Input: ims-pcu - fix heap-buffer-overflow in ims_pcu_process_data()

The `ims_pcu_process_data()` processes incoming URB data byte by byte.
However, it fails to check if the `read_pos` index exceeds
IMS_PCU_BUF_SIZE.

If a malicious USB device sends a packet larger than IMS_PCU_BUF_SIZE,
`read_pos` will increment indefinitely. Moreover, since `read_pos` is
located immediately after `read_buf`, the attacker can overwrite
`read_pos` itself to arbitrarily control the index.

This manipulated `read_pos` is subsequently used in
`ims_pcu_handle_response()` to copy data into `cmd_buf`, leading to a
heap buffer overflow.

Specifically, an attacker can overwrite the `cmd_done.wait.head` located
at offset 136 relative to `cmd_buf` in the `ims_pcu_handle_response()`.
Consequently, when the driver calls `complete(&pcu->cmd_done)`, it
triggers a control flow hijack by using the manipulated pointer.

Fix this by adding a bounds check for `read_pos` before writing to
`read_buf`. If the packet is too long, discard it, log a warning,
and reset the parser state.

Fixes: 628329d524743 ("Input: add IMS Passenger Control Unit driver")
Co-developed-by: Sanghoon Choi <csh0052@gmail.com>
Signed-off-by: Sanghoon Choi <csh0052@gmail.com>
Signed-off-by: Seungjin Bae <eeodqql09@gmail.com>
Link: https://patch.msgid.link/20251221211442.841549-2-eeodqql09@gmail.com
[dtor: factor out resetting packet state, reset checksum as well]
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

diff --git a/drivers/input/misc/ims-pcu.c b/drivers/input/misc/ims-pcu.c
index f69de9762c4e34eb87ed26e6e397d15073912c4b..4c022a36dbe844ec340d05f52555e0649dc45c64 100644 (file)
--- a/drivers/input/misc/ims-pcu.c
+++ b/drivers/input/misc/ims-pcu.c
@@ -438,6 +438,14 @@ static void ims_pcu_handle_response(struct ims_pcu *pcu)
        }
 }
 
+static void ims_pcu_reset_packet(struct ims_pcu *pcu)
+{
+       pcu->have_stx = true;
+       pcu->have_dle = false;
+       pcu->read_pos = 0;
+       pcu->check_sum = 0;
+}
+
 static void ims_pcu_process_data(struct ims_pcu *pcu, struct urb *urb)
 {
        int i;
@@ -450,6 +458,14 @@ static void ims_pcu_process_data(struct ims_pcu *pcu, struct urb *urb)
                        continue;
 
                if (pcu->have_dle) {
+                       if (pcu->read_pos >= IMS_PCU_BUF_SIZE) {
+                               dev_warn(pcu->dev,
+                                        "Packet too long (%d bytes), discarding\n",
+                                        pcu->read_pos);
+                               ims_pcu_reset_packet(pcu);
+                               continue;
+                       }
+
                        pcu->have_dle = false;
                        pcu->read_buf[pcu->read_pos++] = data;
                        pcu->check_sum += data;
@@ -462,10 +478,8 @@ static void ims_pcu_process_data(struct ims_pcu *pcu, struct urb *urb)
                                dev_warn(pcu->dev,
                                         "Unexpected STX at byte %d, discarding old data\n",
                                         pcu->read_pos);
+                       ims_pcu_reset_packet(pcu);
                        pcu->have_stx = true;
-                       pcu->have_dle = false;
-                       pcu->read_pos = 0;
-                       pcu->check_sum = 0;
                        break;
 
                case IMS_PCU_PROTOCOL_DLE:
@@ -485,12 +499,18 @@ static void ims_pcu_process_data(struct ims_pcu *pcu, struct urb *urb)
                                ims_pcu_handle_response(pcu);
                        }
 
-                       pcu->have_stx = false;
-                       pcu->have_dle = false;
-                       pcu->read_pos = 0;
+                       ims_pcu_reset_packet(pcu);
                        break;
 
                default:
+                       if (pcu->read_pos >= IMS_PCU_BUF_SIZE) {
+                               dev_warn(pcu->dev,
+                                        "Packet too long (%d bytes), discarding\n",
+                                        pcu->read_pos);
+                               ims_pcu_reset_packet(pcu);
+                               continue;
+                       }
+
                        pcu->read_buf[pcu->read_pos++] = data;
                        pcu->check_sum += data;
                        break;