[PATCH net v4] nfc: nci: fix use of uninitialized memory in NFC-DEP general bytes

[Muhammad Bilal <meatuni001@gmail.com>]

nci_store_general_bytes_nfc_dep() derives the length of the NFC-DEP
general bytes by subtracting the fixed general-bytes offset from the
ATR length:

  atr_res_len - NFC_ATR_RES_GT_OFFSET   (poll, offset 15)
  atr_req_len - NFC_ATR_REQ_GT_OFFSET   (listen, offset 14)

It never checks that the ATR is at least that long. When a
RF_INTF_ACTIVATED_NTF reports an ATR shorter than the offset the
subtraction is negative; because min_t() casts its arguments to __u8
the negative value becomes large and is then capped at
NFC_ATR_RES_GB_MAXSIZE / NFC_ATR_REQ_GB_MAXSIZE. remote_gb_len is thus
set to up to 47/48 even though only atr_res_len/atr_req_len bytes of
the on-stack atr_res/atr_req buffer were copied from the packet, and
the following memcpy() reads the uninitialized remainder into
ndev->remote_gb.

Reject the notification with NCI_STATUS_RF_PROTOCOL_ERROR when the ATR
is shorter than the general-bytes offset, rather than silently
continuing. The return value is not decorative: in
nci_rf_intf_activated_ntf_packet(), a non-OK status here skips
nci_target_auto_activated(), is propagated as the completion status by
nci_req_complete(), and skips nfc_tm_activated(). Silently continuing
with remote_gb_len left at 0 would report the malformed activation as
a successful one with empty general bytes quietly substituted in,
rather than as the failure it is.

This bug has two independent points of origin. The POLL-mode
subtraction was introduced in commit 767f19ae698e ("NFC: Implement
NCI dep_link_up and dep_link_down"), which is where remote_gb and
remote_gb_len were first added. The LISTEN-mode subtraction did not
exist until commit a99903ec4566 ("NFC: NCI: Handle Target mode
activation"), which refactored the POLL-only code into the current
nci_store_general_bytes_nfc_dep() and added LISTEN-mode support fresh.
Both are tagged below.

Fixes: 767f19ae698e ("NFC: Implement NCI dep_link_up and dep_link_down")
Fixes: a99903ec4566 ("NFC: NCI: Handle Target mode activation")
Cc: stable@vger.kernel.org
Suggested-by: Lekë Hapçiu <snowwlake@icloud.com>
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
---
v4: Return NCI_STATUS_RF_PROTOCOL_ERROR instead of silently breaking
    out of the switch, matching the behavior independently proposed
    by Lekë Hapçiu. The break left remote_gb_len at 0 but still fell
    through to the function's final "return NCI_STATUS_OK", so a
    malformed ATR was reported up the stack as a successful
    activation instead of a failed one. Added a second Fixes tag:
    767f19ae698e is where the POLL-mode subtraction was first
    introduced in 2012, predating a99903ec4566 (2014), which only
    introduced the LISTEN-mode branch.
v3: Rebased onto current net.git for-next, requested by David
    Heidelberg. The function moved and gained an unconditional
    "remote_gb_len = 0" at entry (from commit 9c328f54741b, landed
    after v2 was posted), which made v2's explicit zeroing inside the
    short-ATR branch redundant, so this version drops it and only
    adds the missing length checks.
v2: Also zero remote_gb_len explicitly in the short-ATR branch so a
    stale value from a previous activation doesn't survive into the
    new session.

 net/nfc/nci/ntf.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/nfc/nci/ntf.c b/net/nfc/nci/ntf.c
index c96512b..c2352ea 100644
--- a/net/nfc/nci/ntf.c
+++ b/net/nfc/nci/ntf.c
@@ -631,6 +631,9 @@ static int nci_store_general_bytes_nfc_dep(struct nci_dev *ndev,
 	switch (ntf->activation_rf_tech_and_mode) {
 	case NCI_NFC_A_PASSIVE_POLL_MODE:
 	case NCI_NFC_F_PASSIVE_POLL_MODE:
+		if (ntf->activation_params.poll_nfc_dep.atr_res_len <
+		    NFC_ATR_RES_GT_OFFSET)
+			return NCI_STATUS_RF_PROTOCOL_ERROR;
 		ndev->remote_gb_len = min_t(__u8,
 			(ntf->activation_params.poll_nfc_dep.atr_res_len
 						- NFC_ATR_RES_GT_OFFSET),
@@ -643,6 +646,9 @@ static int nci_store_general_bytes_nfc_dep(struct nci_dev *ndev,
 
 	case NCI_NFC_A_PASSIVE_LISTEN_MODE:
 	case NCI_NFC_F_PASSIVE_LISTEN_MODE:
+		if (ntf->activation_params.listen_nfc_dep.atr_req_len <
+		    NFC_ATR_REQ_GT_OFFSET)
+			return NCI_STATUS_RF_PROTOCOL_ERROR;
 		ndev->remote_gb_len = min_t(__u8,
 			(ntf->activation_params.listen_nfc_dep.atr_req_len
 						- NFC_ATR_REQ_GT_OFFSET),
-- 
2.55.0