ACK: [SRU][J][PATCH 0/1] CVE-2024-57982

[Andrei Gherzan]

On 26/09/09 04:29AM, Cengiz Can via kernel-team wrote:
> https://ubuntu.com/security/CVE-2024-57982
> 
> [ Impact ]
> 
> In the Linux kernel, the following vulnerability has been resolved:
> 
> xfrm: state: fix out-of-bounds read during lookup
> 
> lookup and resize can run in parallel.
> 
> The xfrm_state_hash_generation seqlock ensures a retry, but the hash functions
> can observe a hmask value that is too large for the new hlist array.
> 
> rehash does: rcu_assign_pointer(net->xfrm.state_bydst, ndst) [..]
> net->xfrm.state_hmask = nhashmask;
> 
> While state lookup does: h = xfrm_dst_hash(net, daddr, saddr, tmpl->reqid,
> encap_family); hlist_for_each_entry_rcu(x, net->xfrm.state_bydst + h, bydst) {
> 
> This is only safe in case the update to state_bydst is larger than
> net->xfrm.xfrm_state_hmask (or if the lookup function gets serialized via state
> spinlock again).
> 
> Fix this by prefetching state_hmask and the associated pointers. The
> xfrm_state_hash_generation seqlock retry will ensure that the pointer and the
> hmask will be consistent.
> 
> The existing helpers, like xfrm_dst_hash(), are now unsafe for RCU side, add
> lockdep assertions to document that they are only safe for insert side.
> 
> xfrm_state_lookup_byaddr() uses the spinlock rather than RCU. AFAICS this is an
> oversight from back when state lookup was converted to RCU, this lock should be
> replaced with RCU in a future patch.
> 
> [ Fix ]
> 
> jammy/linux: backported from e952837f3ddb
> 
> [ Test Plan ]
> 
> Build and boot tested.
> 
> [ Where Problems Could Occur ]
> 
> A bad fix would primarily affect systems that use the IPsec transformation
> (xfrm) state layer, such as hosts running IPsec/VPN tunnels or other SA-based
> traffic where the state database is resized under concurrent lookups; a
> regression here could manifest as incorrect state lookups or crashes on those
> networking paths. Systems that do not use IPsec/xfrm are not affected.
> 
> [ Other Info ]
> 
> Kybele flow-v11-21-g0f091652. Reference: b779a6f2/v1

Acked-by: Andrei Gherzan <andrei.gherzan at canonical.com>

-- 
Andrei Gherzan
gpg: rsa4096/D4D94F67AD0E9640
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