From: Harshit Mogalapalli harshit.m.mogalapalli@oracle.com
[ Upstream commit 19b070fefd0d024af3daa7329cbc0d00de5302ec ]
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."
Reported-by: syzkaller syzkaller@googlegroups.com Suggested-by: Vegard Nossum vegard.nossum@oracle.com Suggested-by: Gustavo A. R. Silva gustavoars@kernel.org Signed-off-by: Harshit Mogalapalli harshit.m.mogalapalli@oracle.com Reviewed-by: Gustavo A. R. Silva gustavoars@kernel.org Reviewed-by: Kees Cook keescook@chromium.org Reviewed-by: Dan Carpenter dan.carpenter@linaro.org Link: https://lore.kernel.org/r/20240105164001.2129796-2-harshit.m.mogalapalli@ora... Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/misc/vmw_vmci/vmci_datagram.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/misc/vmw_vmci/vmci_datagram.c b/drivers/misc/vmw_vmci/vmci_datagram.c index 8a4b6bbe1beed..275542e8b2ad9 100644 --- a/drivers/misc/vmw_vmci/vmci_datagram.c +++ b/drivers/misc/vmw_vmci/vmci_datagram.c @@ -242,7 +242,8 @@ static int dg_dispatch_as_host(u32 context_id, struct vmci_datagram *dg)
dg_info->in_dg_host_queue = true; dg_info->entry = dst_entry; - memcpy(&dg_info->msg, dg, dg_size); + dg_info->msg = *dg; + memcpy(&dg_info->msg_payload, dg + 1, dg->payload_size);
INIT_WORK(&dg_info->work, dg_delayed_dispatch); schedule_work(&dg_info->work);