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 C67303F7ABC; Wed, 20 May 2026 18:05:03 +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=1779300305; cv=none; b=O+aWYTbly5ilKEK7sXXIKOcnP6YcBMXOG66tYh4hkmiyRhoUIHw7N2QhSUYau4YqWKTvgFKOiA2IztMBPjaex+XSZP/i9qh5V9pp88Oq2K1OdjLSBGg/OZ66izDWwKIYWjDm6D62xamRWj7WzKRvMxQIqBcxtEOE1CPUsY63NUg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779300305; c=relaxed/simple; bh=D116QIVzwNJ1R9qGzLgM9iVxiXfGIs71hHQ/GePZ7w0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=B9Jr8W31Z28SIC/Zup41Lymq/L7E65gOrtjOm2z9uxcCrasBGxuU390Jgo07AV3jRPf52wGgb5T37QjTNu11B+RO6ULl/ikg7YECnqt407pj0SBu2Zv/OXvho8WI/VJzd2dOPPHVk8YSF1NH9JbQ/aOONIPMIGMl8BaJtjmiUEY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Omrgk03u; 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="Omrgk03u" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 313071F000E9; Wed, 20 May 2026 18:05:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1779300303; bh=WCmpAbw8RvehdQEiEJoyeDsJp9vN2Bg9JgCUSEamg6g=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Omrgk03urNEEk6QAlAL2TJPS/Ek0EBGA9Jp4aUuhWNZEQeFGZExt3e034W/LAwRx1 O7eEQjudBU3RkapywlfYpgop1CsAG5Q8udrjEuAed6MArxNPuqBCK0C17cWFboX8sy mdLQVv0S0ctQbzjd771WV9WDC/CezyKtLGX91qSE= 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 6.12 082/666] bpf: fix mm lifecycle in open-coded task_vma iterator Date: Wed, 20 May 2026 18:14:53 +0200 Message-ID: <20260520162113.008301510@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260520162111.222830634@linuxfoundation.org> References: <20260520162111.222830634@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: 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 5af9e130e500f..c37ae44bd0a53 100644 --- a/kernel/bpf/task_iter.c +++ b/kernel/bpf/task_iter.c @@ -10,6 +10,7 @@ #include #include #include +#include #include "mmap_unlock_work.h" static const char * const iter_task_type_names[] = { @@ -798,6 +799,15 @@ 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; @@ -829,6 +839,24 @@ __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 @@ -838,7 +866,25 @@ __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; @@ -848,15 +894,16 @@ __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; @@ -879,6 +926,7 @@ __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