ipv4: Convert ->flowi4_tos to dscp_t.

Convert the ->flowic_tos field of struct flowi_common from __u8 to
dscp_t, rename it ->flowic_dscp and propagate these changes to struct
flowi and struct flowi4.

We've had several bugs in the past where ECN bits could interfere with
IPv4 routing, because these bits were not properly cleared when setting
->flowi4_tos. These bugs should be fixed now and the dscp_t type has
been introduced to ensure that variables carrying DSCP values don't
accidentally have any ECN bits set. Several variables and structure
fields have been converted to dscp_t already, but the main IPv4 routing
structure, struct flowi4, is still using a __u8. To avoid any future
regression, this patch converts it to dscp_t.

There are many users to convert at once. Fortunately, around half of
->flowi4_tos users already have a dscp_t value at hand, which they
currently convert to __u8 using inet_dscp_to_dsfield(). For all of
these users, we just need to drop that conversion.

But, although we try to do the __u8 <-> dscp_t conversions at the
boundaries of the network or of user space, some places still store
TOS/DSCP variables as __u8 in core networking code. Those can hardly be
converted either because the data structure is part of UAPI or because
the same variable or field is also used for handling ECN in other parts
of the code. In all of these cases where we don't have a dscp_t
variable at hand, we need to use inet_dsfield_to_dscp() when
interacting with ->flowi4_dscp.

Changes since v1:
  * Fix space alignment in __bpf_redirect_neigh_v4() (Ido).

Signed-off-by: Guillaume Nault <gnault@redhat.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/29acecb45e911d17446b9a3dbdb1ab7b821ea371.1756128932.git.gnault@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/include/net/flow.h b/include/net/flow.h
index a1839c278d87..ae9481c40063 100644
--- a/include/net/flow.h
+++ b/include/net/flow.h
@@ -12,6 +12,7 @@
 #include <linux/atomic.h>
 #include <linux/container_of.h>
 #include <linux/uidgid.h>
+#include <net/inet_dscp.h>
 
 struct flow_keys;
 
@@ -32,7 +33,7 @@ struct flowi_common {
 	int	flowic_iif;
 	int     flowic_l3mdev;
 	__u32	flowic_mark;
-	__u8	flowic_tos;
+	dscp_t	flowic_dscp;
 	__u8	flowic_scope;
 	__u8	flowic_proto;
 	__u8	flowic_flags;
@@ -70,7 +71,7 @@ struct flowi4 {
 #define flowi4_iif		__fl_common.flowic_iif
 #define flowi4_l3mdev		__fl_common.flowic_l3mdev
 #define flowi4_mark		__fl_common.flowic_mark
-#define flowi4_tos		__fl_common.flowic_tos
+#define flowi4_dscp		__fl_common.flowic_dscp
 #define flowi4_scope		__fl_common.flowic_scope
 #define flowi4_proto		__fl_common.flowic_proto
 #define flowi4_flags		__fl_common.flowic_flags
@@ -103,7 +104,7 @@ static inline void flowi4_init_output(struct flowi4 *fl4, int oif,
 	fl4->flowi4_iif = LOOPBACK_IFINDEX;
 	fl4->flowi4_l3mdev = 0;
 	fl4->flowi4_mark = mark;
-	fl4->flowi4_tos = tos;
+	fl4->flowi4_dscp = inet_dsfield_to_dscp(tos);
 	fl4->flowi4_scope = scope;
 	fl4->flowi4_proto = proto;
 	fl4->flowi4_flags = flags;
@@ -141,7 +142,7 @@ struct flowi6 {
 #define flowi6_uid		__fl_common.flowic_uid
 	struct in6_addr		daddr;
 	struct in6_addr		saddr;
-	/* Note: flowi6_tos is encoded in flowlabel, too. */
+	/* Note: flowi6_dscp is encoded in flowlabel, too. */
 	__be32			flowlabel;
 	union flowi_uli		uli;
 #define fl6_sport		uli.ports.sport
@@ -163,7 +164,7 @@ struct flowi {
 #define flowi_iif	u.__fl_common.flowic_iif
 #define flowi_l3mdev	u.__fl_common.flowic_l3mdev
 #define flowi_mark	u.__fl_common.flowic_mark
-#define flowi_tos	u.__fl_common.flowic_tos
+#define flowi_dscp	u.__fl_common.flowic_dscp
 #define flowi_scope	u.__fl_common.flowic_scope
 #define flowi_proto	u.__fl_common.flowic_proto
 #define flowi_flags	u.__fl_common.flowic_flags