Forwarded: Re: [syzbot] [usb?] general protection fault in adsl_state_store

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Subject: Re: [syzbot] [usb?] general protection fault in adsl_state_store
Author: jie.wang@xxxxxxxxx

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

diff --git a/drivers/usb/atm/cxacru.c b/drivers/usb/atm/cxacru.c
index 636f7886fc260..501a51b27e466 100644
--- a/drivers/usb/atm/cxacru.c
+++ b/drivers/usb/atm/cxacru.c
@@ -356,7 +356,7 @@ static ssize_t adsl_state_store(struct device *dev,
 	if (!strcmp(str_cmd, "stop") || !strcmp(str_cmd, "restart")) {
 		ret = cxacru_cm(instance, CM_REQUEST_CHIP_ADSL_LINE_STOP, NULL, 0, NULL, 0);
 		if (ret < 0) {
-			atm_err(instance->usbatm, "change adsl state:"
+			usb_err(instance->usbatm, "change adsl state:"
 				" CHIP_ADSL_LINE_STOP returned %d\n", ret);
 
 			ret = -EIO;
@@ -376,7 +376,7 @@ static ssize_t adsl_state_store(struct device *dev,
 	if (!strcmp(str_cmd, "start") || !strcmp(str_cmd, "restart")) {
 		ret = cxacru_cm(instance, CM_REQUEST_CHIP_ADSL_LINE_START, NULL, 0, NULL, 0);
 		if (ret < 0) {
-			atm_err(instance->usbatm, "change adsl state:"
+			usb_err(instance->usbatm, "change adsl state:"
 				" CHIP_ADSL_LINE_START returned %d\n", ret);
 
 			ret = -EIO;
@@ -396,6 +396,15 @@ static ssize_t adsl_state_store(struct device *dev,
 		poll = -1;
 	}
 
+	/* cxacru_poll_status() below dereferences atm_dev, which may not be
+	 * set up yet; reject before poll_state is advanced so that
+	 * cxacru_atm_start() can still start polling once it is.
+	 */
+	if (poll == CXPOLL_POLLING && !instance->usbatm->atm_dev) {
+		ret = -ENODEV;
+		poll = -1;
+	}
+
 	if (poll == CXPOLL_POLLING) {
 		mutex_lock(&instance->poll_state_serialize);
 		switch (instance->poll_state) {
@@ -481,7 +490,7 @@ static ssize_t adsl_config_store(struct device *dev,
 			ret = cxacru_cm(instance, CM_REQUEST_CARD_DATA_SET,
 				(u8 *) data, 4 + num * 8, NULL, 0);
 			if (ret < 0) {
-				atm_err(instance->usbatm,
+				usb_err(instance->usbatm,
 					"set card data returned %d\n", ret);
 				return -EIO;
 			}
@@ -490,7 +499,7 @@ static ssize_t adsl_config_store(struct device *dev,
 				snprintf(log + tmp*12, 13, " %02x=%08x",
 					le32_to_cpu(data[tmp * 2 + 1]),
 					le32_to_cpu(data[tmp * 2 + 2]));
-			atm_info(instance->usbatm, "config%s\n", log);
+			usb_info(instance->usbatm, "config%s\n", log);
 			num = 0;
 		}
 	}