From patchwork Mon May 2 03:49:04 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tetsuo Handa X-Patchwork-Id: 569200 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 C8C71C433EF for ; Mon, 2 May 2022 03:49:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349288AbiEBDwm (ORCPT ); Sun, 1 May 2022 23:52:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38042 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229650AbiEBDwl (ORCPT ); Sun, 1 May 2022 23:52:41 -0400 Received: from www262.sakura.ne.jp (www262.sakura.ne.jp [202.181.97.72]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9EAD559BBB for ; Sun, 1 May 2022 20:49:11 -0700 (PDT) Received: from fsav315.sakura.ne.jp (fsav315.sakura.ne.jp [153.120.85.146]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 2423n9Fi010374; Mon, 2 May 2022 12:49:09 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav315.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav315.sakura.ne.jp); Mon, 02 May 2022 12:49:09 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav315.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 2423n8v4010364 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Mon, 2 May 2022 12:49:09 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Message-ID: <21ffa07a-1bc1-cb1f-eef4-6c3a73953061@I-love.SAKURA.ne.jp> Date: Mon, 2 May 2022 12:49:04 +0900 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Subject: [PATCH v2 (resend)] media: imon: reorganize serialization Content-Language: en-US From: Tetsuo Handa To: Sean Young , Alan Stern , Mauro Carvalho Chehab Cc: Jarod Wilson , syzbot , andreyknvl@google.com, linux-media@vger.kernel.org, linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com References: <00000000000043b599058faf0145@google.com> <5a06c7f1-9a29-99e4-c700-fec3f09509d2@I-love.SAKURA.ne.jp> <62dddbb9-3053-f284-f9db-3beda5e8e951@I-love.SAKURA.ne.jp> <349f3e34-41ed-f832-3b22-ae10c50e3868@I-love.SAKURA.ne.jp> In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Since usb_register_dev() from imon_init_display() from imon_probe() holds minor_rwsem while display_open() which holds driver_lock and ictx->lock is called with minor_rwsem held from usb_open(), holding driver_lock or ictx->lock when calling usb_register_dev() causes circular locking dependency problem. Since usb_deregister_dev() from imon_disconnect() holds minor_rwsem while display_open() which holds driver_lock is called with minor_rwsem held, holding driver_lock when calling usb_deregister_dev() also causes circular locking dependency problem. Sean Young explained that the problem is there are imon devices which have two usb interfaces, even though it is one device. The probe and disconnect function of both usb interfaces can run concurrently. Alan Stern responded that the driver and USB cores guarantee that when an interface is probed, both the interface and its USB device are locked. Ditto for when the disconnect callback gets run. So concurrent probing/ disconnection of multiple interfaces on the same device is not possible. Therefore, we don't need locks for handling race between imon_probe() and imon_disconnect(). But we still need to handle race between display_open() /vfd_write()/lcd_write()/display_close() and imon_disconnect(), for disconnect event can happen while file descriptors are in use. Since "struct file"->private_data is set by display_open(), vfd_write()/ lcd_write()/display_close() can assume that "struct file"->private_data is not NULL even after usb_set_intfdata(interface, NULL) was called. Replace insufficiently held driver_lock with refcount_t based management. Add a boolean flag for recording whether imon_disconnect() was already called. Use RCU for accessing this boolean flag and refcount_t. Since the boolean flag for imon_disconnect() is shared, disconnect event on either intf0 or intf1 affects both interfaces. But