Messages in this thread | | | Date | Wed, 7 Nov 2018 19:17:51 -0500 | From | Sasha Levin <> | Subject | Re: [PATCH] [stable, netdev 4.4+] lan78xx: make sure RX_ADDRL & RX_ADDRH regs are always up to date |
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On Wed, Nov 07, 2018 at 05:50:57PM +0100, Paolo Pisati wrote: >[partial backport upstream 760db29bdc97b73ff60b091315ad787b1deb5cf5] > >Upon invocation, lan78xx_init_mac_address() checks that the mac address present >in the RX_ADDRL & RX_ADDRH registers is a valid address, if not, it first tries >to read a new address from an external eeprom or the otp area, and in case both >read fail (or the address read back is invalid), it randomly generates a new >one. > >Unfortunately, due to the way the above logic is laid out, >if both read_eeprom() and read_otp() fail, a new mac address is correctly >generated but is never written back to RX_ADDRL & RX_ADDRH, leaving the chip in an >incosistent state and with an invalid mac address (e.g. the nic appears to be >completely dead, and doesn't receive any packet, etc): > >lan78xx_init_mac_address() >... >if (lan78xx_read_eeprom(addr ...) || lan78xx_read_otp(addr ...)) { > if (is_valid_ether_addr(addr) { > // nop... > } else { > random_ether_addr(addr); > } > > // correctly writes back the new address > lan78xx_write_reg(RX_ADDRL, addr ...); > lan78xx_write_reg(RX_ADDRH, addr ...); >} else { > // XXX if both eeprom and otp read fail, we land here and skip > // XXX the RX_ADDRL & RX_ADDRH update completely > random_ether_addr(addr); >} > >This bug went unnoticed because lan78xx_read_otp() was buggy itself and would >never fail, up until 4bfc338 "lan78xx: Correctly indicate invalid OTP" >fixed it and as a side effect uncovered this bug. > >4.18+ is fine, since the bug was implicitly fixed in 760db29 "lan78xx: Read MAC >address from DT if present" when the address change logic was reorganized, but >it's still present in all stable trees below that: linux-4.4.y, linux-4.9.y, >linux-4.14.y, etc up to linux-4.18.y (not included). > >Signed-off-by: Paolo Pisati <p.pisati@gmail.com>
So why not just take 760db29bdc completely? It looks safer than taking a partial backport, and will make applying future patches easier.
I tried to do it and it doesn't look like there are any dependencies that would cause an issue.
-- Thanks, Sasha
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