git: 25392fac9488 - main - libalias: Fix splay comparsion bug

[Lutz Donnerhacke]

The branch main has been updated by donner:

URL: https://cgit.FreeBSD.org/src/commit/?id=25392fac9488bcae5c451500df2e2945430484a6

commit 25392fac9488bcae5c451500df2e2945430484a6
Author:     Lutz Donnerhacke <donner at FreeBSD.org>
AuthorDate: 2021-07-02 21:41:25 +0000
Commit:     Lutz Donnerhacke <donner at FreeBSD.org>
CommitDate: 2021-07-02 22:31:53 +0000

    libalias: Fix splay comparsion bug
    
    Comparing elements in a tree requires transitiviy.  If a < b and b < c
    then a must be smaller than c.  This way the tree elements are always
    pairwise comparable.
    
    Tristate comparsion functions returning values lower, equal, or
    greater than zero, are usually implemented by a simple subtraction of
    the operands.  If the size of the operands are equal to the size of
    the result, integer modular arithmetics kick in and violates the
    transitivity.
    
    Example:
    Working on byte with 0, 120, and 240. Now computing the differences:
      120 -   0 = 120
      240 - 120 = 120
      240 -   0 = -16
    
    MFC after:      3 days
---
 sys/netinet/libalias/alias_db.h | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/sys/netinet/libalias/alias_db.h b/sys/netinet/libalias/alias_db.h
index ec0b69c01f82..971ca305c1a6 100644
--- a/sys/netinet/libalias/alias_db.h
+++ b/sys/netinet/libalias/alias_db.h
@@ -351,10 +351,10 @@ static inline int
 cmp_out(struct alias_link *a, struct alias_link *b) {
 	int i = a->src_port - b->src_port;
 	if (i != 0) return (i);
-	i = a->src_addr.s_addr - b->src_addr.s_addr;
-	if (i != 0) return (i);
-	i = a->dst_addr.s_addr - b->dst_addr.s_addr;
-	if (i != 0) return (i);
+	if (a->src_addr.s_addr > b->src_addr.s_addr) return (1);
+	if (a->src_addr.s_addr < b->src_addr.s_addr) return (-1);
+	if (a->dst_addr.s_addr > b->dst_addr.s_addr) return (1);
+	if (a->dst_addr.s_addr < b->dst_addr.s_addr) return (-1);
 	i = a->dst_port - b->dst_port;
 	if (i != 0) return (i);
 	i = a->link_type - b->link_type;
@@ -368,8 +368,9 @@ cmp_in(struct group_in *a, struct group_in *b) {
 	if (i != 0) return (i);
 	i = a->link_type - b->link_type;
 	if (i != 0) return (i);
-	i = a->alias_addr.s_addr - b->alias_addr.s_addr;
-	return (i);
+	if (a->alias_addr.s_addr > b->alias_addr.s_addr) return (1);
+	if (a->alias_addr.s_addr < b->alias_addr.s_addr) return (-1);
+	return (0);
 }
 SPLAY_PROTOTYPE(splay_in, group_in, in, cmp_in);