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BGP: Setting and unsetting unknown attributes

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All these must be declared as bytestring. Allows operators to delete
unwanted attributes breaking the Internet:

    https://blog.benjojo.co.uk/post/bgp-path-attributes-grave-error-handling
This commit is contained in:
katerina.kubecova 2023-09-19 11:11:24 +02:00 committed by Maria Matejka
parent cc122bf0c2
commit a0fb0eaa67
5 changed files with 34 additions and 2 deletions
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7
doc/bird.sgml
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@ -3287,6 +3287,13 @@ some of them (marked with `<tt/O/') are optional.
name="local Role"> is configured it set automatically.
</descrip>
<p>For attributes unknown by BIRD, the user can assign a name (on top level)
to an attribute by its number. This defined name can be used then to both set
(by a bytestring literal, transitive) or unset the given attribute even though
BIRD knows nothing about it:
<tt><label id="bgp-attribute-custom">attribute bgp <m/number/ bytestring <m/name/;</tt>
<sect1>Example
<label id="bgp-exam">

1
filter/data.h
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@ -99,6 +99,7 @@ struct f_dynamic_attr {
u8 bit; /* For bitfield accessors */
enum f_type f_type; /* Filter type */
uint ea_code; /* EA code */
uint flags;
};
enum f_sa_code {

2
filter/f-inst.c
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@ -857,7 +857,7 @@
l->flags = EALF_SORTED;
l->count = 1;
l->attrs[0].id = da.ea_code;
l->attrs[0].flags = 0;
l->attrs[0].flags = da.flags;
l->attrs[0].type = da.type;
l->attrs[0].originated = 1;
l->attrs[0].fresh = 1;

15
filter/f-inst.h
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@ -118,6 +118,21 @@ static inline struct f_dynamic_attr f_new_dynamic_attr_bit(u8 bit, enum f_type f
static inline struct f_static_attr f_new_static_attr(int f_type, int code, int readonly)
{ return (struct f_static_attr) { .f_type = f_type, .sa_code = code, .readonly = readonly }; }
static inline int f_type_attr(int f_type) {
switch (f_type) {
case T_INT: return EAF_TYPE_INT;
case T_IP: return EAF_TYPE_IP_ADDRESS;
case T_QUAD: return EAF_TYPE_ROUTER_ID;
case T_PATH: return EAF_TYPE_AS_PATH;
case T_CLIST: return EAF_TYPE_INT_SET;
case T_ECLIST: return EAF_TYPE_EC_SET;
case T_LCLIST: return EAF_TYPE_LC_SET;
case T_BYTESTRING: return EAF_TYPE_OPAQUE;
default:
cf_error("Custom route attribute of unsupported type");
}
}
/* Hook for call bt_assert() function in configuration */
extern void (*bt_assert_hook)(int result, const struct f_line_item *assert);

11
proto/bgp/config.Y
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@ -362,7 +362,16 @@ dynamic_attr: BGP_LARGE_COMMUNITY
dynamic_attr: BGP_OTC
{ $$ = f_new_dynamic_attr(EAF_TYPE_INT, T_INT, EA_CODE(PROTOCOL_BGP, BA_ONLY_TO_CUSTOMER)); } ;
custom_attr: ATTRIBUTE BGP NUM type symbol ';' {
if($3 > 255 || $3 < 1)
cf_error("Invalid attribute number. (Given %i, must be 1-255.)", $3);
if($4 != T_BYTESTRING)
cf_error("Attribute type must be bytestring, not %s.", f_type_name($4));
struct f_dynamic_attr* a = (struct f_dynamic_attr*) malloc(sizeof(struct f_dynamic_attr));
*a = f_new_dynamic_attr(f_type_attr($4), T_BYTESTRING, EA_CODE(PROTOCOL_BGP, $3));
a->flags = BAF_TRANSITIVE | BAF_OPTIONAL;
cf_define_symbol(new_config, $5, SYM_ATTRIBUTE, attribute, a);
};
CF_ENUM(T_ENUM_BGP_ORIGIN, ORIGIN_, IGP, EGP, INCOMPLETE)