[PATCH net v2 1/4] ipv4: add FIB_LOOKUP_REPORT_MISS

[liamsmith827 <liamsmith827@grapheneos.org>]

From: liamsmith827 <liamsmith827@proton.me>

IPv4 FIB lookup maps a routing miss to -ENETUNREACH, which is also
returned when an unreachable rule is encountered. This flag prevents the
mapping, returning -ESRCH instead.

Cc: stable@vger.kernel.org
Signed-off-by: liamsmith827 <liamsmith827@proton.me>
---
 include/net/fib_rules.h | 5 +++++
 include/net/ip_fib.h    | 6 +++---
 net/ipv4/fib_rules.c    | 2 +-
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/include/net/fib_rules.h b/include/net/fib_rules.h
index c6b94790fa81..bcb6809dbd10 100644
--- a/include/net/fib_rules.h
+++ b/include/net/fib_rules.h
@@ -59,6 +59,11 @@ struct fib_lookup_arg {
 	int			flags;
 #define FIB_LOOKUP_NOREF		1
 #define FIB_LOOKUP_IGNORE_LINKSTATE	2
+/* Return -ESRCH instead of mapping it to -ENETUNREACH. Only applies to IPv4
+ * lookups. When used with FIB_LOOKUP_NOREF, -ESRCH indicates the lookup
+ * exhausted all rules and tables without finding a usable route.
+ */
+#define FIB_LOOKUP_REPORT_MISS		4
 };
 
 struct fib_rules_ops {
diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 92f4eb8b86d7..d0b4f261585a 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -318,7 +318,7 @@ static inline int fib_lookup(struct net *net, const struct flowi4 *flp,
 			     struct fib_result *res, unsigned int flags)
 {
 	struct fib_table *tb;
-	int err = -ENETUNREACH;
+	int err = -EAGAIN;
 
 	rcu_read_lock();
 
@@ -327,7 +327,7 @@ static inline int fib_lookup(struct net *net, const struct flowi4 *flp,
 		err = fib_table_lookup(tb, flp, res, flags | FIB_LOOKUP_NOREF);
 
 	if (err == -EAGAIN)
-		err = -ENETUNREACH;
+		err = (flags & FIB_LOOKUP_REPORT_MISS) ? -ESRCH : -ENETUNREACH;
 
 	rcu_read_unlock();
 
@@ -398,7 +398,7 @@ static inline int fib_lookup(struct net *net, struct flowi4 *flp,
 		err = fib_table_lookup(tb, flp, res, flags);
 
 	if (err == -EAGAIN)
-		err = -ENETUNREACH;
+		err = (flags & FIB_LOOKUP_REPORT_MISS) ? -ESRCH : -ENETUNREACH;
 out:
 	rcu_read_unlock();
 
diff --git a/net/ipv4/fib_rules.c b/net/ipv4/fib_rules.c
index 060501b376a8..3d7dcb8d0865 100644
--- a/net/ipv4/fib_rules.c
+++ b/net/ipv4/fib_rules.c
@@ -101,7 +101,7 @@ int __fib_lookup(struct net *net, struct flowi4 *flp,
 		res->tclassid = 0;
 #endif
 
-	if (err == -ESRCH)
+	if (err == -ESRCH && !(flags & FIB_LOOKUP_REPORT_MISS))
 		err = -ENETUNREACH;
 
 	return err;
-- 
2.47.3