CVE-2023-3019: DMA Reentrancy Issue in QEMU e100e NIC Emulation Code Leads to Use-After-Free Error

Recently, researchers uncovered a critical vulnerability, dubbed CVE-2023-3019, in the QEMU (Quick EMUlator) e100e NIC emulation code. This vulnerability arises due to a DMA (Direct Memory Access) reentrancy issue that leads to a use-after-free error. If exploited, a privileged guest user can crash the QEMU process on the host, causing significant denial of service (DoS) consequences.

Description

QEMU is an open-source, widely-used emulator program that allows developers to create and manage virtual machines for various architectures, such as x86, MIPS, and ARM. The e100e NIC emulation code in QEMU is responsible for emulating the functionality of the e100e (Intel Ethernet Controller) inside the virtual machines. However, a flaw was found in its implementation.

The culprit behind this vulnerability is a DMA reentrancy issue, which arises when a DMA controller does not handle shared data structures properly, leading to memory corruption and potential use-after-free errors. In the case of CVE-2023-3019, the use-after-free error occurs in the e100e NIC emulation code of QEMU that manages memory for packet data.

Exploit Details

On analyzing the code in question, researchers found a logic flaw wherein DMA reentrancy was mishandled when the guest transmitted packets to the host. Precisely, the DMA engine did not differentiate between new packets and reentrant requests while processing transmitted packets.

Here's a code snippet illustrating the problematic implementation

static void
e100e_core_write_tx_descr(E100ECore *core, E100TXD *txd)
{
    dma_addr_t addr;

    addr = txd->buffer_addr & ~E100_TXD_CMD_DEXT;

    if (!(txd->cmd & E100_TXD_CMD_DEXT)) {
        /* descriptor extension not enabled */
        core->tx[rbd].buffer_addr = addr;
        core->tx[rbd].length = txd->length;
        core->tx[rbd].flags = txd->flags;
    }
}

The above code snippet does not account for the possibility of reentrant DMA requests and blindly handles transmitted packets without verifying their validity.

To successfully exploit this vulnerability, an attacker with privileged access to the guest virtual machine can carefully craft malicious packets and transmit them to the host. Consequently, the QEMU process running on the host would crash due to the use-after-free error, leading to a denial of service.

Original References

- Vulnerability Details of CVE-2023-3019
- QEMU official website

Mitigation

Fortunately, QEMU developers have already released a patch to address this issue. Users are strongly advised to update their QEMU installations to the latest version. The patch contains modifications to the e100e NIC emulation code which ensures proper handling of DMA reentrancy and prevention of use-after-free errors.

Conclusion

CVE-2023-3019 is a significant vulnerability that can have severe consequences if left unaddressed. This article underscores the importance of continuously updating and patching software to reduce the risk of exposure. Developers and administrators alike should ensure that their QEMU installations are up-to-date and diligently monitor security bulletins for future advisories.

Timeline

Published on: 07/24/2023 16:15:00 UTC
Last modified on: 08/31/2023 19:15:00 UTC