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

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: 4ab8c18d4d67 ("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>

0 files changed, 0 insertions, 0 deletions