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([2405:201:682f:383f:e530:e1cf:b5ff:83e4]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3153e044912sm4182791eec.15.2026.07.31.02.13.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 31 Jul 2026 02:13:31 -0700 (PDT) From: Deepanshu Kartikey To: gregkh@linuxfoundation.org Cc: viro@zeniv.linux.org.uk, jack@suse.cz, brauner@kernel.org, mjguzik@gmail.com, kees@kernel.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, Deepanshu Kartikey , syzbot+df9e891bf8ea586f846b@syzkaller.appspotmail.com Subject: [PATCH] usb: gadgetfs: fix use-after-free in ep_open() Date: Fri, 31 Jul 2026 14:43:16 +0530 Message-ID: <20260731091316.14145-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ep_open() dereferenced inode->i_private and locked its embedded mutex before checking whether the underlying ep_data was still alive. destroy_ep_files(), called from gadgetfs_unbind(), can free that same ep_data concurrently, since nothing prevented an in-flight open() from racing the teardown. KASAN reports a slab-use-after-free in ep_open(), with the object freed by a concurrent gadgetfs_unbind() -> destroy_ep_files() -> put_ep() -> kfree(). Fix it by adding an inode back-pointer to ep_data, having destroy_ep_files() clear inode->i_private to NULL under dev->lock before the object can be freed, and having ep_open() read inode->i_private and pin the result with get_ep() under that same lock, bailing out with -ENOENT if it finds NULL. This makes liveness self-evident at the point of use instead of being inferred from device state, so it holds regardless of which path frees the endpoint. gadgetfs_create_file() gains an optional inode-out parameter so activate_ep_files() can capture the inode it creates; the ep0 caller in gadgetfs_fill_super() passes NULL, since dev_data is unaffected by this fix. Reported-by: syzbot+df9e891bf8ea586f846b@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=df9e891bf8ea586f846b Signed-off-by: Deepanshu Kartikey --- drivers/usb/gadget/legacy/inode.c | 51 +++++++++++++++++++++---------- 1 file changed, 35 insertions(+), 16 deletions(-) diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c index d87a8ab51510..f566b2ec7c38 100644 --- a/drivers/usb/gadget/legacy/inode.c +++ b/drivers/usb/gadget/legacy/inode.c @@ -207,6 +207,7 @@ struct ep_data { struct usb_endpoint_descriptor desc, hs_desc; struct list_head epfiles; wait_queue_head_t wait; + struct inode *inode; }; static inline void get_ep (struct ep_data *data) @@ -235,6 +236,7 @@ static void put_ep (struct ep_data *data) static const char *CHIP; static DEFINE_MUTEX(sb_mutex); /* Serialize superblock operations */ +static struct dev_data *the_device; /*----------------------------------------------------------------------*/ @@ -817,25 +819,39 @@ ep_config (struct ep_data *data, const char *buf, size_t len) static int ep_open (struct inode *inode, struct file *fd) { - struct ep_data *data = inode->i_private; - int value = -EBUSY; + struct dev_data *dev = the_device; + struct ep_data *data; + int value = -ENODEV; + + spin_lock_irq(&dev->lock); + data = inode->i_private; + if (data == NULL) { + spin_unlock_irq(&dev->lock); + return -ENOENT; + } + get_ep(data); + spin_unlock_irq(&dev->lock); - if (mutex_lock_interruptible(&data->lock) != 0) + if (mutex_lock_interruptible(&data->lock) != 0) { + put_ep(data); return -EINTR; - spin_lock_irq (&data->dev->lock); - if (data->dev->state == STATE_DEV_UNBOUND) + } + + value = -EBUSY; + spin_lock_irq(&dev->lock); + if (dev->state == STATE_DEV_UNBOUND) value = -ENOENT; else if (data->state == STATE_EP_DISABLED) { value = 0; data->state = STATE_EP_READY; - get_ep (data); fd->private_data = data; - VDEBUG (data->dev, "%s ready\n", data->name); + VDEBUG(dev, "%s ready\n", data->name); } else - DBG (data->dev, "%s state %d\n", - data->name, data->state); - spin_unlock_irq (&data->dev->lock); + DBG(dev, "%s state %d\n", data->name, data->state); + spin_unlock_irq(&dev->lock); mutex_unlock(&data->lock); + if (value) + put_ep(data); return value; } @@ -1563,6 +1579,7 @@ static void destroy_ep_files (struct dev_data *dev) /* break link to FS */ ep = list_first_entry (&dev->epfiles, struct ep_data, epfiles); list_del_init (&ep->epfiles); + ep->inode->i_private = NULL; spin_unlock_irq (&dev->lock); /* break link to controller */ @@ -1588,7 +1605,8 @@ static void destroy_ep_files (struct dev_data *dev) static int gadgetfs_create_file (struct super_block *sb, char const *name, - void *data, const struct file_operations *fops); + void *data, const struct file_operations *fops, + struct inode **inode_out); static int activate_ep_files (struct dev_data *dev) { @@ -1618,7 +1636,7 @@ static int activate_ep_files (struct dev_data *dev) goto enomem1; err = gadgetfs_create_file (dev->sb, data->name, - data, &ep_io_operations); + data, &ep_io_operations, &data->inode); if (err) goto enomem2; list_add_tail (&data->epfiles, &dev->epfiles); @@ -1663,8 +1681,6 @@ gadgetfs_unbind (struct usb_gadget *gadget) put_dev (dev); } -static struct dev_data *the_device; - static int gadgetfs_bind(struct usb_gadget *gadget, struct usb_gadget_driver *driver) { @@ -1984,7 +2000,7 @@ gadgetfs_make_inode (struct super_block *sb, * so inode and dentry are paired, until device reconfig. */ static int gadgetfs_create_file (struct super_block *sb, char const *name, - void *data, const struct file_operations *fops) + void *data, const struct file_operations *fops, struct inode **inode_out) { struct dentry *dentry; struct inode *inode; @@ -1994,6 +2010,9 @@ static int gadgetfs_create_file (struct super_block *sb, char const *name, if (!inode) return -ENOMEM; + if (inode_out) + *inode_out = inode; + dentry = simple_start_creating(sb->s_root, name); if (IS_ERR(dentry)) { iput(inode); @@ -2056,7 +2075,7 @@ gadgetfs_fill_super (struct super_block *sb, struct fs_context *fc) goto Enomem; dev->sb = sb; - rc = gadgetfs_create_file(sb, CHIP, dev, &ep0_operations); + rc = gadgetfs_create_file(sb, CHIP, dev, &ep0_operations, NULL); if (rc) { put_dev(dev); goto Enomem; -- 2.43.0