Overview
About vulnerability
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.”
Details
- Affected product:
- AlmaLinux 9.2 ESU , CentOS 6 ELS , CentOS 7 ELS , CentOS 8.4 ELS , CentOS 8.5 ELS , CentOS Stream 8 ELS , CloudLinux 6 ELS , CloudLinux 7 ELS , Oracle Linux 6 ELS , Oracle Linux 7 ELS , RHEL 7 ELS , Ubuntu 16.04 ELS , Ubuntu 18.04 ELS
- Affected packages:
- linux @ 4.4.0 (+15 more)
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.”