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Wed, 01 Jul 2026 13:53:21 -0700 (PDT) Received: from localhost.localdomain ([2a01:4f9:2a:1c13::2]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-39b37fe594fsm2237911fa.31.2026.07.01.13.53.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jul 2026 13:53:20 -0700 (PDT) From: Melbin K Mathew To: gregkh@linuxfoundation.org Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, security@kernel.org, Melbin K Mathew , stable@vger.kernel.org Subject: [PATCH] usb: gadget: printer: fix infinite loop in printer_read() Date: Wed, 1 Jul 2026 22:53:20 +0200 Message-Id: <20260701205320.227791-1-mlbnkm1@gmail.com> X-Mailer: git-send-email 2.39.5 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit printer_read() uses the same variable for the requested copy size and the number of bytes actually copied to user space. copy_to_user() returns the number of bytes not copied, so when it fails to copy anything, the computed copied length becomes zero. In that case len, buf, current_rx_bytes and current_rx_buf are left unchanged. If RX data is available and the user buffer remains unwritable, the read loop can repeat indefinitely. Track the copied length separately and return -EFAULT, or the number of bytes already copied, if an iteration makes no progress. Fixes: b185f01a9ab7 ("usb: gadget: printer: factor out f_printer") Cc: stable@vger.kernel.org Signed-off-by: Melbin K Mathew --- A small userspace model/reproducer is available to maintainers on request. drivers/usb/gadget/function/f_printer.c | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c index e4f7828ae7..e346e4c26e 100644 --- a/drivers/usb/gadget/function/f_printer.c +++ b/drivers/usb/gadget/function/f_printer.c @@ -432,7 +432,7 @@ printer_read(struct file *fd, char __user *buf, size_t len, loff_t *ptr) { struct printer_dev *dev = fd->private_data; unsigned long flags; - size_t size; + size_t size, not_copied, copied; size_t bytes_copied; struct usb_request *req; /* This is a pointer to the current USB rx request. */ @@ -525,14 +525,16 @@ printer_read(struct file *fd, char __user *buf, size_t len, loff_t *ptr) else size = len; - size -= copy_to_user(buf, current_rx_buf, size); - bytes_copied += size; - len -= size; - buf += size; + not_copied = copy_to_user(buf, current_rx_buf, size); + copied = size - not_copied; + + bytes_copied += copied; + len -= copied; + buf += copied; spin_lock_irqsave(&dev->lock, flags); - /* We've disconnected or reset so return. */ + /* We have disconnected or reset so return. */ if (dev->reset_printer) { list_add(¤t_rx_req->list, &dev->rx_reqs); spin_unlock_irqrestore(&dev->lock, flags); @@ -543,6 +545,17 @@ printer_read(struct file *fd, char __user *buf, size_t len, loff_t *ptr) if (dev->interface < 0) goto out_disabled; + if (!copied) { + dev->current_rx_req = current_rx_req; + dev->current_rx_bytes = current_rx_bytes; + dev->current_rx_buf = current_rx_buf; + spin_unlock_irqrestore(&dev->lock, flags); + mutex_unlock(&dev->lock_printer_io); + return bytes_copied ? bytes_copied : -EFAULT; + } + + size = copied; + /* If we not returning all the data left in this RX request * buffer then adjust the amount of data left in the buffer. * Othewise if we are done with this RX request buffer then -- 2.39.5