CVE-2026-23415 — futex: Fix UaF between futex_key_to_node_opt() and vma_replace_policy()

Affected: Linux

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

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().

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CVE-2026-23415 — futex: Fix UaF between futex_key_to_node_opt() and vma_replace_policy()