linux-kernel - [PATCH AUTOSEL 5.10 03/31] VMCI: Fix memcpy() run-time warning in dg_dispatch_as

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Date: Fri, 29 Mar 2024 08:48:20 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>,
	syzkaller <syzkaller@...glegroups.com>,
	Vegard Nossum <vegard.nossum@...cle.com>,
	"Gustavo A . R . Silva" <gustavoars@...nel.org>,
	Kees Cook <keescook@...omium.org>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Sasha Levin <sashal@...nel.org>,
	bryantan@...are.com,
	vdasa@...are.com,
	gregkh@...uxfoundation.org
Subject: [PATCH AUTOSEL 5.10 03/31] VMCI: Fix memcpy() run-time warning in dg_dispatch_as_host()

From: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.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@...glegroups.com>
Suggested-by: Vegard Nossum <vegard.nossum@...cle.com>
Suggested-by: Gustavo A. R. Silva <gustavoars@...nel.org>
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>
Reviewed-by: Kees Cook <keescook@...omium.org>
Reviewed-by: Dan Carpenter <dan.carpenter@...aro.org>
Link: https://lore.kernel.org/r/20240105164001.2129796-2-harshit.m.mogalapalli@oracle.com
Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Sasha Levin <sashal@...nel.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 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);
-- 
2.43.0