From 190a8c48ff623c3d67cb295b4536a660db2012aa Mon Sep 17 00:00:00 2001 From: Hao-Yu Yang Date: Fri, 13 Mar 2026 20:47:56 +0800 Subject: futex: Fix UaF between futex_key_to_node_opt() and vma_replace_policy() During futex_key_to_node_opt() execution, vma->vm_policy is read under speculative mmap lock and RCU. Concurrently, mbind() may call vma_replace_policy() which frees the old mempolicy immediately via kmem_cache_free(). This creates a race where __futex_key_to_node() dereferences a freed mempolicy pointer, causing a use-after-free read of mpol->mode. [ 151.412631] BUG: KASAN: slab-use-after-free in __futex_key_to_node (kernel/futex/core.c:349) [ 151.414046] Read of size 2 at addr ffff888001c49634 by task e/87 [ 151.415969] Call Trace: [ 151.416732] __asan_load2 (mm/kasan/generic.c:271) [ 151.416777] __futex_key_to_node (kernel/futex/core.c:349) [ 151.416822] get_futex_key (kernel/futex/core.c:374 kernel/futex/core.c:386 kernel/futex/core.c:593) Fix by adding rcu to __mpol_put(). Fixes: c042c505210d ("futex: Implement FUTEX2_MPOL") Reported-by: Hao-Yu Yang Suggested-by: Eric Dumazet Signed-off-by: Hao-Yu Yang Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Eric Dumazet Acked-by: David Hildenbrand (Arm) Link: https://patch.msgid.link/20260324174418.GB1850007@noisy.programming.kicks-ass.net --- include/linux/mempolicy.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include') diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h index 0fe96f3ab3ef..65c732d440d2 100644 --- a/include/linux/mempolicy.h +++ b/include/linux/mempolicy.h @@ -55,6 +55,7 @@ struct mempolicy { nodemask_t cpuset_mems_allowed; /* relative to these nodes */ nodemask_t user_nodemask; /* nodemask passed by user */ } w; + struct rcu_head rcu; }; /* -- cgit v1.2.3