usb: typec: tcpm: Validate SVID index in svdm_consume_modes()

commit 7b681dd upstream.

In svdm_consume_modes(), the SVID value is read from pmdata->svids using
pmdata->svid_index as an array index without bounds validation:

    paltmode->svid = pmdata->svids[pmdata->svid_index];

If pmdata->svid_index is driven beyond SVID_DISCOVERY_MAX (16), it results
in an out-of-bounds read of the pmdata->svids array. Because pd_mode_data
is embedded inside struct tcpm_port, indexing past svids reads into
adjacent fields. In particular:
- At index 16, it reads the altmodes count.
- At index 18 and beyond, it reads into altmode_desc[], which contains
  partner-supplied SVDM Discovery Modes VDOs.

By injecting a chosen SVID into altmode_desc[0].vdo and driving svid_index
to 20, the partner can force paltmode->svid to be loaded with an arbitrary,
partner- chosen SVID, which is then registered via
typec_partner_register_altmode().

Fix this by validating that pmdata->svid_index is non-negative and strictly
less than pmdata->nsvids before accessing the pmdata->svids array inside
svdm_consume_modes().

Assisted-by: Antigravity:gemini-3.5-flash
Fixes: 4ab8c18 ("usb: typec: Register a device for every mode")
Cc: stable <stable@kernel.org>
Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
Reviewed-by: RD Babiera <rdbabiera@google.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://patch.msgid.link/20260622220803.305750-1-badhri@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Badhri Jagan Sridharan

drivers/usb/typec/tcpm/tcpm.c

@@ -1555,6 +1555,11 @@ static void svdm_consume_modes(struct tcpm_port *port, const u32 *p, int cnt)
 		return;
 	}
 
+	if (pmdata->svid_index < 0 || pmdata->svid_index >= pmdata->nsvids) {
+		tcpm_log(port, "Invalid SVID index %d", pmdata->svid_index);
+		return;
+	}
+
 	for (i = 1; i < cnt; i++) {
 		paltmode = &pmdata->altmode_desc[pmdata->altmodes];
 		memset(paltmode, 0, sizeof(*paltmode));