [<8025e724>] 0x8025e724[ 6634.931103] [<8000abf4>] 0x8000abf4[ 6634.934661] [<8000abfc>] 0x8000abfc[ 6634.938196] [<8001d990>] 0x8001d990[ 6634.955157] [<80302674>] 0x80302674[ 6634.958716] [<80302674>] 0x80302674[ 6634.968796] [<80302674>] 0x80302674[ 6634.975843] [<8001da04>] 0x8001da04[ 6634.979408] [<80302674>] 0x80302674[ 6634.989141] [<80158110>] 0x80158110[ 6634.996066] [<c00b10c4>] 0xc00b10c4[ 6634.999625] [<c00b12c4>] 0xc00b12c4[ 6635.009387] [<802c9c5c>] 0x802c9c5c[ 6635.016419] [<802c991c>] 0x802c991c[ 6635.019974] [<802c9dc0>] 0x802c9dc0[ 6635.029705] [<802c86e0>] 0x802c86e0[ 6635.036620] [<8007849c>] 0x8007849c[ 6635.040176] [<800bc5a4>] 0x800bc5a4[ 6635.049933] [<8002ec50>] 0x8002ec50[ 6635.056920] [<8000f14c>] 0x8000f14c[ 6635.060492] [ 6635.068472] ---[ end trace a60217f8a7ca79c8 ]---[ 6635.076697] ------------[ cut here ]------------[ 6635.084835] WARNING: CPU: 0 PID: 841 at drivers/net/phy/phylink.c:1030 0x80301a4c[ 6635.095828] RTNL: assertion failed at drivers/net/phy/phylink.c (1030)[ 6635.105831] Modules linked in: mtk_eth(-) des_generic libdes cbc ecb algif_skcipher hmac sha512_generic sha1_generic md5 md4 algif_hash af_alg mt7603e mt76 mac80211 sha256_generic libsha256 ehci_platform ohci_platform ohci_hcd ehci_hcd cfg80211 rfkill usbcore libarc4 usb_common[ 6635.134359] CPU: 0 PID: 841 Comm: rmmod Tainted: G W 5.8.0 #2[ 6635.145331] Stack : 80450000 80410e80 804493fc 864d1d14 00000000 00000000 00000000 00000000[ 6635.157222] 00000000 00000000 00000000 00000000 00000000 00000001 864d1cc0 80490000[ 6635.169427] 864d1d58 00000000 00000000 ffff00fe 00000038 8025e724 00000006 876d5e58[ 6635.181471] 7fca7028 7fca706c 7fca7070 7fca7074 8041e310 80490000 80000000 00000009[ 6635.190097] 80467cc0 0000007c 00420000 004f0950 80495220 32cc152e 08072098 80500000[ 6635.204965] ...[ 6635.207470] Call Trace:[ 6635.207493] [<8025e724>] 0x8025e724[ 6635.221955] [<8000abf4>] 0x8000abf4[ 6635.225509] [<8000abfc>] 0x8000abfc[ 6635.229045] [<8001d990>] 0x8001d990[ 6635.241166] [<80301a4c>] 0x80301a4c[ 6635.244725] [<80301a4c>] 0x80301a4c[ 6635.248258] [<80301a4c>] 0x80301a4c[ 6635.262154] [<8001da04>] 0x8001da04[ 6635.265718] [<c00af0c0>] 0xc00af0c0[ 6635.269251] [<80406134>] 0x80406134[ 6635.282048] [<80301a4c>] 0x80301a4c[ 6635.285608] [<80302690>] 0x80302690[ 6635.289142] [<80158110>] 0x80158110[ 6635.301514] [<c00b1120>] 0xc00b1120[ 6635.305074] [<c00b12c4>] 0xc00b12c4[ 6635.308611] [<802c9c5c>] 0x802c9c5c[ 6635.321116] [<802c991c>] 0x802c991c[ 6635.324673] [<802c9dc0>] 0x802c9dc0[ 6635.328209] [<802c86e0>] 0x802c86e0[ 6635.341418] [<8007849c>] 0x8007849c[ 6635.344976] [<800bc5a4>] 0x800bc5a4[ 6635.348511] [<8002ec50>] 0x8002ec50[ 6635.361159] [<8000f14c>] 0x8000f14c[ 6635.364729] [ 6635.366243] ---[ end trace a60217f8a7ca79c9 ]---[ 6635.380166] ------------[ cut here ]------------[ 6635.385575] WARNING: CPU: 0 PID: 841 at lib/refcount.c:28 0xc00b1258[ 6635.397959] refcount_t: underflow; use-after-free.[ 6635.406183] Modules linked in: mtk_eth(-) des_generic libdes cbc ecb algif_skcipher hmac sha512_generic sha1_generic md5 md4 algif_hash af_alg mt7603e mt76 mac80211 sha256_generic libsha256 ehci_platform ohci_platform ohci_hcd ehci_hcd cfg80211 rfkill usbcore libarc4 usb_common[ 6635.434814] CPU: 0 PID: 841 Comm: rmmod Tainted: G W 5.8.0 #2[ 6635.445430] Stack : 80450000 80410e80 804493fc 864d1d44 00000000 00000000 00000000 00000000[ 6635.457327] 00000000 00000000 00000000 00000000 00000000 00000001 864d1cf0 80490000[ 6635.469233] 864d1d88 00000000 00000000 ffff00fe 00000038 8025e724 00000006 876d5e58[ 6635.481410] 7fca7028 7fca706c 7fca7070 7fca7074 8041e310 80490000 80000000 00000009[ 6635.489923] 8043f744 0000007c 00420000 004f0950 80495220 32cc152e 08072098 80500000[ 6635.504762] ...[ 6635.507267] Call Trace:[ 6635.507290] [<8025e724>] 0x8025e724[ 6635.521960] [<8000abf4>] 0x8000abf4[ 6635.525515] [<8000abfc>] 0x8000abfc[ 6635.529050] [<8001d990>] 0x8001d990[ 6635.541211] [<c00b1258>] 0xc00b1258[ 6635.544767] [<c00b1258>] 0xc00b1258[ 6635.548302] [<c00b1258>] 0xc00b1258[ 6635.562011] [<8001da04>] 0x8001da04[ 6635.565574] [<c00af0c0>] 0xc00af0c0[ 6635.569108] [<80406134>] 0x80406134[ 6635.579120] [<c00b1258>] 0xc00b1258[ 6635.588795] [<c00b12c4>] 0xc00b12c4[ 6635.593036] [<802c9c5c>] 0x802c9c5c[ 6635.596590] [<802c991c>] 0x802c991c[ 6635.600126] [<802c9dc0>] 0x802c9dc0[ 6635.615364] [<802c86e0>] 0x802c86e0[ 6635.618920] [<8007849c>] 0x8007849c[ 6635.628652] [<800bc5a4>] 0x800bc5a4[ 6635.635599] [<8002ec50>] 0x8002ec50[ 6635.639157] [<8000f14c>] 0x8000f14c[ 6635.649356] [ 6635.650891] ---[ end trace a60217f8a7ca79ca ]---but system seems functional and even Ethernet works (if I reload the module).
I would like to understand a bit better what's really happening.
Documentation pointers and explanations welcome.