[PATCH] usb: typec: ucsi: ccg: reject firmware images without a ':' record header

[Greg Kroah-Hartman]

do_flash() locates the first .cyacd record with

	p = strnchr(fw->data, fw->size, ':');
	while (p < eof) {
		s = strnchr(p + 1, eof - p - 1, ':');
		...
	}

If the firmware image contains no ':' byte,  strnchr() returns NULL.
NULL compares less than the valid kernel pointer eof, so the loop body
runs and strnchr() is called with p + 1 == (void *)1 and a length of
roughly (unsigned long)eof, causing a wonderful crash.

The not_signed_fw fallthrough earlier in do_flash() and the chip-state
branches in ccg_fw_update_needed() allow an unsigned blob to reach this
loop, so a root user who can place a crafted file under /lib/firmware
and write the do_flash sysfs attribute can trigger the oops.

Bail out with -EINVAL when the initial strnchr() returns NULL.

Assisted-by: gkh_clanker_t1000
Cc: stable <stable@xxxxxxxxxx>
Cc: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/usb/typec/ucsi/ucsi_ccg.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/usb/typec/ucsi/ucsi_ccg.c b/drivers/usb/typec/ucsi/ucsi_ccg.c
index 199799b319c2..4463c1ae96bd 100644
--- a/drivers/usb/typec/ucsi/ucsi_ccg.c
+++ b/drivers/usb/typec/ucsi/ucsi_ccg.c
@@ -1243,6 +1243,11 @@ static int do_flash(struct ucsi_ccg *uc, enum enum_flash_mode mode)
 	 *****************************************************************/
 
 	p = strnchr(fw->data, fw->size, ':');
+	if (!p) {
+		dev_err(dev, "Bad FW format: no ':' record header found\n");
+		err = -EINVAL;
+		goto release_mem;
+	}
 	while (p < eof) {
 		s = strnchr(p + 1, eof - p - 1, ':');
 
-- 
2.54.0