tools/net/ynl: fix cli.py --subscribe feature

Execution of command:
./tools/net/ynl/cli.py --spec Documentation/netlink/specs/dpll.yaml /

	--subscribe "monitor" --sleep 10
fails with:
Traceback (most recent call last):
  File "/root/arek/linux-dpll/./tools/net/ynl/cli.py", line 114, in <module>
    main()
  File "/root/arek/linux-dpll/./tools/net/ynl/cli.py", line 109, in main
    ynl.check_ntf()
  File "/root/arek/linux-dpll/tools/net/ynl/lib/ynl.py", line 924, in check_ntf
    op = self.rsp_by_value[nl_msg.cmd()]

KeyError: 19

The key value of 19 returned from nl_msg.cmd() is a received message header's nl_type, which is the id value of generic netlink family being addressed in the OS on subscribing. It is wrong to use it for decoding the notification. Expected notification message on dpll subsystem is DPLL_CMD_PIN_CHANGE_NTF=13, seems at that point only available as first byte of RAW message payload, use it to target correct op and allow further parsing.

Fixes "0a966d606c68" ("tools/net/ynl: Fix extack decoding for directional ops")

Signed-off-by Arkadiusz Kubalewski <[email protected]>

---
 tools/net/ynl/lib/ynl.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

tools/net/ynl/lib/ynl.py +0 -0

index d42c1d605969..192d6c150303 100644

tools/net/ynl/lib/ynl.py +0 -0

                 decoded = self.nlproto.decode(self, nl_msg, op)
                 if decoded.cmd() not in self.async_msg_ids:
                     print("Unexpected msg id done while checking for ntf", decoded)

From: Donald Hunter <[email protected]>
Sent: Friday, August 23, 2024 12:40 PM

Quoted 37 lines · Arkadiusz Kubalewski

Execution of command:
./tools/net/ynl/cli.py --spec Documentation/netlink/specs/dpll.yaml /

	--subscribe "monitor" --sleep 10
fails with:
Traceback (most recent call last):
  File "/root/arek/linux-dpll/./tools/net/ynl/cli.py", line 114, in <module>
    main()
  File "/root/arek/linux-dpll/./tools/net/ynl/cli.py", line 109, in main
    ynl.check_ntf()
  File "/root/arek/linux-dpll/tools/net/ynl/lib/ynl.py", line 924, in
check_ntf
    op = self.rsp_by_value[nl_msg.cmd()]

KeyError: 19

The key value of 19 returned from nl_msg.cmd() is a received message header's nl_type, which is the id value of generic netlink family being addressed in the OS on subscribing. It is wrong to use it for decoding the notification. Expected notification message on dpll subsystem is DPLL_CMD_PIN_CHANGE_NTF=13, seems at that point only available as first byte of RAW message payload, use it to target correct op and allow further parsing.

Fixes: "0a966d606c68" ("tools/net/ynl: Fix extack decoding for directional ops")

Signed-off-by Arkadiusz Kubalewski <[email protected]>

---
 tools/net/ynl/lib/ynl.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

tools/net/ynl/lib/ynl.py +0 -0

index d42c1d605969..192d6c150303 100644
@@ -921,7 +921,7 @@ class YnlFamily(SpecFamily):
                     print("Netlink done while checking for ntf!?")
                     continue
 

tools/net/ynl/lib/ynl.py class YnlFamily(SpecFamily): · line 924

Quoted 2 lines

tools/net/ynl/lib/ynl.py +1 -1

-                op = self.rsp_by_value[nl_msg.cmd()]
+                op = self.rsp_by_value[nl_msg.raw[0]]

I don't think that is the right fix. It would break notifications for raw netlink messages. The point of NlMsg.cmd() is to abstract away where the op id comes from. GenlMsg.cmd() returns the value unpacked from raw[0].

The problem is that we are trying to look up the op before calling nlproto.decode(...) but it wants to know the op to check if it has a fixed header.

I think the fix would be to change NetlinkProtocol.decode() to perform the op lookup, if necessary, after it has called self._decode() to unpack the GenlMsg.

How about changing NetlinkProtocol.decode() to be:

def decode(self, ynl, nl_msg, op, ops_by_value):
msg = self._decode(nl_msg)
if op is None:

       op = ops_by_value[msg.cmd()]

...

