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Fix integer overflow-prone offset+len bounds checks in NVM read handlers #319

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Fix integer overflow-prone offset+len bounds checks in NVM read handlers #319

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10 changes: 6 additions & 4 deletions src/wh_nvm_flash.c
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Original file line number Diff line number Diff line change
Expand Up @@ -500,7 +500,8 @@ static int nfPartition_CheckDataRange(whNvmFlashContext* context,
return WH_ERROR_BADARGS;
}

if (byte_offset + byte_count > maxOffset) {
/* Use overflow-safe comparison */
if (byte_offset > maxOffset || byte_count > maxOffset - byte_offset) {
return WH_ERROR_BADARGS;
}

Expand Down Expand Up @@ -665,13 +666,14 @@ static int nfObject_ReadDataBytes(whNvmFlashContext* context, int partition,
start = context->directory.objects[object_index].state.start;
startOffset = nfPartition_DataOffset(context, partition) + start;

/* object bounds checks, do both to avoid integer overflow checks */
/* object bounds checks, use overflow-safe comparison */
if (byte_offset >=
(context->directory.objects[object_index].metadata.len)) {
return WH_ERROR_BADARGS;
}
if ((byte_offset + byte_count) >
(context->directory.objects[object_index].metadata.len)) {
if (byte_count >
(uint32_t)(context->directory.objects[object_index].metadata.len) -
byte_offset) {
return WH_ERROR_BADARGS;
}

Expand Down
9 changes: 5 additions & 4 deletions src/wh_server_nvm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -67,8 +67,8 @@ static int _HandleNvmRead(whServerContext* server, uint8_t* out_data,
if (offset >= meta.len)
return WH_ERROR_BADARGS;

/* Clamp length to object size */
if ((offset + len) > meta.len) {
/* Clamp length to object size, use overflow-safe comparison */
if (len > meta.len - offset) {
len = meta.len - offset;
}

Expand Down Expand Up @@ -427,8 +427,9 @@ int wh_Server_HandleNvmRequest(whServerContext* server,

if (rc == 0) {
read_len = req.data_len;
/* Clamp length to object size */
if ((req.offset + read_len) > meta.len) {
/* Clamp length to object size, use overflow-safe
* comparison */
if (read_len > meta.len - req.offset) {
read_len = meta.len - req.offset;
}
}
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23 changes: 23 additions & 0 deletions test/wh_test_clientserver.c
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Original file line number Diff line number Diff line change
Expand Up @@ -562,6 +562,29 @@ static int _testOutOfBoundsNvmReads(whClientContext* client,
wh_Client_NvmReadResponse(client, &server_rc, &len, buffer));
WH_TEST_ASSERT_RETURN(server_rc == WH_ERROR_BADARGS);

/* Test with large offset (UINT16_MAX), should fail since offset >=
* meta.len. Regression test for integer overflow safety in the
* offset+len check */
off = UINT16_MAX;
len = 1;
Comment on lines +565 to +569
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Copilot AI Mar 20, 2026

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The new “large offset (UINT16_MAX)” case will fail the earlier offset >= meta.len guard regardless of whether the old offset + len overflow-prone check was present, so it doesn’t actually exercise the regression you describe. To validate the overflow-safe clamp, consider adding a case where offset < meta.len but offset + len would wrap a 16-bit whNvmSize (e.g., with a near-UINT16_MAX object length via DMA path or a backend helper) and assert the read is rejected/clamped correctly.

Suggested change
/* Test with large offset (UINT16_MAX), should fail since offset >=
* meta.len. Regression test for integer overflow safety in the
* offset+len check */
off = UINT16_MAX;
len = 1;
/* Test with offset < meta.len but len large enough that a naive
* 16-bit (whNvmSize) offset+len computation would wrap. Regression
* test for integer overflow safety in the offset+len check. */
off = 1;
len = UINT16_MAX;

Copilot uses AI. Check for mistakes.
WH_TEST_RETURN_ON_FAIL(wh_Client_NvmReadRequest(client, id, off, len));
WH_TEST_RETURN_ON_FAIL(wh_Server_HandleRequestMessage(server));
WH_TEST_RETURN_ON_FAIL(
wh_Client_NvmReadResponse(client, &server_rc, &len, buffer));
WH_TEST_ASSERT_RETURN(server_rc == WH_ERROR_BADARGS);

/* Test clamping with offset at midpoint and len exceeding remaining object
* size. Verifies the overflow-safe comparison (len > meta.len - offset)
* correctly clamps when offset + len would exceed meta.len */
off = meta.len / 2;
len = meta.len;
WH_TEST_RETURN_ON_FAIL(wh_Client_NvmReadRequest(client, id, off, len));
WH_TEST_RETURN_ON_FAIL(wh_Server_HandleRequestMessage(server));
WH_TEST_RETURN_ON_FAIL(
wh_Client_NvmReadResponse(client, &server_rc, &len, buffer));
WH_TEST_ASSERT_RETURN(server_rc == WH_ERROR_OK);
WH_TEST_ASSERT_RETURN(len == meta.len - meta.len / 2);

return WH_ERROR_OK;
}

Expand Down
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