I assume that this change does not matter, for usually disconnect event would not happen while interfaces are in use. Link: https://syzkaller.appspot.com/bug?extid=c558267ad910fc494497 Reported-by: syzbot Signed-off-by: Tetsuo Handa Tested-by: syzbot Cc: Sean Young Cc: Alan Stern --- Changes in v2: Defer free_imon_context() using refcount till display_close() is called. drivers/media/rc/imon.c | 99 +++++++++++++++++++---------------------- 1 file changed, 47 insertions(+), 52 deletions(-) diff --git a/drivers/media/rc/imon.c b/drivers/media/rc/imon.c index 54da6f60079b..9a4f24e294bc 100644 --- a/drivers/media/rc/imon.c +++ b/drivers/media/rc/imon.c @@ -153,6 +153,24 @@ struct imon_context { const struct imon_usb_dev_descr *dev_descr; /* device description with key */ /* table for front panels */ + /* + * Fields for deferring free_imon_context(). + * + * Since reference to "struct imon_context" is stored into + * "struct file_operations"->private_data, we need to remember + * how many file descriptors might access this "struct imon_context". + */ + refcount_t users; + /* + * Use a flag for telling display_open()/vfd_write()/lcd_write() that + * imon_disconnect() was already called. + */ + bool disconnected; + /* + * We need to wait for RCU grace period in order to allow + * display_open() to safely check ->disconnected and increment ->users. + */ + struct rcu_head rcu; }; #define TOUCH_TIMEOUT (HZ/30) @@ -160,18 +178,18 @@ struct imon_context { /* vfd character device file operations */ static const struct file_operations vfd_fops = { .owner = THIS_MODULE, - .open = &display_open, - .write = &vfd_write, - .release = &display_close, + .open = display_open, + .write = vfd_write, + .release = display_close, .llseek = noop_llseek, }; /* lcd character device file operations */ static const struct file_operations lcd_fops = { .owner = THIS_MODULE, - .open = &display_open, - .write = &lcd_write, - .release = &display_close, + .open = display_open, + .write = lcd_write, + .release = display_close, .llseek = noop_llseek, }; @@ -439,9 +457,6 @@ static struct usb_driver imon_driver = { .id_table = imon_usb_id_table, }; -/* to prevent races between open() and disconnect(), probing, etc */ -static DEFINE_MUTEX(driver_lock); - /* Module bookkeeping bits */ MODULE_AUTHOR(MOD_AUTHOR); MODULE_DESCRIPTION(MOD_DESC); @@ -481,9 +496,11 @@ static void free_imon_context(struct imon_context *ictx) struct device *dev = ictx->dev; usb_free_urb(ictx->tx_urb); + WARN_ON(ictx->dev_present_intf0); usb_free_urb(ictx->rx_urb_intf0); + WARN_ON(ictx->dev_present_intf1); usb_free_urb(ictx->rx_urb_intf1); - kfree(ictx); + kfree_rcu(ictx, rcu); dev_dbg(dev, "%s: iMON context freed\n", __func__); } @@ -499,9 +516,6 @@ static int display_open(struct inode *inode, struct file *file) int subminor; int retval = 0; - /* prevent races with disconnect */ - mutex_lock(&driver_lock); - subminor = iminor(inode); interface = usb_find_interface(&imon_driver, subminor); if (!interface) { @@ -509,13 +523,16 @@ static int display_open(struct inode *inode, struct file *file) retval = -ENODEV; goto exit; } - ictx = usb_get_intfdata(interface); - if (!ictx) { + rcu_read_lock(); + ictx = usb_get_intfdata(interface); + if (!ictx || ictx->disconnected || !refcount_inc_not_zero(&ictx->users)) { + rcu_read_unlock(); pr_err("no context found for minor %d\n", subminor); retval = -ENODEV; goto exit; } + rcu_read_unlock(); mutex_lock(&ictx->lock); @@ -533,8 +550,10 @@ static int display_open(struct inode *inode, struct file *file) mutex_unlock(&ictx->lock); + if (retval && refcount_dec_and_test(&ictx->users)) + free_imon_context(ictx); + exit: - mutex_unlock(&driver_lock); return retval; } @@ -544,16 +563,9 @@ static int display_open(struct inode *inode, struct file *file) */ static int display_close(struct inode *inode, struct file *file) { - struct