CVE-2024-50036 — net: do not delay dst_entries_add() in dst_release()

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

net: do not delay dst_entries_add() in dst_release()

dst_entries_add() uses per-cpu data that might be freed at netns dismantle from ip6_route_net_exit() calling dst_entries_destroy()

Before ip6_route_net_exit() can be called, we release all the dsts associated with this netns, via calls to dst_release(), which waits an rcu grace period before calling dst_destroy()

dst_entries_add() use in dst_destroy() is racy, because dst_entries_destroy() could have been called already.

Decrementing the number of dsts must happen sooner.

Notes:

1) in CONFIG_XFRM case, dst_destroy() can call dst_release_immediate(child), this might also cause UAF if the child does not have DST_NOCOUNT set. IPSEC maintainers might take a look and see how to address this.

2) There is also discussion about removing this count of dst, which might happen in future kernels.

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CVE-2024-50036 — net: do not delay dst_entries_add() in dst_release()