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."

kernel.org https://git.kernel.org/stable/c/130b0cd064874e0d0f58e18fb00e6f3993e90c74 [No types assigned]

kernel.org https://git.kernel.org/stable/c/19b070fefd0d024af3daa7329cbc0d00de5302ec [No types assigned]

kernel.org https://git.kernel.org/stable/c/491a1eb07c2bd8841d63cb5263455e185be5866f [No types assigned]

kernel.org https://git.kernel.org/stable/c/ad78c5047dc4076d0b3c4fad4f42ffe9c86e8100 [No types assigned]

kernel.org https://git.kernel.org/stable/c/dae70a57565686f16089737adb8ac64471570f73 [No types assigned]

kernel.org https://git.kernel.org/stable/c/e87bb99d2df6512d8ee37a5d63d2ca9a39a8c051 [No types assigned]

kernel.org https://git.kernel.org/stable/c/f15eca95138b3d4ec17b63c3c1937b0aa0d3624b [No types assigned]

kernel.org https://git.kernel.org/stable/c/feacd430b42bbfa9ab3ed9e4f38b86c43e348c75 [No types assigned]