From patchwork Wed Jan 18 13:47:07 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Bartosz Golaszewski X-Patchwork-Id: 644838 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AFDACC32793 for ; Wed, 18 Jan 2023 14:08:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230024AbjAROIo (ORCPT ); Wed, 18 Jan 2023 09:08:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34934 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229872AbjAROIY (ORCPT ); Wed, 18 Jan 2023 09:08:24 -0500 Received: from mail-wr1-x42e.google.com (mail-wr1-x42e.google.com [IPv6:2a00:1450:4864:20::42e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A0EA846149 for ; Wed, 18 Jan 2023 05:47:12 -0800 (PST) Received: by mail-wr1-x42e.google.com with SMTP id b5so12820337wrn.0 for ; Wed, 18 Jan 2023 05:47:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bgdev-pl.20210112.gappssmtp.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=fr8Gz55U4TOXGvBsDrDEZEh2Yy8w/FVFBooraq51kv0=; b=1uWwE4GmTr+03g5OABkJY6AGMGvrTIc7r5VQlFTSF6dZdeoJgMAIe707XW2VPiAXqd J5GQYsPG2cw1ziqfrWhZNDCo+2n6w1bheWrJYUi+PQsAwJoIUB1FJNPHNksb7JMWNTyy V7kjVnIlEnkpgy8qAvEvIzq6UgmfbxcgqNYlYFlhGrSoQU7ojU0Rm/qNE/7SXOSE2GqI KFQcfmO3wo4Wctn6opMfzgqVmIB60ev9yCJCJ7o1DmgBT7PBt3PmVva9M8wlICiJoBWj OOvhZ8oXXUTi7kmCGgUvSOHYBuZwpjU2WMk4gDvUBCYZ7SL9/z5R8uYYa6DfcYKoGBmR oN9Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=fr8Gz55U4TOXGvBsDrDEZEh2Yy8w/FVFBooraq51kv0=; b=5Qp66WsKuiS1XMvScl648n4RZUv8+f3YtUw/TNSrdLyuKrqc3l2dZN7ol4ZC3/9O1W 8g2h1MEYfZVNus0ALGbgKblsWYth252wahD3vKqxC1evYQOc6gNuLGyieu9pnw/DBSDE yjxnrbFN5itm74res6LiVQal70Ducgq1Wb4ReMrVmOGXMd6pn99O+8O4HVaVkycJwkGx mQaRx7RnuZcAOKUHWaHr1qLI9hzsVr/70WGrhZyK7k4JjAgn0k41QzvxhtNwgCTKnp9x xiGSzVmVjLuhELXIKBrzx9DgNikDW2mxPywyltytcDcyw7o/M5fmRpboFTzSROrqiK4g BqvQ== X-Gm-Message-State: AFqh2krx7Y60zqOsil1iJOSaTIr7ezHV9qp5Qf0E/9md3PNGzDxnKDL5 9uR+8eunNx+5YAnU3KVZMQpsxw== X-Google-Smtp-Source: AMrXdXsdim4iXuQyaIhNNQC4T1V90BS13OCnv/Ybnk9psMXZ+Tr3WU7q4bIjazUhCn6G9S1T8D+ElQ== X-Received: by 2002:a5d:5b0e:0:b0:250:22e4:b89e with SMTP id bx14-20020a5d5b0e000000b0025022e4b89emr7147933wrb.65.1674049630910; Wed, 18 Jan 2023 05:47:10 -0800 (PST) Received: from brgl-uxlite.home ([2a01:cb1d:334:ac00:1866:5d91:a429:aba]) by smtp.gmail.com with ESMTPSA id t18-20020adff612000000b002be2f18938csm1562150wrp.41.2023.01.18.05.47.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Jan 2023 05:47:10 -0800 (PST) From: Bartosz Golaszewski To: Wolfram Sang Cc: linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org, Bartosz Golaszewski Subject: [PATCH v2] i2c: dev: don't allow user-space to deadlock the kernel Date: Wed, 18 Jan 2023 14:47:07 +0100 Message-Id: <20230118134707.239900-1-brgl@bgdev.pl> X-Mailer: git-send-email 2.37.2 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org From: Bartosz Golaszewski If we open an i2c character device and then unbind the underlying i2c adapter (either by unbinding it manually via sysfs or - for a real-life example - when unplugging a USB device with an i2c adaper), the kernel thread calling i2c_del_adapter() will become blocked waiting for the completion that only completes once all references to the character device get dropped. In order to fix that, we introduce a couple changes. They need to be part of a single commit in order to preserve bisectability. First, drop the