netdev - IPv4/IPv6 sysctl unregistration deadlock

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 25 Feb 2009 06:23:33 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Linux Netdev List <netdev@...r.kernel.org>
CC:	Herbert Xu <herbert@...dor.apana.org.au>
Subject: IPv4/IPv6 sysctl unregistration deadlock

Ben Greear reported sporadically hanging ip processes when adding or
removing MACVLAN devices, which seem to be caused by a race between
sysctl handling and device notifiers.

What is happening is:

Process 1:

- "ip" deletes a macvlan device (or any other kind of device gets
   removed for whatever reason)
- netdev notifier chain notifies IPv6 addrconf while holding the RTNL

Process 2:

- a different process writes something to /proc/sys/net/ipv6/forwarding
- sysctl table is marked as busy, addrconf_sysctl_forward() is invoked
- tries to take rtnl, waits for process 1

Process 1:

- IPv6 begins sysctl unregistration, which is deferred using a
   completion until the table is not busy anymore (=> waiting for
   process 2)

At this point both processes are deadlocked. Judging by a quick look,
IPv4 seems to have the exact same problem.

An easy fix would be to keep track of whether sysctl unregistration
is in progress in IPv4/IPv6 and ignore new requests from that point
on. Its not very elegant though, so I was wondering whether anyone
has a better suggestion.

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html