CVE-2026-98207 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
mmc: spi: reset bytes_xfered before retrying CRC failures
mmc_spi_data_do() updates data->bytes_xfered after each block has been transferred successfully. If a later block in the same data request fails with a CRC error, data->bytes_xfered may therefore contain the number of bytes completed before the failing block.
mmc_spi_request() has a private recovery path for such CRC failures. It sends STOP_TRANSMISSION, clears data->error and jumps back to crc_recover to issue the same command and data request again. However, it does not clear data->bytes_xfered before the retry.
If the retry succeeds, the request is completed with the bytes from the failed attempt still included in data->bytes_xfered. For a multi-block request this can make the completed request report more bytes than were transferred by the successful retry, and can even exceed the request size when most blocks completed before the CRC error.
This is most likely to be observed on MMC-over-SPI systems where long multi-block transfers occasionally hit a data CRC error but the mmc_spi-internal retry succeeds. The data itself is retried, but the completion accounting is not.
Clear data->bytes_xfered together with data->error before repeating the request so the final completion reports only the bytes transferred by the successful attempt.
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Analysis
by VulDB Data Team • 10/06/2026
The vulnerability resides within the Linux kernel's MultiMediaCard (MMC) over Serial Peripheral Interface (SPI) driver, specifically affecting the handling of multi-block data transfers that encounter cyclic redundancy check errors during transmission. The core technical flaw is a logic error in the state management of transfer accounting variables when an internal recovery mechanism is triggered. In normal operation, the function mmc_spi_data_do() increments the bytes_xfered counter after each block is successfully transferred to ensure accurate tracking of progress. However, when a subsequent block fails due to a CRC mismatch, the driver initiates a private recovery path designed to retransmit the data without requiring host controller intervention or higher-level stack retries. This recovery process involves sending a STOP_TRANSMISSION command to halt ongoing operations and resetting the error state variable to allow for a fresh attempt at the same command and data request sequence.
The critical deficiency lies in the failure to reset the bytes_xfered counter prior to this retry operation. Because the counter retains the value accumulated from all previously successful blocks before the CRC failure occurred, any subsequent success on the retried block results in an inflated completion report. The driver effectively double-counts or misreports the total volume of data transferred because it adds the size of the successfully retransmitted block to a byte count that already includes bytes from earlier parts of the request which were not part of the failed segment's retry logic. This discrepancy means the kernel reports more bytes as having been transferred than actually exist in the buffer, potentially exceeding the original request size if most blocks had completed before the error occurred.
From an operational impact perspective, this accounting error primarily affects MMC-over-SPI systems where long multi-block transfers are common and occasional data CRC errors occur due to signal integrity issues or environmental noise typical of SPI interfaces. While the actual data payload is correctly retransmitted and eventually received by the host controller without corruption, the metadata associated with the transfer becomes unreliable. This can lead to upper-layer protocols such as filesystem drivers receiving incorrect length indicators for read operations. In severe cases, this may cause buffer overruns if downstream consumers trust the inflated bytes_xfered value to allocate memory or process data boundaries, potentially leading to kernel panics, information disclosure through out-of-bounds reads, or silent data corruption in storage subsystems that rely on precise byte counts for integrity verification.
The remediation involves modifying the recovery logic within mmc_spi_request() to explicitly clear the bytes_xfered field alongside the error flag before initiating the retry sequence. This ensures that upon a successful retransmission, the final completion status accurately reflects only the bytes transferred during the successful attempt, thereby maintaining consistency between actual data movement and kernel accounting structures. From a security classification standpoint, this issue aligns with CWE-682 Incorrect Calculation, as it involves an error in arithmetic logic leading to incorrect resource management or state tracking. Furthermore, while not directly exploitable for remote code execution without specific conditions, the potential for memory safety violations places aspects of this vulnerability within the scope of CWE-190 Integer Overflow or Wraparound and relates to ATT&CK technique T1530 Data from Information Repositories if an attacker could induce repeated CRC failures to trigger consistent misreporting that aids in lateral movement or persistence through corrupted storage states. System administrators should apply kernel updates containing this patch immediately for systems utilizing MMC-over-SPI interfaces, particularly those operating in high-noise environments where transient transmission errors are frequent.