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pf: Add a sysctl to limit work done for rdr source port rewriting

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It was pointed out that the current approach of exhaustively searching
for a free source port might be very time consuming.  Limit the amount
of work that we might do before giving up.

Reviewed by:	kp
Reported by:	Eirik Øverby <ltning-freebsd@anduin.net>
MFC after:	3 months
Sponsored by:	Klara, Inc.
Sponsored by:	Modirum
Differential Revision:	https://reviews.freebsd.org/D46495
This commit is contained in:
Mark Johnston 2024-09-10 14:33:47 +00:00
parent 001ca4955e
commit 339a1977c3
3 changed files with 27 additions and 4 deletions
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7
share/man/man4/pf.4
View file

@ -102,8 +102,13 @@ This tells
.Nm
to also filter on the loopback output hook.
This is typically used to allow redirect rules to adjust the source address.
.It net.pf.request_maxcount
.It Va net.pf.request_maxcount
The maximum number of items in a single ioctl call.
.It Va net.pf.rdr_srcport_rewrite_tries
The maximum number of times to try and find a free source port when handling
redirects.
Such rules are typically applied to external traffic, so an exhaustive search
may be too expensive.
.El
.Pp
Read only

6
share/man/man5/pf.conf.5
View file

@ -1407,7 +1407,11 @@ A
.Ar rdr
rule may cause the source port to be modified if doing so avoids a conflict
with an existing connection.
A random source port in the range 50001-65535 is chosen in this case.
A random source port in the range 50001-65535 is chosen in this case; to
avoid excessive CPU consumption, the number of searches for a free port is
limited by the
.Va net.pf.rdr_srcport_rewrite_tries
sysctl.
Port numbers are never translated with a
.Ar binat
rule.

18
sys/netpfil/pf/pf_lb.c
View file

@ -52,6 +52,13 @@
#include <net/pfvar.h>
#include <net/if_pflog.h>
/*
* Limit the amount of work we do to find a free source port for redirects that
* introduce a state conflict.
*/
#define V_pf_rdr_srcport_rewrite_tries VNET(pf_rdr_srcport_rewrite_tries)
VNET_DEFINE_STATIC(int, pf_rdr_srcport_rewrite_tries) = 16;
#define DPFPRINTF(n, x) if (V_pf_status.debug >= (n)) printf x
static void pf_hash(struct pf_addr *, struct pf_addr *,
@ -822,6 +829,7 @@ pf_get_translation(struct pf_pdesc *pd, struct mbuf *m, int off,
break;
case PF_RDR: {
struct pf_state_key_cmp key;
int tries;
uint16_t cut, low, high, nport;
reason = pf_map_addr(pd->af, r, saddr, naddr, NULL, NULL, sn);
@ -873,11 +881,15 @@ pf_get_translation(struct pf_pdesc *pd, struct mbuf *m, int off,
if (!pf_find_state_all_exists(&key, PF_OUT))
break;
tries = 0;
low = 50001; /* XXX-MJ PF_NAT_PROXY_PORT_LOW/HIGH */
high = 65535;
cut = arc4random() % (1 + high - low) + low;
for (uint32_t tmp = cut;
tmp <= high && tmp <= UINT16_MAX; tmp++) {
tmp <= high && tmp <= UINT16_MAX &&
tries < V_pf_rdr_srcport_rewrite_tries;
tmp++, tries++) {
key.port[0] = htons(tmp);
if (!pf_find_state_all_exists(&key, PF_OUT)) {
/* Update the source port. */
@ -885,7 +897,9 @@ pf_get_translation(struct pf_pdesc *pd, struct mbuf *m, int off,
goto out;
}
}
for (uint32_t tmp = cut - 1; tmp >= low; tmp--) {
for (uint32_t tmp = cut - 1;
tmp >= low && tries < V_pf_rdr_srcport_rewrite_tries;
tmp--, tries++) {
key.port[0] = htons(tmp);
if (!pf_find_state_all_exists(&key, PF_OUT)) {
/* Update the source port. */