In the Linux kernel, the following vulnerability has been resolved: xfrm: use hlist_del_init_rcu…

Why it is Yellow

• CVSS 7.0 high
• On your watchlist: linux kernel

References

• https://git.kernel.org/stable/c/2afb8dc1f4390f164db8352f8e685e126e9db566
• https://git.kernel.org/stable/c/4748c27e2e6a1969e02f1df46e62f79d2799b80b
• https://git.kernel.org/stable/c/9b74a47a4cbd0d29faff4f3b199212c73e6b6220
• https://git.kernel.org/stable/c/fb38fb7420d5f7192f9e2b6ac835ede149cd7ac5

Original description

In the Linux kernel, the following vulnerability has been resolved: xfrm: use hlist_del_init_rcu for state_cache and state_cache_input Commit 14acf9652e56 ("xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete") converted bydst/bysrc/byseq/byspi from hlist_del_rcu() to hlist_del_init_rcu() so that a second __xfrm_state_delete() on the same object becomes a no-op rather than a write through LIST_POISON pprev. It missed state_cache and state_cache_input, which kept hlist_del_rcu(): - hlist_del_rcu() leaves pprev = LIST_POISON2 (non-NULL), so hlist_unhashed() returns false. - hlist_del_init_rcu() leaves pprev = NULL, so hlist_unhashed() returns true. A second __xfrm_state_delete() therefore enters __hlist_del() on the already-deleted state_cache/state_cache_input nodes and does WRITE_ONCE(*pprev, next) through LIST_POISON2 — a write use-after-free once the slab is reused. The corruption can in turn cause a subsequent hlist_for_each_entry_rcu traversal to follow a dangling next pointer, producing the read use-after-free reported in xfrm_input_state_lookup(). Switch state_cache and state_cache_input to hlist_del_init_rcu() to match the other four lists, closing the write use-after-free and, with it, the read use-after-free it spawns.