dev_release completion. That removes the risk of a deadlock but we now need to protect the character device structures against NULL pointer dereferences. To that end introduce an rw semaphore. It will protect the dummy i2c_client structure against dropping the adapter from under it. It will be taken for reading by all file_operations callbacks and for writing by the notifier's unbind handler. This way we don't prohibit the syscalls that don't get in each other's way from running concurrently but the adapter will not be unbound before all syscalls return. Finally: upon being notified about an unbind event for the i2c adapter, we take the lock for writing and set the adapter pointer in the character device's structure to NULL. This "numbs down" the device - it still exists but is no longer functional. Meanwhile every syscall callback checks that pointer after taking the lock but before executing any code that requires it. If it's NULL, we return an error to user-space. This way we can safely open an i2c device from user-space, unbind the device without triggering a deadlock and any subsequent system-call for the file descriptor associated with the removed adapter will gracefully fail. Signed-off-by: Bartosz Golaszewski --- v1 -> v2: - make symbol names more descriptive - protect the name_show() sysfs callback too - zero the adapter's struct device on device release - make sure the code works nicely with CONFIG_DEBUG_KOBJECT_RELEASE enabled drivers/i2c/i2c-core-base.c | 32 ++++------- drivers/i2c/i2c-dev.c | 109 +++++++++++++++++++++++++++++++----- include/linux/i2c.h | 2 - 3 files changed, 106 insertions(+), 37 deletions(-) diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c index 087e480b624c..ec8140d907c2 100644 --- a/drivers/i2c/i2c-core-base.c +++ b/drivers/i2c/i2c-core-base.c @@ -1139,7 +1139,17 @@ EXPORT_SYMBOL_GPL(i2c_new_ancillary_device); static void i2c_adapter_dev_release(struct device *dev) { struct i2c_adapter *adap = to_i2c_adapter(dev); - complete(&adap->dev_released); + + /* free bus id */ + mutex_lock(&core_lock); + idr_remove(&i2c_adapter_idr, adap->nr); + mutex_unlock(&core_lock); + + /* + * Clear the device structure in case this adapter is ever going to be + * added again. + */ + memset(&adap->dev, 0, sizeof(adap->dev)); } unsigned int i2c_adapter_depth(struct i2c_adapter *adapter) @@ -1512,9 +1522,7 @@ static int i2c_register_adapter(struct i2c_adapter *adap) return 0; out_reg: - init_completion(&adap->dev_released); device_unregister(&adap->dev); - wait_for_completion(&adap->dev_released); out_list: mutex_lock(&core_lock); idr_remove(&i2c_adapter_idr, adap->nr); @@ -1713,25 +1721,7 @@ void i2c_del_adapter(struct i2c_adapter *adap) i2c_host_notify_irq_teardown(adap); - /* wait until all references to the device are gone - * - * FIXME: This is old code and should ideally be replaced by an - * alternative which results in decoupling the lifetime of the struct - * device from the i2c_adapter, like spi or netdev do. Any solution - * should be thoroughly tested with DEBUG_KOBJECT_RELEASE enabled! - */ - init_completion(&adap->dev_released); device_unregister(&adap->dev); - wait_for_completion(&adap->dev_released); - - /* free bus id */ - mutex_lock(&core_lock); - idr_remove(&i2c_adapter_idr, adap->nr); - mutex_unlock(&core_lock); - - /* Clear the device structure