dfilter: Handle null arguments to min, max

min and max need to handle null arguments where the GPtrArray
is null, generated when there have been other opcodes between
the field loading and the function. (They are ignored, not
treated as zero, so they don't change the minimum.)

Prevents crashes with filters where a field does not exist in the tree:

min(tcp.srcport * 10, tcp.dstport * 10) == 800
min(len(tcp.payload), len(udp.payload)) == 153
min(len(tcp.payload[2:]) + 2, len(udp.payload[2:]) + 2) == 153

where a register is loaded where it has not had its GPtrArray created:

./run/dftest 'min(len(tcp.payload), len(udp.payload))'
Filter:
 min(len(tcp.payload), len(udp.payload))

Instructions:
 0000 READ_TREE        tcp.payload      -> R1
 0001 IF_FALSE_GOTO    3
 0002 LENGTH           R1               -> R2
 0003 STACK_PUSH       R2
 0004 READ_TREE        udp.payload      -> R3
 0005 IF_FALSE_GOTO    7
 0006 LENGTH           R3               -> R4
 0007 STACK_PUSH       R4
 0008 CALL_FUNCTION    min(R2, R4)      -> R0
 0009 STACK_POP        [2]
 0010 IF_FALSE_GOTO    12
 0011 NOT_ALL_ZERO     R0
 0012 RETURN

Related to fcb6bb576388e8a8ef4b657d794a80f008a99ff7
(Prior to that commit, this worked because a NULL pointer is a
valid, empty GSList.)

1 files changed, 14 insertions, 0 deletions

diff --git a/test/suite_dfilter/group_function.py b/test/suite_dfilter/group_function.py
index aad95e604d..9eda540194 100644
--- a/test/suite_dfilter/group_function.py
+++ b/test/suite_dfilter/group_function.py
@@ -107,3 +107,17 @@ class TestFunctionNested:
     def test_function_nested_1(self, checkDFilterCount):
         dfilter = 'abs(min(tcp.srcport, tcp.dstport)) == 80'
         checkDFilterCount(dfilter, 1)
+
+    def test_function_nested_2(self, checkDFilterCount):
+        dfilter = 'min(tcp.srcport * 10, tcp.dstport * 10, udp.srcport * 10, udp.dstport * 10) == 800'
+        checkDFilterCount(dfilter, 1)
+
+    def test_function_nested_3(self, checkDFilterCount):
+        dfilter = 'min(len(tcp.payload), len(udp.payload)) == 153'
+        checkDFilterCount(dfilter, 1)
+
+    def test_function_nested_4(self, checkDFilterCount):
+        # udp.payload does not exist. Check that len(udp.payload) + 2
+        # resolves to NULL, not to 2.
+        dfilter = 'min(len(tcp.payload[2:]) + 2, len(udp.payload[2:]) + 2) == 153'
+        checkDFilterCount(dfilter, 1)