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netfilter: x_tables: make xt_replace_table wait until old rules are not used anymore

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xt_replace_table relies on table replacement counter retrieval (which
uses xt_recseq to synchronize pcpu counters).

This is fine, however with large rule set get_counters() can take
a very long time -- it needs to synchronize all counters because
it has to assume concurrent modifications can occur.

Make xt_replace_table synchronize by itself by waiting until all cpus
had an even seqcount.

This allows a followup patch to copy the counters of the old ruleset
without any synchonization after xt_replace_table has completed.

Cc: Dan Williams <dcbw@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2017-10-12 01:13:50 +02:00 committed by Pablo Neira Ayuso
parent eb6fad5a4a
commit 80055dab5d
1 changed files with 18 additions and 3 deletions
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21
net/netfilter/x_tables.c
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@ -1153,6 +1153,7 @@ xt_replace_table(struct xt_table *table,
int *error)
{
struct xt_table_info *private;
unsigned int cpu;
int ret;
ret = xt_jumpstack_alloc(newinfo);
@ -1182,14 +1183,28 @@ xt_replace_table(struct xt_table *table,
smp_wmb();
table->private = newinfo;
/* make sure all cpus see new ->private value */
smp_wmb();
/*
* Even though table entries have now been swapped, other CPU's
* may still be using the old entries. This is okay, because
* resynchronization happens because of the locking done
* during the get_counters() routine.
* may still be using the old entries...
*/
local_bh_enable();
/* ... so wait for even xt_recseq on all cpus */
for_each_possible_cpu(cpu) {
seqcount_t *s = &per_cpu(xt_recseq, cpu);
u32 seq = raw_read_seqcount(s);
if (seq & 1) {
do {
cond_resched();
cpu_relax();
} while (seq == raw_read_seqcount(s));
}
}
#ifdef CONFIG_AUDIT
if (audit_enabled) {
audit_log(current->audit_context, GFP_KERNEL,