From: Vincent Mailhol mailhol.vincent@wanadoo.fr
Commit 7fdaf8966aae ("can: ucan: use strscpy() to instead of strncpy()") unintentionally introduced a one byte out of bound read on strscpy()'s source argument (which is kind of ironic knowing that strscpy() is meant to be a more secure alternative :)).
Let's consider below buffers:
dest[len + 1]; /* will be NUL terminated */ src[len]; /* may not be NUL terminated */
When doing:
strncpy(dest, src, len); dest[len] = '\0';
strncpy() will read up to len bytes from src.
On the other hand:
strscpy(dest, src, len + 1);
will read up to len + 1 bytes from src, that is to say, an out of bound read of one byte will occur on src if it is not NUL terminated. Note that the src[len] byte is never copied, but strscpy() still needs to read it to check whether a truncation occurred or not.
This exact pattern happened in ucan.
The root cause is that the source is not NUL terminated. Instead of doing a copy in a local buffer, directly NUL terminate it as soon as usb_control_msg() returns. With this, the local firmware_str[] variable can be removed.
On top of this do a couple refactors:
- ucan_ctl_payload->raw is only used for the firmware string, so rename it to ucan_ctl_payload->fw_str and change its type from u8 to char.
- ucan_device_request_in() is only used to retrieve the firmware string, so rename it to ucan_get_fw_str() and refactor it to make it directly handle all the string termination logic.
Reported-by: syzbot+d7d8c418e8317899e88c@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-can/67b323a4.050a0220.173698.002b.GAE@google.c... Fixes: 7fdaf8966aae ("can: ucan: use strscpy() to instead of strncpy()") Signed-off-by: Vincent Mailhol mailhol.vincent@wanadoo.fr Link: https://patch.msgid.link/20250218143515.627682-2-mailhol.vincent@wanadoo.fr Cc: stable@vger.kernel.org Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de --- drivers/net/can/usb/ucan.c | 43 ++++++++++++++++---------------------- 1 file changed, 18 insertions(+), 25 deletions(-)
diff --git a/drivers/net/can/usb/ucan.c b/drivers/net/can/usb/ucan.c index 39a63b7313a4..07406daf7c88 100644 --- a/drivers/net/can/usb/ucan.c +++ b/drivers/net/can/usb/ucan.c @@ -186,7 +186,7 @@ union ucan_ctl_payload { */ struct ucan_ctl_cmd_get_protocol_version cmd_get_protocol_version;
- u8 raw[128]; + u8 fw_str[128]; } __packed;
enum { @@ -424,18 +424,20 @@ static int ucan_ctrl_command_out(struct ucan_priv *up, UCAN_USB_CTL_PIPE_TIMEOUT); }
-static int ucan_device_request_in(struct ucan_priv *up, - u8 cmd, u16 subcmd, u16 datalen) +static void ucan_get_fw_str(struct ucan_priv *up, char *fw_str, size_t size) { - return usb_control_msg(up->udev, - usb_rcvctrlpipe(up->udev, 0), - cmd, - USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE, - subcmd, - 0, - up->ctl_msg_buffer, - datalen, - UCAN_USB_CTL_PIPE_TIMEOUT); + int ret; + + ret = usb_control_msg(up->udev, usb_rcvctrlpipe(up->udev, 0), + UCAN_DEVICE_GET_FW_STRING, + USB_DIR_IN | USB_TYPE_VENDOR | + USB_RECIP_DEVICE, + 0, 0, fw_str, size - 1, + UCAN_USB_CTL_PIPE_TIMEOUT); + if (ret > 0) + fw_str[ret] = '\0'; + else + strscpy(fw_str, "unknown", size); }
/* Parse the device information structure reported by the device and @@ -1314,7 +1316,6 @@ static int ucan_probe(struct usb_interface *intf, u8 in_ep_addr; u8 out_ep_addr; union ucan_ctl_payload *ctl_msg_buffer; - char firmware_str[sizeof(union ucan_ctl_payload) + 1];
udev = interface_to_usbdev(intf);
@@ -1527,17 +1528,6 @@ static int ucan_probe(struct usb_interface *intf, */ ucan_parse_device_info(up, &ctl_msg_buffer->cmd_get_device_info);
- /* just print some device information - if available */ - ret = ucan_device_request_in(up, UCAN_DEVICE_GET_FW_STRING, 0, - sizeof(union ucan_ctl_payload)); - if (ret > 0) { - /* copy string while ensuring zero termination */ - strscpy(firmware_str, up->ctl_msg_buffer->raw, - sizeof(union ucan_ctl_payload) + 1); - } else { - strcpy(firmware_str, "unknown"); - } - /* device is compatible, reset it */ ret = ucan_ctrl_command_out(up, UCAN_COMMAND_RESET, 0, 0); if (ret < 0) @@ -1555,7 +1545,10 @@ static int ucan_probe(struct usb_interface *intf,
/* initialisation complete, log device info */ netdev_info(up->netdev, "registered device\n"); - netdev_info(up->netdev, "firmware string: %s\n", firmware_str); + ucan_get_fw_str(up, up->ctl_msg_buffer->fw_str, + sizeof(up->ctl_msg_buffer->fw_str)); + netdev_info(up->netdev, "firmware string: %s\n", + up->ctl_msg_buffer->fw_str);
/* success */ return 0;
base-commit: 4003c9e78778e93188a09d6043a74f7154449d43