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 2E2D0233933; Wed, 20 May 2026 16:33:25 +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=1779294807; cv=none; b=h6F2JfTPSe8zCgJnMe03RoDlh8LL9wDJXeL9inCg8F3nKrNP+/44mIaqQtb4KPdlTM7Z2/gIwXmOfHuzbJOOsCLwaMf9h4oRPYY3ahAveANUg2N0I3gpovaepDVitkqc+V5V+tPOP2PsCrg6vnUDUiZilpIYllyVpvi+KXTT9fw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779294807; c=relaxed/simple; bh=AmlGzCPbPUAgE5r5pDLTuNLvievl1E0f4+71lLOQBGE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=lhGeNsZPGLNMiclp2FyxsdGtYiBqHlDr+IhNCRcyB2KOur4bOJLAFl3Op3NjgiEkrenIY3Jyw+1Hy9BG4n98C5x0lIsliigZhNF31rqZR0f7xRsWbE9+aFRwVEJn2t/ZZAg/6/wDRikgc3d4YJxEVI97UI78PUeGztaqTKiDmh4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=P4FRKt8/; 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="P4FRKt8/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 448691F000E9; Wed, 20 May 2026 16:33:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1779294805; bh=X+1RResyZwNdW/PvfP/IDVaicn70q0yDJwgrv8jjKDs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=P4FRKt8/LxQ+jz86i8P2Nqq12+6avM4Yozr5c/9f9I45vT5kDDRBOgNsrRg38c/f3 z6qvZFvjOsqE1gqkz9jcTwuY/jf7XE3fybTQMgvRWXmCmoXZuE8CKJIcSZpBz9JzIF DpJ4VNlTbyzA5m3zQDV9nLOW9gDc9jR9Ka++4++E= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Puranjay Mohan , Alexei Starovoitov , Sasha Levin Subject: [PATCH 7.0 0180/1146] bpf: fix mm lifecycle in open-coded task_vma iterator Date: Wed, 20 May 2026 18:07:10 +0200 Message-ID: <20260520162152.354211154@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260520162148.390695140@linuxfoundation.org> References: <20260520162148.390695140@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 7.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Puranjay Mohan [ Upstream commit d8e27d2d22b6e2df3a0125b8c08e9aace38c954c ] The open-coded task_vma iterator reads task->mm locklessly and acquires mmap_read_trylock() but never calls mmget(). If the task exits concurrently, the mm_struct can be freed as it is not SLAB_TYPESAFE_BY_RCU, resulting in a use-after-free. Safely read task->mm with a trylock on alloc_lock and acquire an mm reference. Drop the reference via bpf_iter_mmput_async() in _destroy() and error paths. bpf_iter_mmput_async() is a local wrapper around mmput_async() with a fallback to mmput() on !CONFIG_MMU. Reject irqs-disabled contexts (including NMI) up front. Operations used by _next() and _destroy() (mmap_read_unlock, bpf_iter_mmput_async) take spinlocks with IRQs disabled (pool->lock, pi_lock). Running from NMI or from a tracepoint that fires with those locks held could deadlock. A trylock on alloc_lock is used instead of the blocking task_lock() (get_task_mm) to avoid a deadlock when a softirq BPF program iterates a task that already holds its alloc_lock on the same CPU. Fixes: 4ac454682158 ("bpf: Introduce task_vma open-coded iterator kfuncs") Signed-off-by: Puranjay Mohan Link: https://lore.kernel.org/r/20260408154539.3832150-2-puranjay@kernel.org Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- kernel/bpf/task_iter.c | 54 +++++++++++++++++++++++++++++++++++++++--- 1 file changed, 51 insertions(+), 3 deletions(-) diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c index 