mergesort: Avoid accidental set element reordering

In corner cases, expr_msort_cmp() may return 0 for two non-identical
elements. An example are ORed tcp flags: 'syn' and 'syn | ack' are
considered the same value since expr_msort_value() reduces the latter to
its LHS.

Keeping the above in mind and looking at how list_expr_sort() works: The
list in 'head' is cut in half, the first half put into the temporary
list 'list' and finally 'list' is merged back into 'head' considering
each element's position. Shall expr_msort_cmp() return 0 for two
elements, the one from 'list' ends up after the one in 'head', thus
reverting their previous ordering.

The practical implication is that output never matches input for the
sample set '{ syn, syn | ack }' as the sorting after delinearization in
netlink_list_setelems() keeps swapping the elements. Out of coincidence,
the commit this fixes itself illustrates the use-case this breaks,
namely tracking a ruleset in git: Each ruleset reload will trigger an
update to the stored dump.

This change breaks interval set element deletion because __set_delete()
implicitly relies upon this reordering of duplicate entries by inserting
a clone of the one to delete into the start (via list_move()) and after
sorting assumes the clone will end up right behind the original. Fix
this by calling list_move_tail() instead.

Fixes: 14ee0a979b622 ("src: sort set elements in netlink_get_setelems()")
Signed-off-by: Phil Sutter <phil@nwl.cc>

diff --git a/src/intervals.c b/src/intervals.c
index 68728349e999c6875caa3213c7126410e415e0c2..6c3f36fec02aae3c412f8cb5924f687fc05c8893 100644 (file)
--- a/src/intervals.c
+++ b/src/intervals.c
@@ -466,7 +466,7 @@ static int __set_delete(struct list_head *msgs, struct expr *i,     struct set *set,
                        unsigned int debug_mask)
 {
        i->flags |= EXPR_F_REMOVE;
-       list_move(&i->list, &existing_set->init->expressions);
+       list_move_tail(&i->list, &existing_set->init->expressions);
        list_expr_sort(&existing_set->init->expressions);
 
        return setelem_delete(msgs, set, init, existing_set->init, debug_mask);

diff --git a/src/mergesort.c b/src/mergesort.c
index 4d0e280fdc5e22cf07021388a48a239c9a4ef982..5e676be16369b59f51002e78ab4a7ec290192fb7 100644 (file)
--- a/src/mergesort.c
+++ b/src/mergesort.c
@@ -78,7 +78,7 @@ void list_splice_sorted(struct list_head *list, struct list_head *head)
        while (l != list) {
                if (h == head ||
                    expr_msort_cmp(list_entry(l, typeof(struct expr), list),
-                                  list_entry(h, typeof(struct expr), list)) < 0) {
+                                  list_entry(h, typeof(struct expr), list)) <= 0) {
                        l = l->next;
                        list_add_tail(l->prev, h);
                        continue;

diff --git a/tests/shell/testcases/sets/dumps/0055tcpflags_0.json-nft b/tests/shell/testcases/sets/dumps/0055tcpflags_0.json-nft
index 6a3511515f78513cc87799ba73782bb0020a4489..e37139f334466102cc2016e8c576131a6e3066c4 100644 (file)
--- a/tests/shell/testcases/sets/dumps/0055tcpflags_0.json-nft
+++ b/tests/shell/testcases/sets/dumps/0055tcpflags_0.json-nft
@@ -28,15 +28,6 @@
           {
             "|": [
               "fin",
-              "psh",
-              "ack",
-              "urg"
-            ]
-          },
-          {
-            "|": [
-              "fin",
-              "psh",
               "ack"
             ]
           },
@@ -50,21 +41,22 @@
           {
             "|": [
               "fin",
+              "psh",
               "ack"
             ]
           },
           {
             "|": [
-              "syn",
+              "fin",
               "psh",
               "ack",
               "urg"
             ]
           },
+          "syn",
           {
             "|": [
               "syn",
-              "psh",
               "ack"
             ]
           },
@@ -78,22 +70,22 @@
           {
             "|": [
               "syn",
+              "psh",
               "ack"
             ]
           },
-          "syn",
           {
             "|": [
-              "rst",
+              "syn",
               "psh",
               "ack",
               "urg"
             ]
           },
+          "rst",
           {
             "|": [
               "rst",
-              "psh",
               "ack"
             ]
           },
@@ -107,12 +99,13 @@
           {
             "|": [
               "rst",
+              "psh",
               "ack"
             ]
           },
-          "rst",
           {
             "|": [
+              "rst",
               "psh",
               "ack",
               "urg"
@@ -126,11 +119,18 @@
           },
           {
             "|": [
+              "psh",
               "ack",
               "urg"
             ]
           },
-          "ack"
+          "ack",
+          {
+            "|": [
+              "ack",
+              "urg"
+            ]
+          }
         ]
       }
     }

diff --git a/tests/shell/testcases/sets/dumps/0055tcpflags_0.nft b/tests/shell/testcases/sets/dumps/0055tcpflags_0.nft
index ffed5426577e4190206cb22dfe9918075da651fe..22bf5c461b8779d1e3370e4571137c5b53a8bdc1 100644 (file)
--- a/tests/shell/testcases/sets/dumps/0055tcpflags_0.nft
+++ b/tests/shell/testcases/sets/dumps/0055tcpflags_0.nft
@@ -2,9 +2,9 @@ table ip test {
        set tcp_good_flags {
                type tcp_flag
                flags constant
-               elements = { fin | psh | ack | urg, fin | psh | ack, fin | ack | urg, fin | ack, syn | psh | ack | urg,
-                            syn | psh | ack, syn | ack | urg, syn | ack, syn, rst | psh | ack | urg,
-                            rst | psh | ack, rst | ack | urg, rst | ack, rst, psh | ack | urg,
-                            psh | ack, ack | urg, ack }
+               elements = { fin | ack, fin | ack | urg, fin | psh | ack, fin | psh | ack | urg, syn,
+                            syn | ack, syn | ack | urg, syn | psh | ack, syn | psh | ack | urg, rst,
+                            rst | ack, rst | ack | urg, rst | psh | ack, rst | psh | ack | urg, psh | ack,
+                            psh | ack | urg, ack, ack | urg }
        }
 }