NACK/Cmnt: [PATCH 0/8 v2][B/F/G/OEM-5.6/OEM-5.10 v3] CVE-2021-29650: xtables membarrier DoS

[Stefan Bader]

On 08.04.21 20:40, Tim Gardner wrote:
> v2 - Update Groovy patches. Add Focal, OEM-5.10
> v3 - Embed release name in patch subject.
> 
> [SRU Justification]
> 
> An issue was discovered in the Linux kernel before 5.11.11. The netfilter
> subsystem allows attackers to cause a denial of service (panic) because
> net/netfilter/x_tables.c and include/linux/netfilter/x_tables.h lack a
> full memory barrier upon the assignment of a new table value, aka CID-175e476b8cdf.
> 
> This DOS has existed since v3.0. It was partially mitigated by
> cc00bcaa589914096edef7fb87ca5cee4a166b5c ("netfilter: x_tables: Switch
> synchronization to RCU") in v5.10, but was then reverted in v5.12 which restored the
> full DOS vulnerability. Hence the fix commit 175e476b8cdf2a4de7432583b49c871345e4f8a1
> in v5.12.
> 
> Focal, Groovy, and OEM-5.6 required (Revert "netfilter: x_tables: Switch
> synchronization to RCU") in order to cleanly apply "netfilter: x_tables: Use correct
> memory barriers.".
> 
> [Test Plan]
> None - this one is quite difficult to reproduce. It was tested on a 4 core MIPS.
> 
> [Where problems could occur]
> At most this patch might introduce a performance reduction, though
> upstream testing has not been able to detect any. Upstream seems
> confident that reverting the RCU patch and applying the write barrier
> patch was the right thing to do.
> 
> [Other Info]
> None
> 
> When looking at upstream, this seems to require 2 reverts. The second being a 
fixup for the RCU one:

commit abe7034b9a8d57737e80cc16d60ed3666990bdbf
Author: Mark Tomlinson <mark.tomlinson at alliedtelesis.co.nz>
Date:   Mon Mar 8 14:24:11 2021 +1300

     Revert "netfilter: x_tables: Update remaining dereference to RCU"

     This reverts commit 443d6e86f821a165fae3fc3fc13086d27ac140b1.

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