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Commit 03aad851 authored by Hui Peng's avatar Hui Peng Committed by Android Build Coastguard Worker
Browse files

Fix an integer underflow in build_read_multi_rsp 

When p_buf->len is mtu - 1 and p_cmd->multi_req.variable_len
evaluates to true, integer underflow is triggered
in the following line, resulting OOB access.

```
 len = p_rsp->attr_value.len - (total_len - mtu);
```

Bug: 273874525
Test: manual
Ignore-AOSP-First: security
Tag: #security
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:85f4d53c7bf90b806639a3a302f0007ffb3b9f23)
Merged-In: Ia60dd829ff9152c083de1f4c1265bb3ad595dcc4
Change-Id: Ia60dd829ff9152c083de1f4c1265bb3ad595dcc4
parent dfdb94d5

system/stack/gatt/gatt_sr.cc

+17 −15
Original line number Diff line number Diff line
@@ -21,6 +21,7 @@ 
 *  this file contains the GATT server functions

 *

 ******************************************************************************/

#include <algorithm>

#include <string.h>



#include "bt_target.h"
@@ -179,37 +180,38 @@ static void build_read_multi_rsp(tGATT_SR_CMD* p_cmd, uint16_t mtu) { 
    }



    if (p_rsp != NULL) {

      total_len = (p_buf->len + p_rsp->attr_value.len);

      total_len = p_buf->len;

      if (p_cmd->multi_req.variable_len) {

        total_len += 2;

      }



      if (total_len > mtu) {

        /* just send the partial response for the overflow case */

        len = p_rsp->attr_value.len - (total_len - mtu);

        VLOG(1) << "Buffer space not enough for this data item, skipping";

        break;

      }



      len = std::min((size_t) p_rsp->attr_value.len, mtu - total_len);



      if (len == 0) {

        VLOG(1) << "Buffer space not enough for this data item, skipping";

        break;

      }



      if (len < p_rsp->attr_value.len) {

        is_overflow = true;

        VLOG(1) << StringPrintf(

            "multi read overflow available len=%zu val_len=%d", len,

            p_rsp->attr_value.len);

      } else {

        len = p_rsp->attr_value.len;

      }



      if (p_cmd->multi_req.variable_len) {

        UINT16_TO_STREAM(p, len);

        UINT16_TO_STREAM(p, (uint16_t) len);

        p_buf->len += 2;

      }



      if (p_rsp->attr_value.handle == p_cmd->multi_req.handles[ii]) {

        // check for possible integer overflow

        if (p_buf->len + len <= UINT16_MAX) {

          memcpy(p, p_rsp->attr_value.value, len);

          if (!is_overflow) p += len;

          p_buf->len += len;

        } else {

          p_cmd->status = GATT_NOT_FOUND;

          break;

        }

        ARRAY_TO_STREAM(p, p_rsp->attr_value.value, (uint16_t) len);

        p_buf->len += (uint16_t) len;

      } else {

        p_cmd->status = GATT_NOT_FOUND;

        break;