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netfilter: nf_tables: zero timeout means element never times out

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This patch uses zero as timeout marker for those elements that never expire
when the element is created.

If userspace provides no timeout for an element, then the default set
timeout applies. However, if no default set timeout is specified and
timeout flag is set on, then timeout extension is allocated and timeout
is set to zero to allow for future updates.

Use of zero a never timeout marker has been suggested by Phil Sutter.

Note that, in older kernels, it is already possible to define elements
that never expire by declaring a set with the set timeout flag set on
and no global set timeout, in this case, new element with no explicit
timeout never expire do not allocate the timeout extension, hence, they
never expire. This approach makes it complicated to accomodate element
timeout update, because element extensions do not support reallocations.
Therefore, allocate the timeout extension and use the new marker for
this case, but do not expose it to userspace to retain backward
compatibility in the set listing.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Pablo Neira Ayuso
2024-09-03 01:09:27 +02:00
parent 4c5daea9af
commit 8bfb74ae12
4 changed files with 31 additions and 20 deletions
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include/uapi/linux/netfilter/nf_tables.h
+1 -1
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@@ -436,7 +436,7 @@ enum nft_set_elem_flags {
* @NFTA_SET_ELEM_KEY: key value (NLA_NESTED: nft_data)
* @NFTA_SET_ELEM_DATA: data value of mapping (NLA_NESTED: nft_data_attributes)
* @NFTA_SET_ELEM_FLAGS: bitmask of nft_set_elem_flags (NLA_U32)
* @NFTA_SET_ELEM_TIMEOUT: timeout value (NLA_U64)
* @NFTA_SET_ELEM_TIMEOUT: timeout value, zero means never times out (NLA_U64)
* @NFTA_SET_ELEM_EXPIRATION: expiration time (NLA_U64)
* @NFTA_SET_ELEM_USERDATA: user data (NLA_BINARY)
* @NFTA_SET_ELEM_EXPR: expression (NLA_NESTED: nft_expr_attributes)