CVE-2024-35944 VMCI: Fix memcpy() run-time warning in dg_dispatch_as_host()
A kernel bug in the VMCI driver causes a runtime warning and potential crash when handling specific datagram payloads, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-35944?
CVE-2024-35944 is a medium-severity memory corruption vulnerability in Debian Debian Linux, published on 19 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
VMCI: Fix memcpy() run-time warning in dg_dispatch_as_host()
Syzkaller hit 'WARNING in dg_dispatch_as_host' bug.
memcpy: detected field-spanning write (size 56) of single field "&dg_info->msg" at drivers/misc/vmw_vmci/vmci_datagram.c:237 (size 24)
WARNING: CPU: 0 PID: 1555 at drivers/misc/vmw_vmci/vmci_datagram.c:237 dg_dispatch_as_host+0x88e/0xa60 drivers/misc/vmw_vmci/vmci_datagram.c:237
Some code commentry, based on my understanding:
544 #define VMCI_DG_SIZE(_dg) (VMCI_DG_HEADERSIZE + (size_t)(_dg)->payload_size) /// This is 24 + payload_size
memcpy(&dg_info->msg, dg, dg_size); Destination = dg_info->msg ---> this is a 24 byte structure(struct vmci_datagram) Source = dg --> this is a 24 byte structure (struct vmci_datagram) Size = dg_size = 24 + payload_size
{payload_size = 56-24 =32} -- Syzkaller managed to set payload_size to 32.
35 struct delayed_datagram_info { 36 struct datagram_entry *entry; 37 struct work_struct work; 38 bool in_dg_host_queue; 39 /* msg and msg_payload must be together. */ 40 struct vmci_datagram msg; 41 u8 msg_payload[]; 42 };
So those extra bytes of payload are copied into msg_payload[], a run time warning is seen while fuzzing with Syzkaller.
One possible way to fix the warning is to split the memcpy() into two parts -- one -- direct assignment of msg and second taking care of payload.
Gustavo quoted: "Under FORTIFY_SOURCE we should not copy data across multiple members in a structure."
Which versions are affected by CVE-2024-35944?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2024-35944?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2024-35944 being exploited?
There is no known exploitation of CVE-2024-35944 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as BELL-CVE-2024-35944, DEBIAN-CVE-2024-35944, GHSA-g37w-wjp2-mp83, UBUNTU-CVE-2024-35944.