CVE ID:	CVE-2024-35944
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."
Test IDs:	None available
Cross References:	Common Vulnerability Exposure (CVE) ID: CVE-2024-35944 https://git.kernel.org/stable/c/130b0cd064874e0d0f58e18fb00e6f3993e90c74 https://git.kernel.org/stable/c/130b0cd064874e0d0f58e18fb00e6f3993e90c74 https://git.kernel.org/stable/c/19b070fefd0d024af3daa7329cbc0d00de5302ec https://git.kernel.org/stable/c/19b070fefd0d024af3daa7329cbc0d00de5302ec https://git.kernel.org/stable/c/491a1eb07c2bd8841d63cb5263455e185be5866f https://git.kernel.org/stable/c/491a1eb07c2bd8841d63cb5263455e185be5866f https://git.kernel.org/stable/c/ad78c5047dc4076d0b3c4fad4f42ffe9c86e8100 https://git.kernel.org/stable/c/ad78c5047dc4076d0b3c4fad4f42ffe9c86e8100 https://git.kernel.org/stable/c/dae70a57565686f16089737adb8ac64471570f73 https://git.kernel.org/stable/c/dae70a57565686f16089737adb8ac64471570f73 https://git.kernel.org/stable/c/e87bb99d2df6512d8ee37a5d63d2ca9a39a8c051 https://git.kernel.org/stable/c/e87bb99d2df6512d8ee37a5d63d2ca9a39a8c051 https://git.kernel.org/stable/c/f15eca95138b3d4ec17b63c3c1937b0aa0d3624b https://git.kernel.org/stable/c/f15eca95138b3d4ec17b63c3c1937b0aa0d3624b https://git.kernel.org/stable/c/feacd430b42bbfa9ab3ed9e4f38b86c43e348c75 https://git.kernel.org/stable/c/feacd430b42bbfa9ab3ed9e4f38b86c43e348c75