Fix AclSize computation: issue #4831 (#4832)

Co-authored-by: Ebrix <[email protected]>

Author: Ebrix

scapy/layers/smb2.py

@@ -1505,8 +1505,14 @@ class WINNT_ACL(Packet):
     fields_desc = [
         ByteField("AclRevision", 2),
         ByteField("Sbz1", 0x00),
+        # Total size including header:
+        # AclRevision(1) + Sbz1(1) + AclSize(2) + AceCount(2) + Sbz2(2)
         FieldLenField(
-            "AclSize", None, length_of="Aces", adjust=lambda _, x: x + 14, fmt="<H"
+            "AclSize",
+            None,
+            length_of="Aces",
+            adjust=lambda _, x: x + 8,
+            fmt="<H",
         ),
         FieldLenField("AceCount", None, count_of="Aces", fmt="<H"),
         ShortField("Sbz2", 0),

test/scapy/layers/smb2.uts

@@ -575,3 +575,5 @@ assert sd.DACLOffset == 44
 assert sd.OwnerSid.summary() == "S-1-1-0"
 assert sd.GroupSid.summary() == "S-1-1-0"
 assert sd.DACL.toSDDL() == ['(A;;;;;S-1-1-0)']
+
+assert sd.DACL.AclSize == len(sd.DACL)