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

[Cengiz Can]

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