From 1fa3314c14c6a20d098991a0a6980f9b18b2f930 Mon Sep 17 00:00:00 2001 From: Ido Schimmel Date: Wed, 14 Aug 2024 15:52:24 +0300 Subject: [PATCH] ipv4: Centralize TOS matching The TOS field in the IPv4 flow information structure ('flowi4_tos') is matched by the kernel against the TOS selector in IPv4 rules and routes. The field is initialized differently by different call sites. Some treat it as DSCP (RFC 2474) and initialize all six DSCP bits, some treat it as RFC 1349 TOS and initialize it using RT_TOS() and some treat it as RFC 791 TOS and initialize it using IPTOS_RT_MASK. What is common to all these call sites is that they all initialize the lower three DSCP bits, which fits the TOS definition in the initial IPv4 specification (RFC 791). Therefore, the kernel only allows configuring IPv4 FIB rules that match on the lower three DSCP bits which are always guaranteed to be initialized by all call sites: # ip -4 rule add tos 0x1c table 100 # ip -4 rule add tos 0x3c table 100 Error: Invalid tos. While this works, it is unlikely to be very useful. RFC 791 that initially defined the TOS and IP precedence fields was updated by RFC 2474 over twenty five years ago where these fields were replaced by a single six bits DSCP field. Extending FIB rules to match on DSCP can be done by adding a new DSCP selector while maintaining the existing semantics of the TOS selector for applications that rely on that. A prerequisite for allowing FIB rules to match on DSCP is to adjust all the call sites to initialize the high order DSCP bits and remove their masking along the path to the core where the field is matched on. However, making this change alone will result in a behavior change. For example, a forwarded IPv4 packet with a DS field of 0xfc will no longer match a FIB rule that was configured with 'tos 0x1c'. This behavior change can be avoided by masking the upper three DSCP bits in 'flowi4_tos' before comparing it against the TOS selectors in FIB rules and routes. Implement the above by adding a new function that checks whether a given DSCP value matches the one specified in the IPv4 flow information structure and invoke it from the three places that currently match on 'flowi4_tos'. Use RT_TOS() for the masking of 'flowi4_tos' instead of IPTOS_RT_MASK since the latter is not uAPI and we should be able to remove it at some point. Include in since the former defines IPTOS_TOS_MASK which is used in the definition of RT_TOS() in . No regressions in FIB tests: # ./fib_tests.sh [...] Tests passed: 218 Tests failed: 0 And FIB rule tests: # ./fib_rule_tests.sh [...] Tests passed: 116 Tests failed: 0 Signed-off-by: Ido Schimmel Signed-off-by: Paolo Abeni --- include/net/ip_fib.h | 6 ++++++ include/uapi/linux/in_route.h | 2 ++ net/ipv4/fib_rules.c | 2 +- net/ipv4/fib_semantics.c | 3 +-- net/ipv4/fib_trie.c | 3 +-- 5 files changed, 11 insertions(+), 5 deletions(-) diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h index 72af2f223e591..269ec10f63e45 100644 --- a/include/net/ip_fib.h +++ b/include/net/ip_fib.h @@ -22,6 +22,7 @@ #include #include #include +#include struct fib_config { u8 fc_dst_len; @@ -434,6 +435,11 @@ static inline bool fib4_rules_early_flow_dissect(struct net *net, #endif /* CONFIG_IP_MULTIPLE_TABLES */ +static inline bool fib_dscp_masked_match(dscp_t dscp, const struct flowi4 *fl4) +{ + return dscp == inet_dsfield_to_dscp(RT_TOS(fl4->flowi4_tos)); +} + /* Exported by fib_frontend.c */ extern const struct nla_policy rtm_ipv4_policy[]; void ip_fib_init(void); diff --git a/include/uapi/linux/in_route.h b/include/uapi/linux/in_route.h index 0cc2c23b47f84..10bdd7e7107fa 100644 --- a/include/uapi/linux/in_route.h +++ b/include/uapi/linux/in_route.h @@ -2,6 +2,8 @@ #ifndef _LINUX_IN_ROUTE_H #define _LINUX_IN_ROUTE_H +#include + /* IPv4 routing cache flags */ #define RTCF_DEAD RTNH_F_DEAD diff --git a/net/ipv4/fib_rules.c b/net/ipv4/fib_rules.c index 5bdd1c0160094..c26776b71e97f 100644 --- a/net/ipv4/fib_rules.c +++ b/net/ipv4/fib_rules.c @@ -186,7 +186,7 @@ INDIRECT_CALLABLE_SCOPE int fib4_rule_match(struct fib_rule *rule, ((daddr ^ r->dst) & r->dstmask)) return 0; - if (r->dscp && r->dscp != inet_dsfield_to_dscp(fl4->flowi4_tos)) + if (r->dscp && !fib_dscp_masked_match(r->dscp, fl4)) return 0; if (rule->ip_proto && (rule->ip_proto != fl4->flowi4_proto)) diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c index 2b57cd2b96e2a..0f70341cb8b5e 100644 --- a/net/ipv4/fib_semantics.c +++ b/net/ipv4/fib_semantics.c @@ -2066,8 +2066,7 @@ static void fib_select_default(const struct flowi4 *flp, struct fib_result *res) if (fa->fa_slen != slen) continue; - if (fa->fa_dscp && - fa->fa_dscp != inet_dsfield_to_dscp(flp->flowi4_tos)) + if (fa->fa_dscp && !fib_dscp_masked_match(fa->fa_dscp, flp)) continue; if (fa->tb_id != tb->tb_id) continue; diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c index 8f30e3f00b7f2..09e31757e96c7 100644 --- a/net/ipv4/fib_trie.c +++ b/net/ipv4/fib_trie.c @@ -1580,8 +1580,7 @@ int fib_table_lookup(struct fib_table *tb, const struct flowi4 *flp, if (index >= (1ul << fa->fa_slen)) continue; } - if (fa->fa_dscp && - inet_dscp_to_dsfield(fa->fa_dscp) != flp->flowi4_tos) + if (fa->fa_dscp && !fib_dscp_masked_match(fa->fa_dscp, flp)) continue; /* Paired with WRITE_ONCE() in fib_release_info() */ if (READ_ONCE(fi->fib_dead))