[PATCH] nfc: pn533: validate response length before parsing DEP ATR_RES

[hyunjungg <hj351016@gmail.com>]

From: Hyunjung Ko <hj351016@gmail.com>

pn533_poll_dep_complete() and pn533_in_dep_link_up_complete() cast
resp->data to a struct pn533_cmd_jump_dep_response and read its fixed
17-byte header (status, tg, nfcid3t[10], didt, bst, brt, to, ppt)
without first checking that resp->len covers that header.

On a short or truncated response the handlers read bytes beyond the
received frame:

  - rsp->status is dereferenced with no minimum-length check;
  - for a success status, memcpy(nfc_target.nfcid1, rsp->nfcid3t, 10)
    copies 10 bytes from offset 2, so for resp->len < 12 it reads past
    the valid response data. Those bytes are then handed to userspace
    via nfc_targets_found() (netlink), which can disclose stale buffer
    contents.

target_gt_len = resp->len - 17 additionally underflows (it is u8) when
resp->len < 17. That path is mitigated downstream --
nfc_set_remote_general_bytes() -> nfc_llcp_set_remote_gb() rejects the
resulting out-of-range length -- so the subtraction does not by itself
over-read rsp->gt[]; the fixed-field reads above are unguarded
regardless.

A valid ATR_RES always carries the full 17-byte fixed header (the
general bytes, if present, start at offset 17), so reject any response
shorter than sizeof(*rsp) before parsing it. pn533_rf_complete()-style
handlers in this file already length-check resp->len before use (e.g.
the ATR_REQ_GB_OFFSET check in pn533_init_target_complete()).

Found by code review; not reproduced.

Signed-off-by: Hyunjung Ko <hj351016@gmail.com>
---
 drivers/nfc/pn533/pn533.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/nfc/pn533/pn533.c b/drivers/nfc/pn533/pn533.c
--- a/drivers/nfc/pn533/pn533.c
+++ b/drivers/nfc/pn533/pn533.c
@@ -1309,7 +1309,12 @@ static int pn533_poll_dep_complete(struct pn533 *dev, void *arg,
 	memset(&nfc_target, 0, sizeof(struct nfc_target));

 	rsp = (struct pn533_cmd_jump_dep_response *)resp->data;

+	if (resp->len < sizeof(*rsp)) {
+		rc = -EINVAL;
+		goto error;
+	}
+
 	rc = rsp->status & PN533_CMD_RET_MASK;
 	if (rc != PN533_CMD_RET_SUCCESS) {
 		/* Not target found, turn radio off */
@@ -1929,7 +1929,12 @@ static int pn533_in_dep_link_up_complete(struct pn533 *dev, void *arg,
 	}

 	rsp = (struct pn533_cmd_jump_dep_response *)resp->data;

+	if (resp->len < sizeof(*rsp)) {
+		rc = -EINVAL;
+		goto error;
+	}
+
 	rc = rsp->status & PN533_CMD_RET_MASK;
 	if (rc != PN533_CMD_RET_SUCCESS) {
 		nfc_err(dev->dev,