98d9b4c0daff3..c1f5fbe9dc2f3 100644 --- a/kernel/bpf/task_iter.c +++ b/kernel/bpf/task_iter.c @@ -9,6 +9,7 @@ #include #include #include +#include #include "mmap_unlock_work.h" static const char * const iter_task_type_names[] = { @@ -794,6 +795,15 @@ const struct bpf_func_proto bpf_find_vma_proto = { .arg5_type = ARG_ANYTHING, }; +static inline void bpf_iter_mmput_async(struct mm_struct *mm) +{ +#ifdef CONFIG_MMU + mmput_async(mm); +#else + mmput(mm); +#endif +} + struct bpf_iter_task_vma_kern_data { struct task_struct *task; struct mm_struct *mm; @@ -825,6 +835,24 @@ __bpf_kfunc int bpf_iter_task_vma_new(struct bpf_iter_task_vma *it, BUILD_BUG_ON(sizeof(struct bpf_iter_task_vma_kern) != sizeof(struct bpf_iter_task_vma)); BUILD_BUG_ON(__alignof__(struct bpf_iter_task_vma_kern) != __alignof__(struct bpf_iter_task_vma)); + /* bpf_iter_mmput_async() needs mmput_async() which requires CONFIG_MMU */ + if (!IS_ENABLED(CONFIG_MMU)) { + kit->data = NULL; + return -EOPNOTSUPP; + } + + /* + * Reject irqs-disabled contexts including NMI. Operations used + * by _next() and _destroy() (mmap_read_unlock, bpf_iter_mmput_async) + * can take spinlocks with IRQs disabled (pi_lock, pool->lock). + * Running from NMI or from a tracepoint that fires with those + * locks held could deadlock. + */ + if (irqs_disabled()) { + kit->data = NULL; + return -EBUSY; + } + /* is_iter_reg_valid_uninit guarantees that kit hasn't been initialized * before, so non-NULL kit->data doesn't point to previously * bpf_mem_alloc'd bpf_iter_task_vma_kern_data @@ -834,7 +862,25 @@ __bpf_kfunc int bpf_iter_task_vma_new(struct bpf_iter_task_vma *it, return -ENOMEM; kit->data->task = get_task_struct(task); + /* + * Safely read task->mm and acquire an mm reference. + * + * Cannot use get_task_mm() because its task_lock() is a + * blocking spin_lock that would deadlock if the target task + * already holds alloc_lock on this CPU (e.g. a softirq BPF + * program iterating a task interrupted while holding its + * alloc_lock). + */ + if (!spin_trylock(&task->alloc_lock)) { + err = -EBUSY; + goto err_cleanup_iter; + } kit->data->mm = task->mm; + if (kit->data->mm && !(task->flags & PF_KTHREAD)) + mmget(kit->data->mm); + else + kit->data->mm = NULL; + spin_unlock(&task->alloc_lock); if (!kit->data->mm) { err = -ENOENT; goto err_cleanup_iter; @@ -844,15 +890,16 @@ __bpf_kfunc int bpf_iter_task_vma_new(struct bpf_iter_task_vma *it, irq_work_busy = bpf_mmap_unlock_get_irq_work(&kit->data->work); if (irq_work_busy || !mmap_read_trylock(kit->data->mm)) { err = -EBUSY; - goto err_cleanup_iter; + goto err_cleanup_mmget; } vma_iter_init(&kit->data->vmi, kit->data->mm, addr); return 0; +err_cleanup_mmget: + bpf_iter_mmput_async(kit->data->mm); err_cleanup_iter: - if (kit->data->task) - put_task_struct(kit->data->task); + put_task_struct(kit->data->task); bpf_mem_free(&bpf_global_ma, kit->data); /* NULL kit->data signals failed bpf_iter_task_vma initialization */ kit->data = NULL; @@ -875,6 +922,7 @@ __bpf_kfunc void bpf_iter_task_vma_destroy(struct bpf_iter_task_vma *it) if (kit->data) { bpf_mmap_unlock_mm(kit->data->work, kit->data->mm); put_task_struct(kit->data->task); + bpf_iter_mmput_async(kit->data->mm); bpf_mem_free(&bpf_global_ma, kit->data); } } -- 2.53.0