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Date: Mon, 1 Jan 2024 05:08:28 -0800
From: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
To: linux-hardening@...r.kernel.org, keescook@...omium.org,
gustavoars@...nel.org, Bryan Tan <bryantan@...are.com>,
Vishnu Dasa <vdasa@...are.com>,
VMware PV-Drivers Reviewers <pv-drivers@...are.com>,
Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org
Cc: vegard.nossum@...cle.com, darren.kenny@...cle.com,
harshit.m.mogalapalli@...cle.com,
syzkaller <syzkaller@...glegroups.com>
Subject: [RFC PATCH] VMCI: Silence memcpy() run-time false positive warning
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[], so there
is no bug, but a run time warning is seen while fuzzing with Syzkaller.
One possible way to silence the warning is to split the memcpy() into
two parts -- one -- copying the msg and second taking care of payload.
Reported-by: syzkaller <syzkaller@...glegroups.com>
Suggested-by: Vegard Nossum <vegard.nossum@...cle.com>
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
---
This patch is only tested with the C reproducer, not any testing
specific to driver is done.
---
drivers/misc/vmw_vmci/vmci_datagram.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/misc/vmw_vmci/vmci_datagram.c b/drivers/misc/vmw_vmci/vmci_datagram.c
index f50d22882476..b43661590f56 100644
--- a/drivers/misc/vmw_vmci/vmci_datagram.c
+++ b/drivers/misc/vmw_vmci/vmci_datagram.c
@@ -216,6 +216,7 @@ static int dg_dispatch_as_host(u32 context_id, struct vmci_datagram *dg)
if (dst_entry->run_delayed ||
dg->src.context == VMCI_HOST_CONTEXT_ID) {
struct delayed_datagram_info *dg_info;
+ size_t payload_size = dg_size - VMCI_DG_HEADERSIZE;
if (atomic_add_return(1, &delayed_dg_host_queue_size)
== VMCI_MAX_DELAYED_DG_HOST_QUEUE_SIZE) {
@@ -234,7 +235,8 @@ 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);
+ memcpy(&dg_info->msg, dg, VMCI_DG_HEADERSIZE);
+ memcpy(&dg_info->msg_payload, dg + 1, payload_size);
INIT_WORK(&dg_info->work, dg_delayed_dispatch);
schedule_work(&dg_info->work);
--
2.42.0
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