in case this adapter is ever going to be - added again */ - memset(&adap->dev, 0, sizeof(adap->dev)); } EXPORT_SYMBOL(i2c_del_adapter); diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c index 107623c4cc14..38c83ee408be 100644 --- a/drivers/i2c/i2c-dev.c +++ b/drivers/i2c/i2c-dev.c @@ -28,6 +28,7 @@ #include #include #include +#include #include #include @@ -44,8 +45,14 @@ struct i2c_dev { struct i2c_adapter *adap; struct device dev; struct cdev cdev; + struct rw_semaphore rwsem; }; +static inline struct i2c_dev *inode_to_i2c_dev(struct inode *ino) +{ + return container_of(ino->i_cdev, struct i2c_dev, cdev); +} + #define I2C_MINORS (MINORMASK + 1) static LIST_HEAD(i2c_dev_list); static DEFINE_SPINLOCK(i2c_dev_list_lock); @@ -99,10 +106,21 @@ static ssize_t name_show(struct device *dev, struct device_attribute *attr, char *buf) { struct i2c_dev *i2c_dev = i2c_dev_get_by_minor(MINOR(dev->devt)); + const char *name; if (!i2c_dev) return -ENODEV; - return sysfs_emit(buf, "%s\n", i2c_dev->adap->name); + + down_read(&i2c_dev->rwsem); + if (!i2c_dev->adap) { + up_read(&i2c_dev->rwsem); + return -ENODEV; + } + + name = i2c_dev->adap->name; + up_read(&i2c_dev->rwsem); + + return sysfs_emit(buf, "%s\n", name); } static DEVICE_ATTR_RO(name); @@ -136,15 +154,23 @@ static ssize_t i2cdev_read(struct file *file, char __user *buf, size_t count, { char *tmp; int ret; - + struct i2c_dev *i2c_dev = inode_to_i2c_dev(file_inode(file)); struct i2c_client *client = file->private_data; if (count > 8192) count = 8192; + down_read(&i2c_dev->rwsem); + if (!i2c_dev->adap) { + up_read(&i2c_dev->rwsem); + return -ENODEV; + } + tmp = kzalloc(count, GFP_KERNEL); - if (tmp == NULL) + if (tmp == NULL) { + up_read(&i2c_dev->rwsem); return -ENOMEM; + } pr_debug("i2c-%d reading %zu bytes.\n", iminor(file_inode(file)), count); @@ -152,6 +178,7 @@ static ssize_t i2cdev_read(struct file *file, char __user *buf, size_t count, if (ret >= 0) if (copy_to_user(buf, tmp, ret)) ret = -EFAULT; + up_read(&i2c_dev->rwsem); kfree(tmp); return ret; } @@ -161,18 +188,28 @@ static ssize_t i2cdev_write(struct file *file, const char __user *buf, { int ret; char *tmp; + struct i2c_dev *i2c_dev = inode_to_i2c_dev(file_inode(file)); struct i2c_client *client = file->private_data; if (count > 8192) count = 8192; + down_read(&i2c_dev->rwsem); + if (!i2c_dev->adap) { + up_read(&i2c_dev->rwsem); + return -ENODEV; + } + tmp = memdup_user(buf, count); - if (IS_ERR(tmp)) + if (IS_ERR(tmp)) { + up_read(&i2c_dev->rwsem); return PTR_ERR(tmp); + } pr_debug("i2c-%d writing %zu bytes.\n", iminor(file_inode(file)), count); ret = i2c_master_send(client, tmp, count); + up_read(&i2c_dev->rwsem); kfree(tmp); return ret; } @@ -389,7 +426,8 @@ static noinline int i2cdev_ioctl_smbus(struct i2c_client *client, return res; } -static long i2cdev_ioctl(struct file *file, unsigned int cmd, unsigned long arg) +static long i2cdev_ioctl_unlocked(struct file *file, unsigned int cmd, + unsigned long arg) { struct i2c_client *client = file->private_data; unsigned long funcs; @@ -495,6 +533,20 @@ static long i2cdev_ioctl(struct file *file, unsigned int cmd, unsigned long arg) return 0; } +static long i2cdev_ioctl(struct file *file, unsigned int cmd, unsigned long arg) +{ + struct i2c_dev *i2c_dev = inode_to_i2c_dev(file_inode(file)); + long