The main loop can call it like this:

nlproto.decode(self, nl_msg, op, self.rsp_by_value)

and check_ntf() can call it like this:

nlproto.decode(self, nl_msg, None, self.rsp_by_value)

Quoted 4 lines

decoded = self.nlproto.decode(self, nl_msg, op) if decoded.cmd() not in self.async_msg_ids:
print("Unexpected msg id done while checking for ntf",
decoded)

Quoted 23 lines

The problem is that we are trying to look up the op before calling nlproto.decode(...) but it wants to know the op to check if it has a fixed header.

I think the fix would be to change NetlinkProtocol.decode() to perform the op lookup, if necessary, after it has called self._decode() to unpack the GenlMsg.

How about changing NetlinkProtocol.decode() to be:

def decode(self, ynl, nl_msg, op, ops_by_value):
msg = self._decode(nl_msg)
if op is None:

       op = ops_by_value[msg.cmd()]

...

The main loop can call it like this:

nlproto.decode(self, nl_msg, op, self.rsp_by_value)

and check_ntf() can call it like this:

Quoted 2 lines

nlproto.decode(self, nl_msg, None, self.rsp_by_value)

Yes, again, this seems much better, I will prepare new patch and send the non-RFC version soon.

Thanks for your help!
Arkadiusz

From: Donald Hunter <[email protected]>
Sent: Friday, August 23, 2024 11:23 PM

Quoted 23 lines · Arkadiusz

Quoted 23 lines

The problem is that we are trying to look up the op before calling nlproto.decode(...) but it wants to know the op to check if it has a fixed header.

I think the fix would be to change NetlinkProtocol.decode() to perform the op lookup, if necessary, after it has called self._decode() to unpack the GenlMsg.

How about changing NetlinkProtocol.decode() to be:

def decode(self, ynl, nl_msg, op, ops_by_value):
msg = self._decode(nl_msg)
if op is None:

       op = ops_by_value[msg.cmd()]

...

The main loop can call it like this:

nlproto.decode(self, nl_msg, op, self.rsp_by_value)

and check_ntf() can call it like this:

Quoted 8 lines

Quoted 2 lines

nlproto.decode(self, nl_msg, None, self.rsp_by_value)

Yes, again, this seems much better, I will prepare new patch and send the non-RFC version soon.

Thanks for your help!
Arkadiusz

I tried the changes locally to check it would work and ended up with the following patch. Can you verify that it fixes the issue you had?

tools/net/ynl/lib/ynl.py +4 -3

index d42c1d605969..311542a8aa24 100644
@@ -386,8 +386,10 @@ class NetlinkProtocol:
    def _decode(self, nl_msg):
        return nl_msg
 
-    def decode(self, ynl, nl_msg, op):
+    def decode(self, ynl, nl_msg, op, ops_by_value):
        msg = self._decode(nl_msg)
+        if op is None:
+            op = ops_by_value[msg.cmd()]
        fixed_header_size = ynl._struct_size(op.fixed_header)
        msg.raw_attrs = NlAttrs(msg.raw, fixed_header_size)
        return msg

@@ -921,8 +923,7 @@ class YnlFamily(SpecFamily):
                    print("Netlink done while checking for ntf!?")
                    continue
 
-                op = self.rsp_by_value[nl_msg.cmd()]
-                decoded = self.nlproto.decode(self, nl_msg, op)
+                decoded = self.nlproto.decode(self, nl_msg, None,
 self.rsp_by_value)
                if decoded.cmd() not in self.async_msg_ids:
                    print("Unexpected msg id done while checking for

ntf", decoded)
continue

tools/net/ynl/lib/ynl.py +2 -2

@@ -980,7 +981,7 @@ class YnlFamily(SpecFamily):
                    if nl_msg.extack:
                        self._decode_extack(req_msg, op, nl_msg.extack)
                else:
-                    op = self.rsp_by_value[nl_msg.cmd()]
+                    op = None
                    req_flags = []
 
                if nl_msg.error:

@@ -1004,7 +1005,7 @@ class YnlFamily(SpecFamily):
                    done = len(reqs_by_seq) == 0
                    break
 
-                decoded = self.nlproto.decode(self, nl_msg, op)
+                decoded = self.nlproto.decode(self, nl_msg, op,
 self.rsp_by_value)
 
                # Check if this is a reply to our request

if nl_msg.nl_seq not in reqs_by_seq or decoded.cmd()
!= op.rsp_value: