🛡️ CVE-2024-57982 — kernel

xfrm: state: fix out-of-bounds read during lookup

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.