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[114.36.226.49]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2aece6198dfsm23053715ad.29.2026.03.13.05.51.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Mar 2026 05:51:22 -0700 (PDT) Date: Fri, 13 Mar 2026 20:51:19 +0800 From: Hao-Yu Yang To: Greg KH Cc: 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> <2026031349-aging-colonize-39a0@gregkh> 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=us-ascii Content-Disposition: inline In-Reply-To: <2026031349-aging-colonize-39a0@gregkh> On Fri, Mar 13, 2026 at 01:44:23PM +0100, Greg KH 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. > > As this is sent to lkml in public, no need to get security@k.o involved. > > > [ 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 > > [ 151.414476] > > [ 151.415431] CPU: 1 UID: 1000 PID: 87 Comm: e Not tainted 7.0.0-rc3-g0257f64bdac7 #1 PREEMPT(lazy) > > [ 151.415758] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 > > [ 151.415969] Call Trace: > > [ 151.416059] > > [ 151.416161] dump_stack_lvl (lib/dump_stack.c:123) > > [ 151.416299] print_report (mm/kasan/report.c:379 mm/kasan/report.c:482) > > [ 151.416359] ? __virt_addr_valid (./include/linux/mmzone.h:2046 ./include/linux/mmzone.h:2198 arch/x86/mm/physaddr.c:54) > > [ 151.416412] ? __futex_key_to_node (kernel/futex/core.c:349) > > [ 151.416517] ? kasan_complete_mode_report_info (mm/kasan/report_generic.c:182) > > [ 151.416583] ? __futex_key_to_node (kernel/futex/core.c:349) > > [ 151.416631] kasan_report (mm/kasan/report.c:597) > > [ 151.416677] ? __futex_key_to_node (kernel/futex/core.c:349) > > [ 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) > > [ 151.416871] ? __pfx_get_futex_key (kernel/futex/core.c:550) > > [ 151.416927] futex_wake (kernel/futex/waitwake.c:165) > > [ 151.416976] ? __pfx_futex_wake (kernel/futex/waitwake.c:156) > > [ 151.417022] ? __pfx___x64_sys_futex_wait (kernel/futex/syscalls.c:398) > > [ 151.417081] __x64_sys_futex_wake (kernel/futex/syscalls.c:382 kernel/futex/syscalls.c:366 kernel/futex/syscalls.c:366) > > [ 151.417129] x64_sys_call (arch/x86/entry/syscall_64.c:41) > > [ 151.417236] do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94) > > [ 151.417342] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) > > [ 151.418312] > > > > Fix by adding rcu to __mpol_put(). > > > > change-log: > > v2-v1: add rcu to __mpol_put > > This goes below the --- line. > > > > > Fixes: c042c505210d ("futex: Implement FUTEX2_MPOL") > > Reported-by: Hao-Yu Yang > > Signed-off-by: Hao-Yu Yang > > --- > > No cc: stable? > > thanks, > > greg k-h Oh, I forgot. I have resend this patch and cc to stable.