Patch "VMCI: Fix memcpy() run-time warning in dg_dispatch_as_host()" has been added to the 6.8-stable tree

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This is a note to let you know that I've just added the patch titled

    VMCI: Fix memcpy() run-time warning in dg_dispatch_as_host()

to the 6.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     vmci-fix-memcpy-run-time-warning-in-dg_dispatch_as_h.patch
and it can be found in the queue-6.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 7279cf06725cf61c6e27be5556c315258b08dcbf
Author: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>
Date:   Fri Jan 5 08:40:00 2024 -0800

    VMCI: Fix memcpy() run-time warning in dg_dispatch_as_host()
    
    [ 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@xxxxxxxxxxxxxxxx>
    Suggested-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
    Suggested-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
    Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>
    Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
    Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
    Reviewed-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240105164001.2129796-2-harshit.m.mogalapalli@xxxxxxxxxx
    Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/misc/vmw_vmci/vmci_datagram.c b/drivers/misc/vmw_vmci/vmci_datagram.c
index f50d22882476f..d1d8224c8800c 100644
--- a/drivers/misc/vmw_vmci/vmci_datagram.c
+++ b/drivers/misc/vmw_vmci/vmci_datagram.c
@@ -234,7 +234,8 @@ 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);




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