ret; + + down_read(&i2c_dev->rwsem); + if (!i2c_dev->adap) + ret = -ENODEV; + else + ret = i2cdev_ioctl_unlocked(file, cmd, arg); + up_read(&i2c_dev->rwsem); + + return ret; +} #ifdef CONFIG_COMPAT struct i2c_smbus_ioctl_data32 { @@ -516,10 +568,12 @@ struct i2c_rdwr_ioctl_data32 { u32 nmsgs; }; -static long compat_i2cdev_ioctl(struct file *file, unsigned int cmd, unsigned long arg) +static long compat_i2cdev_ioctl_unlocked(struct file *file, unsigned int cmd, + unsigned long arg) { struct i2c_client *client = file->private_data; unsigned long funcs; + switch (cmd) { case I2C_FUNCS: funcs = i2c_get_functionality(client->adapter); @@ -578,19 +632,39 @@ static long compat_i2cdev_ioctl(struct file *file, unsigned int cmd, unsigned lo return i2cdev_ioctl(file, cmd, arg); } } + +static long compat_i2cdev_ioctl(struct file *file, unsigned int cmd, + unsigned long arg) +{ + struct i2c_dev *i2c_dev = inode_to_i2c_dev(file_inode(file)); + long ret; + + down_read(&i2c_dev->rwsem); + if (!i2c_dev->adap) + ret = -ENODEV; + else + ret = compat_i2cdev_ioctl_unlocked(file, cmd, arg); + up_read(&i2c_dev->rwsem); + + return ret; +} #else #define compat_i2cdev_ioctl NULL #endif static int i2cdev_open(struct inode *inode, struct file *file) { - unsigned int minor = iminor(inode); + struct i2c_dev *i2c_dev = inode_to_i2c_dev(inode); struct i2c_client *client; struct i2c_adapter *adap; + int ret = 0; - adap = i2c_get_adapter(minor); - if (!adap) - return -ENODEV; + down_read(&i2c_dev->rwsem); + adap = i2c_dev->adap; + if (!adap) { + ret = -ENODEV; + goto out_unlock; + } /* This creates an anonymous i2c_client, which may later be * pointed to some address using I2C_SLAVE or I2C_SLAVE_FORCE. @@ -601,22 +675,23 @@ static int i2cdev_open(struct inode *inode, struct file *file) */ client = kzalloc(sizeof(*client), GFP_KERNEL); if (!client) { - i2c_put_adapter(adap); - return -ENOMEM; + ret = -ENOMEM; + goto out_unlock; } snprintf(client->name, I2C_NAME_SIZE, "i2c-dev %d", adap->nr); client->adapter = adap; file->private_data = client; - return 0; +out_unlock: + up_read(&i2c_dev->rwsem); + return ret; } static int i2cdev_release(struct inode *inode, struct file *file) { struct i2c_client *client = file->private_data; - i2c_put_adapter(client->adapter); kfree(client); file->private_data = NULL; @@ -669,6 +744,8 @@ static int i2cdev_attach_adapter(struct device *dev, void *dummy) i2c_dev->dev.parent = &adap->dev; i2c_dev->dev.release = i2cdev_dev_release; + init_rwsem(&i2c_dev->rwsem); + res = dev_set_name(&i2c_dev->dev, "i2c-%d", adap->nr); if (res) goto err_put_i2c_dev; @@ -698,6 +775,10 @@ static int i2cdev_detach_adapter(struct device *dev, void *dummy) if (!i2c_dev) /* attach_adapter must have failed */ return NOTIFY_DONE; + down_write(&i2c_dev->rwsem); + i2c_dev->adap = NULL; + up_write(&i2c_dev->rwsem); + put_i2c_dev(i2c_dev, true); pr_debug("adapter [%s] unregistered\n", adap->name); diff --git a/include/linux/i2c.h b/include/linux/i2c.h index d84e0e99f084..3f31e4032044 100644 --- a/include/linux/i2c.h +++ b/include/linux/i2c.h @@ -14,7 +14,6 @@ #include #include #include /* for struct device */ -#include /* for completion */ #include #include #include @@ -739,7 +738,6 @@ struct i2c_adapter { int nr; char name[48]; - struct completion dev_released; struct mutex userspace_clients_lock; struct list_head userspace_clients;