imon_context *ictx = NULL; + struct imon_context *ictx = file->private_data; int retval = 0; - ictx = file->private_data; - - if (!ictx) { - pr_err("no context for device\n"); - return -ENODEV; - } - mutex_lock(&ictx->lock); if (!ictx->display_supported) { @@ -568,6 +580,8 @@ static int display_close(struct inode *inode, struct file *file) } mutex_unlock(&ictx->lock); + if (refcount_dec_and_test(&ictx->users)) + free_imon_context(ictx); return retval; } @@ -934,15 +948,12 @@ static ssize_t vfd_write(struct file *file, const char __user *buf, int offset; int seq; int retval = 0; - struct imon_context *ictx; + struct imon_context *ictx = file->private_data; static const unsigned char vfd_packet6[] = { 0x01, 0x00, 0x00, 0x00, 0x00, 0xFF, 0xFF }; - ictx = file->private_data; - if (!ictx) { - pr_err_ratelimited("no context for device\n"); + if (ictx->disconnected) return -ENODEV; - } mutex_lock(&ictx->lock); @@ -1018,13 +1029,10 @@ static ssize_t lcd_write(struct file *file, const char __user *buf, size_t n_bytes, loff_t *pos) { int retval = 0; - struct imon_context *ictx; + struct imon_context *ictx = file->private_data; - ictx = file->private_data; - if (!ictx) { - pr_err_ratelimited("no context for device\n"); + if (ictx->disconnected) return -ENODEV; - } mutex_lock(&ictx->lock); @@ -2404,7 +2412,6 @@ static int imon_probe(struct usb_interface *interface, int ifnum, sysfs_err; int ret = 0; struct imon_context *ictx = NULL; - struct imon_context *first_if_ctx = NULL; u16 vendor, product; usbdev = usb_get_dev(interface_to_usbdev(interface)); @@ -2416,17 +2423,12 @@ static int imon_probe(struct usb_interface *interface, dev_dbg(dev, "%s: found iMON device (%04x:%04x, intf%d)\n", __func__, vendor, product, ifnum); - /* prevent races probing devices w/multiple interfaces */ - mutex_lock(&driver_lock); - first_if = usb_ifnum_to_if(usbdev, 0); if (!first_if) { ret = -ENODEV; goto fail; } - first_if_ctx = usb_get_intfdata(first_if); - if (ifnum == 0) { ictx = imon_init_intf0(interface, id); if (!ictx) { @@ -2434,9 +2436,11 @@ static int imon_probe(struct usb_interface *interface, ret = -ENODEV; goto fail; } + refcount_set(&ictx->users, 1); } else { /* this is the secondary interface on the device */ + struct imon_context *first_if_ctx = usb_get_intfdata(first_if); /* fail early if first intf failed to register */ if (!first_if_ctx) { @@ -2450,14 +2454,13 @@ static int imon_probe(struct usb_interface *interface, ret = -ENODEV; goto fail; } + refcount_inc(&ictx->users); } usb_set_intfdata(interface, ictx); if (ifnum == 0) { - mutex_lock(&ictx->lock); - if (product == 0xffdc && ictx->rf_device) { sysfs_err = sysfs_create_group(&interface->dev.kobj, &imon_rf_attr_group); @@ -2468,21 +2471,17 @@ static int imon_probe(struct usb_interface *interface, if (ictx->display_supported) imon_init_display(ictx, interface); - - mutex_unlock(&ictx->lock); } dev_info(dev, "iMON device (%04x:%04x, intf%d) on usb<%d:%d> initialized\n", vendor, product, ifnum, usbdev->bus->busnum, usbdev->devnum); - mutex_unlock(&driver_lock); usb_put_dev(usbdev); return 0; fail: - mutex_unlock(&driver_lock); usb_put_dev(usbdev); dev_err(dev, "unable to register, err %d\n", ret); @@ -2498,10 +2497,8 @@ static void imon_disconnect(struct usb_interface *interface) struct device *dev; int ifnum; - /* prevent races with multi-interface device probing and display_open */ - mutex_lock(&driver_lock); - ictx = usb_get_intfdata(interface); + ictx->disconnected = true; dev = ictx->dev; ifnum = interface->cur_altsetting->desc.bInterfaceNumber; @@ -2542,11 +2539,9 @@ static void imon_disconnect(struct usb_interface *interface) } } - if (!ictx->dev_present_intf0 && !ictx->dev_present_intf1) + if (refcount_dec_and_test(&ictx->users)) free_imon_context(ictx); - mutex_unlock(&driver_lock); - dev_dbg(dev, "%s: iMON device (intf%d) disconnected\n", __func__, ifnum); }