From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BF46733F59A; Sat, 12 Sep 2026 12:11:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789215081; cv=none; b=qXSKl67s1LOr+Ql+baFDvbL51k0OvjjpuggEx33lEteLQKchJPCU5U8iCiESDxyw1r64LC+YNZMtgNWZpnYyBDwRgJ4viZE6VxAl/nr54mcz9GY9i6f59/EVE8f5WKRx5ICm6OHpUwO9xV3BOeOLKBYaHFk9i8JrCL25xMsqD30= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789215081; c=relaxed/simple; bh=mKdZ3lmczpLuvakwv9DGzUfgPW/VS0RgoMVWOVEd00E=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=eCEOlyEbImqZCQC8x6EAQtFe5fnGubVypxsoMJjk3eU2aY4Sh6V1cblWSy/UocYZMSNbs/e/w90uv/a8jFKPP1Y1agJYntAVM8BfahlzAOUIoPvHlyDmP8jos5v+Ed5T4BZo4oVQXCmuAuzqwG59thS7XjqQI2v44pp9J8/OW7U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=NzPNlNTY; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="NzPNlNTY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 794931F000FF; Sat, 12 Sep 2026 12:11:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789215080; bh=4XY/gmOgy58GGBkEpGKnTtT76/PlpNG72gJYa5FKtEA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=NzPNlNTY0RmQb86AlFFq0FggYmgJCY0vCZf9gN82j76HNCEgraoxfMSMaOKdI8CA+ Ew8wFQ9scWejdbukEQtB1nac+0OldVGcQiSSH0vNlBYo1mznICVV5LMsYWI7KeUE6c CR9aQA5Qw++JIXwveHzEDR0064to/Aqo9oSYxchs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Sanghyun Park , Puranjay Mohan , Yonghong Song , Kumar Kartikeya Dwivedi , Sasha Levin Subject: [PATCH 6.12 0457/1376] bpf: Fix use-after-free on mm_struct in bpf_find_vma() Date: Sat, 12 Sep 2026 08:48:03 +0200 Message-ID: <20260912065617.716828726@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065607.535295758@linuxfoundation.org> References: <20260912065607.535295758@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sanghyun Park [ Upstream commit 47b079e2117a2ee52e21f8b72935900c702fc0b5 ] bpf_find_vma() reads task->mm and calls mmap_read_trylock(mm) without holding a reference on the mm. On a foreign task, a concurrent exit_mm() can free the mm_struct between the lockless read and the trylock, resulting in a use-after-free. mm_struct is not SLAB_TYPESAFE_BY_RCU. For the current task, task->mm is stable. For a foreign task, pin the mm under task->alloc_lock and release it with mmput_async(), mirroring commit d8e27d2d22b6 ("bpf: fix mm lifecycle in open-coded task_vma iterator"). Use spin_trylock() instead of get_task_mm() so BPF context does not block on alloc_lock. Reject irqs-disabled contexts and !CONFIG_MMU on the foreign-task path because dropping the mm reference is not safe there. Race: CPU0 (BPF program) CPU1 (exiting task) ============================ ========================== bpf_find_vma(foreign_task): mm = task->mm exit_mm(): task->mm = NULL mmput(mm) -> frees mm_struct mmap_read_trylock(mm) // UAF on mm Fixes: 7c7e3d31e785 ("bpf: Introduce helper bpf_find_vma") Signed-off-by: Sanghyun Park Reviewed-by: Puranjay Mohan Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/20260708072106.199637-2-sanghyun.park.cnu@gmail.com Signed-off-by: Kumar Kartikeya Dwivedi Signed-off-by: Sasha Levin --- kernel/bpf/task_iter.c | 36 +++++++++++++++++++++++++++++++++--- 1 file changed, 33 insertions(+), 3 deletions(-) diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c index fc5f463ca529a..f3a7a96a77d7d 100644 --- a/kernel/bpf/task_iter.c +++ b/kernel/bpf/task_iter.c @@ -760,6 +760,7 @@ BPF_CALL_5(bpf_find_vma, struct task_struct *, task, u64, start, struct mmap_unlock_irq_work *work = NULL; struct vm_area_struct *vma; bool irq_work_busy = false; + bool __maybe_unused mmput_needed = false; struct mm_struct *mm; int ret = -ENOENT; @@ -769,14 +770,38 @@ BPF_CALL_5(bpf_find_vma, struct task_struct *, task, u64, start, if (!task) return -ENOENT; - mm = task->mm; + if (task == current) { + mm = task->mm; + } else { + /* + * Foreign task: pin task->mm against a concurrent exit_mm(). + * Use trylock on alloc_lock instead of get_task_mm()'s + * blocking task_lock() to avoid deadlocking the target task. + */ + if (!IS_ENABLED(CONFIG_MMU)) + return -EOPNOTSUPP; + if (irqs_disabled()) + return -EBUSY; + if (!spin_trylock(&task->alloc_lock)) + return -EBUSY; + mm = task->mm; + if (mm && !(task->flags & PF_KTHREAD)) { + mmget(mm); + mmput_needed = true; + } else { + mm = NULL; + } + spin_unlock(&task->alloc_lock); + } if (!mm) return -ENOENT; irq_work_busy = bpf_mmap_unlock_get_irq_work(&work); - if (irq_work_busy || !mmap_read_trylock(mm)) - return -EBUSY; + if (irq_work_busy || !mmap_read_trylock(mm)) { + ret = -EBUSY; + goto out; + } vma = find_vma(mm, start); @@ -786,6 +811,11 @@ BPF_CALL_5(bpf_find_vma, struct task_struct *, task, u64, start, ret = 0; } bpf_mmap_unlock_mm(work, mm); +out: +#ifdef CONFIG_MMU + if (mmput_needed) + mmput_async(mm); +#endif return ret; } -- 2.53.0