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[114.36.226.49]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c73ebb76cc1sm1819845a12.27.2026.03.13.05.07.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Mar 2026 05:07:35 -0700 (PDT) From: Hao-Yu Yang To: security@kernel.org Cc: tglx@kernel.org, mingo@redhat.com, linux-kernel@vger.kernel.org, Hao-Yu Yang Subject: [PATCH v1] futex: Use-after-free between futex_key_to_node_opt and vma_replace_policy Date: Fri, 13 Mar 2026 20:05:29 +0800 Message-Id: <20260313120529.46754-1-naup96721@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 (kern= el/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-g0257= f64bdac7 #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 ./includ= e/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/fu= tex/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/entr= y/syscall_64.c:94) [ 151.417342] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:1= 30) [ 151.418312] I don't really know how to fix this vulnerability. So this patch just initial attempt to patch and need more discussion. I think we need to remove this path or add some lock. Fixes: c042c505210d ("futex: Implement FUTEX2_MPOL") Reported-by: Hao-Yu Yang Signed-off-by: Hao-Yu Yang --- kernel/futex/core.c | 23 ----------------------- 1 file changed, 23 deletions(-) diff --git a/kernel/futex/core.c b/kernel/futex/core.c index cf7e610eac42..0b44fcb30268 100644 --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -362,31 +362,8 @@ static int __futex_key_to_node(struct mm_struct *mm, u= nsigned long addr) return node; } =20 -static int futex_key_to_node_opt(struct mm_struct *mm, unsigned long addr) -{ - int seq, node; - - guard(rcu)(); - - if (!mmap_lock_speculate_try_begin(mm, &seq)) - return -EBUSY; - - node =3D __futex_key_to_node(mm, addr); - - if (mmap_lock_speculate_retry(mm, seq)) - return -EAGAIN; - - return node; -} - static int futex_mpol(struct mm_struct *mm, unsigned long addr) { - int node; - - node =3D futex_key_to_node_opt(mm, addr); - if (node >=3D FUTEX_NO_NODE) - return node; - guard(mmap_read_lock)(mm); return __futex_key_to_node(mm, addr); } --=20 2.34.1