Re: CVE-2024-39503: netfilter: ipset: Fix race between namespace cleanup and gc in the list:set type

[Siddh Raman Pant <siddh.raman.pant@oracle.com>]

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On Fri, 12 Jul 2024 14:21:09 +0200, Greg Kroah-Hartman wrote:
> In the Linux kernel, the following vulnerability has been resolved:
> 
> netfilter: ipset: Fix race between namespace cleanup and gc in the list:set type
> 
> Lion Ackermann reported that there is a race condition between namespace cleanup
> in ipset and the garbage collection of the list:set type. The namespace
> cleanup can destroy the list:set type of sets while the gc of the set type is
> waiting to run in rcu cleanup. The latter uses data from the destroyed set which
> thus leads use after free. The patch contains the following parts:
> 
> - When destroying all sets, first remove the garbage collectors, then wait
>   if needed and then destroy the sets.
> - Fix the badly ordered "wait then remove gc" for the destroy a single set
>   case.
> - Fix the missing rcu locking in the list:set type in the userspace test
>   case.
> - Use proper RCU list handlings in the list:set type.
> 
> The patch depends on c1193d9bbbd3 (netfilter: ipset: Add list flush to cancel_gc).

This commit does not exist in stable kernels. Please backport it.

	netfilter: ipset: Add list flush to cancel_gc
	
	Flushing list in cancel_gc drops references to other lists right away,
	without waiting for RCU to destroy list. Fixes race when referenced
	ipsets can't be destroyed while referring list is scheduled for destroy.

Since this is missing, the CVE fix potentially introduced new races as
it makes use of RCU.

Thanks,
Siddh

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