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Author SHA1 Message Date
Jan Schär 7177d374a7
Merge c803c0e9e7 into a24f918d08 2025-03-13 10:25:50 +01:00
Jan Schär c803c0e9e7 Deprecate Rule.Flags field 
The functionality added in a46119e5 never worked: If you set
NFTA_RULE_POSITION to 0, the kernel will just complain that a rule with
this handle does not exist. This removes the broken functionality,
leaving the field deprecated.

https://github.com/google/nftables/issues/126 mentions that the nft
command allows referring to rules by index. But here is a quote from the
nft manpage:

> The add and insert commands support an optional location specifier,
> which is either a handle or the index (starting at zero) of an
> existing rule. Internally, rule locations are always identified by
> handle and the translation from index happens in userspace.

In other words, identifiying rules by index is a feature of nft and is
not part of the kernel interface.
 2025-03-03 13:29:31 +01:00
Jan Schär 586337f5ce Set rule handle during flush 
This change makes it possible to delete rules after inserting them,
without needing to query the rules first. Rules can be deleted both
before and after they are flushed. Additionally, this allows positioning
a new rule next to an existing rule, both before and after the existing
rule is flushed.

There are two ways to refer to a rule: Either by ID or by handle. The ID
is assigned by userspace, and is only valid within a transaction, so it
can only be used before the flush. The handle is assigned by the kernel
when the transaction is committed, and can thus only be used after the
flush. We thus need to set an ID on each newly created rule, and
retrieve the handle of the rule during the flush.

There was an existing mechanism to allocate IDs for sets, but this was
using a global counter without any synchronization to prevent data
races. I replaced this by a new mechanism which uses a connection-scoped
counter.

I implemented a new mechanism for retrieving replies in Flush, and
handling these replies by adding a callback to netlink messages. There
was some existing code to handle "overrun", which I deleted, because it
was nonsensical and just worked by accident. NLMSG_OVERRUN is in fact
not a flag, but a complete message type, so the (re&netlink.Overrun)
masking makes no sense. Even better, NLMSG_OVERRUN is never actually
used by Linux. What this code was actually doing was skipping over the
NFT_MSG_NEWRULE replies, and possibly a NFT_MSG_NEWGEN reply.

I had to update all existing tests which compared generated netlink
messages against a reference, by inserting the newly added ID attribute.
We also need to generate replies for the NFT_MSG_NEWRULE messages with a
handle added.
 2025-03-03 13:29:31 +01:00
1 changed files with 11 additions and 14 deletions
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25
rule.go
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@ -31,7 +31,6 @@ const (
)
// This constant is missing at unix.NFTA_RULE_POSITION_ID.
// TODO: Add the constant in unix and then remove it here.
const nfta_rule_position_id = 0xa
type ruleOperation uint32
@ -48,6 +47,15 @@ const (
type Rule struct {
Table *Table
Chain *Chain
// Position can be set to the Handle of another Rule to insert the new Rule
// before (InsertRule) or after (AddRule) the existing rule.
Position uint64
// Deprecated: The feature for which this field was added never worked.
// The field may be removed in a later version.
Flags uint32
// PositionID can be set to the ID of another Rule, same as Position, for when
// the existing rule is not yet committed.
PositionID uint32
// Handle identifies an existing Rule. For a new Rule, this field is set
// during the Flush() in which the rule is committed. Make sure to not access
// this field concurrently with this Flush() to avoid data races.
@ -55,18 +63,7 @@ type Rule struct {
// ID is an identifier for a new Rule, which is assigned by
// AddRule/InsertRule, and only valid before the rule is committed by Flush().
// The field is set to 0 during Flush().
ID uint32
// Position can be set to the Handle of another Rule to insert the new Rule
// before (InsertRule) or after (AddRule) the existing rule.
Position uint64
// PositionID can be set to the ID of another Rule, same as Position, for when
// the existing rule is not yet committed.
PositionID uint32
// The list of possible flags are specified by nftnl_rule_attr, see
// https://git.netfilter.org/libnftnl/tree/include/libnftnl/rule.h#n21
// Current nftables go implementation supports only
// NFTNL_RULE_POSITION flag for setting rule at position 0
Flags uint32
ID uint32
Exprs []expr.Any
UserData []byte
}
@ -186,7 +183,7 @@ func (cc *Conn) newRule(r *Rule, op ruleOperation) *Rule {
flags = netlink.Request | netlink.Acknowledge | netlink.Replace
}
if r.Position != 0 || (r.Flags&(1<<unix.NFTA_RULE_POSITION)) != 0 {
if r.Position != 0 {
msgData = append(msgData, cc.marshalAttr([]netlink.Attribute{
{Type: unix.NFTA_RULE_POSITION, Data: binaryutil.BigEndian.PutUint64(r.Position)},
})...)