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authorDavid Ahern <dsahern@gmail.com>2019-09-30 20:28:34 -0700
committerDavid S. Miller <davem@davemloft.net>2019-10-01 21:43:41 -0400
commita3ce2a21bb8969ae27917281244fa91bf5f286d7 (patch)
treee974aeca11dd2309164642b599c62c7edd2381cb /net/rfkill
parent3256a2d6ab1f71f9a1bd2d7f6f18eb8108c48d17 (diff)
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ipv6: Handle race in addrconf_dad_work
Rajendra reported a kernel panic when a link was taken down: [ 6870.263084] BUG: unable to handle kernel NULL pointer dereference at 00000000000000a8 [ 6870.271856] IP: [<ffffffff8efc5764>] __ipv6_ifa_notify+0x154/0x290 <snip> [ 6870.570501] Call Trace: [ 6870.573238] [<ffffffff8efc58c6>] ? ipv6_ifa_notify+0x26/0x40 [ 6870.579665] [<ffffffff8efc98ec>] ? addrconf_dad_completed+0x4c/0x2c0 [ 6870.586869] [<ffffffff8efe70c6>] ? ipv6_dev_mc_inc+0x196/0x260 [ 6870.593491] [<ffffffff8efc9c6a>] ? addrconf_dad_work+0x10a/0x430 [ 6870.600305] [<ffffffff8f01ade4>] ? __switch_to_asm+0x34/0x70 [ 6870.606732] [<ffffffff8ea93a7a>] ? process_one_work+0x18a/0x430 [ 6870.613449] [<ffffffff8ea93d6d>] ? worker_thread+0x4d/0x490 [ 6870.619778] [<ffffffff8ea93d20>] ? process_one_work+0x430/0x430 [ 6870.626495] [<ffffffff8ea99dd9>] ? kthread+0xd9/0xf0 [ 6870.632145] [<ffffffff8f01ade4>] ? __switch_to_asm+0x34/0x70 [ 6870.638573] [<ffffffff8ea99d00>] ? kthread_park+0x60/0x60 [ 6870.644707] [<ffffffff8f01ae77>] ? ret_from_fork+0x57/0x70 [ 6870.650936] Code: 31 c0 31 d2 41 b9 20 00 08 02 b9 09 00 00 0 addrconf_dad_work is kicked to be scheduled when a device is brought up. There is a race between addrcond_dad_work getting scheduled and taking the rtnl lock and a process taking the link down (under rtnl). The latter removes the host route from the inet6_addr as part of addrconf_ifdown which is run for NETDEV_DOWN. The former attempts to use the host route in ipv6_ifa_notify. If the down event removes the host route due to the race to the rtnl, then the BUG listed above occurs. This scenario does not occur when the ipv6 address is not kept (net.ipv6.conf.all.keep_addr_on_down = 0) as addrconf_ifdown sets the state of the ifp to DEAD. Handle when the addresses are kept by checking IF_READY which is reset by addrconf_ifdown. The 'dead' flag for an inet6_addr is set only under rtnl, in addrconf_ifdown and it means the device is getting removed (or IPv6 is disabled). The interesting cases for changing the idev flag are addrconf_notify (NETDEV_UP and NETDEV_CHANGE) and addrconf_ifdown (reset the flag). The former does not have the idev lock - only rtnl; the latter has both. Based on that the existing dead + IF_READY check can be moved to right after the rtnl_lock in addrconf_dad_work. Fixes: f1705ec197e7 ("net: ipv6: Make address flushing on ifdown optional") Reported-by: Rajendra Dendukuri <rajendra.dendukuri@broadcom.com> Signed-off-by: David Ahern <dsahern@gmail.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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