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[114.36.226.49]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82a072419efsm6286702b3a.11.2026.03.13.06.01.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Mar 2026 06:01:12 -0700 (PDT) Date: Fri, 13 Mar 2026 21:01:08 +0800 From: Hao-Yu Yang To: Eric Dumazet Cc: Peter Zijlstra , security@kernel.org, tglx@kernel.org, mingo@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] futex: Use-after-free between futex_key_to_node_opt and vma_replace_policy Message-ID: References: <20260313123940.51301-1-naup96721@gmail.com> <20260313125259.GB2872@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Fri, Mar 13, 2026 at 01:55:07PM +0100, Eric Dumazet wrote: > On Fri, Mar 13, 2026 at 1:53 PM Peter Zijlstra wrote: > > > > On Fri, Mar 13, 2026 at 08:39:40PM +0800, Hao-Yu Yang wrote: > > > 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. > > > > > > > > I would try and trim that trace, there is a lot of stuff that isn't > > really relevant. > > > > > Fix by adding rcu to __mpol_put(). > > > > > > Fixes: c042c505210d ("futex: Implement FUTEX2_MPOL") > > > Reported-by: Hao-Yu Yang > > > Signed-off-by: Hao-Yu Yang > > > > I would further suggest: > > > > Suggested-by: Eric Dumazet > > Reviewed-by: Eric Dumazet > > > > > But yeah, other than that: > > > > Acked-by: Peter Zijlstra (Intel) > > Thanks Sorry, should I not have resent the entire patch? I just cc stable when I resent the entire patch.