From 6c84ccad25890ac507320728ec42c786abc40ace Mon Sep 17 00:00:00 2001
From: Abtin Keshavarzian <abtink@google.com>
Date: Fri, 24 Nov 2023 09:11:19 -0800
Subject: [PATCH] [ip6] update Ip6::SelectSourceAddress() to prefer
 non-deprecated addresses (#9634)

This commit updates `SelectSourceAddress()` to ensure that
non-deprecated addresses are always preferred over deprecated ones.
When iterating over addresses, the best option is tracked in
`bestAddr`. If the new address is not preferred and the currently
selected `bestAddr` is, the new address is skipped to ensure that it
is not picked.
---
 src/core/net/ip6.cpp | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/core/net/ip6.cpp b/src/core/net/ip6.cpp
index b7759ef65..d5ddeecad 100644
--- a/src/core/net/ip6.cpp
+++ b/src/core/net/ip6.cpp
@@ -1366,11 +1366,19 @@ const Address *Ip6::SelectSourceAddress(const Address &aDestination) const
                 continue;
             }
         }
-        else if (addr.mPreferred && !bestAddr->mPreferred)
+        else if (addr.mPreferred != bestAddr->mPreferred)
         {
             // Rule 3: Avoid deprecated addresses
-            bestAddr     = &addr;
-            bestMatchLen = matchLen;
+
+            if (addr.mPreferred)
+            {
+                bestAddr     = &addr;
+                bestMatchLen = matchLen;
+            }
+            else
+            {
+                continue;
+            }
         }
         else if (matchLen > bestMatchLen)
         {