Date: Wed, 14 Nov 2012 09:14:11 -0800 From: Greg KH <gregkh@...uxfoundation.org> To: oss-security@...ts.openwall.com Subject: Re: Linux kernel handling of IPv6 temporary addresses On Wed, Nov 14, 2012 at 10:43:22AM +0200, George Kargiotakis wrote: > Hello all, > > Due to the way the Linux kernel handles the creation of IPv6 temporary > addresses a malicious LAN user can remotely disable them altogether > which may lead to privacy violations and information disclosure. > > By default the Linux kernel uses the 'ipv6.max_addresses' option to > specify how many IPv6 addresses an interface may have. The > 'ipv6.regen_max_retry' option specifies how many times the kernel will > try to create a new address. > > Currently, in net/ipv6/addrconf.c,lines 898-910, there is no > distinction between the events of reaching max_addresses for an > interface and failing to generate a new address. Upon > reaching any of the above conditions the following error is emitted by > the kernel times 'regen_max_retry' (default value 3): > > [183.793393] ipv6_create_tempaddr(): retry temporary address > regeneration [183.793405] ipv6_create_tempaddr(): retry temporary > address regeneration [183.793411] ipv6_create_tempaddr(): retry > temporary address regeneration > > After 'regen_max_retry' is reached the kernel completely disables > temporary address generation for that interface. > > [183.793413] ipv6_create_tempaddr(): regeneration time exceeded - > disabled temporary address support > > RFC4941 3.3.7 specifies that disabling temp_addresses MUST happen upon > failure to create non-unique addresses which is not the above case. > Addresses would have been created if the kernel had a higher > 'ipv6.max_addresses' limit. > > A malicious LAN user can send a limited amount of RA prefixes and thus > disable IPv6 temporary address creation for any Linux host. Recent > distributions which enable the IPv6 Privacy extensions by default, like > Ubuntu 12.04 and 12.10, are vulnerable to such attacks. > > Due to the kernel's default values for valid (604800) and preferred > (86400) lifetimes, this scenario may even occur under normal usage when > a Router sends both a public and a ULA prefix, which is not an uncommon > scenario for IPv6. 16 addresses are not enough with the current default > timers when more than 1 prefix is advertised. > > The kernel should at least differentiate between the two cases of > reaching max_addresses and being unable to create new addresses, due to > DAD conflicts for example. Have you discussed this with the upstream Linux kernel networking developers? thanks, greg k-h
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