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tcp_input/syncache: acquire only read lock on PCB for SYN,!ACK packets

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When packet is a SYN packet, we don't need to modify any existing PCB.
Normally SYN arrives on a listening socket, we either create a syncache
entry or generate syncookie, but we don't modify anything with the
listening socket or associated PCB. Thus create a new PCB lookup
mode - rlock if listening. This removes the primary contention point
under SYN flood - the listening socket PCB.

Sidenote: when SYN arrives on a synchronized connection, we still
don't need write access to PCB to send a challenge ACK or just to
drop. There is only one exclusion - tcptw recycling. However,
existing entanglement of tcp_input + stacks doesn't allow to make
this change small. Consider this patch as first approach to the problem.

Reviewed by:	rrs
Differential revision:	https://reviews.freebsd.org/D29576
This commit is contained in:
Gleb Smirnoff 2021-03-18 19:06:13 -07:00
parent 0c6282e842
commit 08d9c92027
7 changed files with 61 additions and 67 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
sys/netinet/in_pcb.c
View File

@ -2518,31 +2518,24 @@ in_pcblookup_hash(struct inpcbinfo *pcbinfo, struct in_addr faddr,
struct inpcb *inp;
inp = in_pcblookup_hash_locked(pcbinfo, faddr, fport, laddr, lport,
(lookupflags & ~(INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB)), ifp,
numa_domain);
lookupflags & INPLOOKUP_WILDCARD, ifp, numa_domain);
if (inp != NULL) {
if (lookupflags & INPLOOKUP_WLOCKPCB) {
INP_WLOCK(inp);
if (__predict_false(inp->inp_flags2 & INP_FREED)) {
INP_WUNLOCK(inp);
inp = NULL;
}
} else if (lookupflags & INPLOOKUP_RLOCKPCB) {
INP_RLOCK(inp);
if (__predict_false(inp->inp_flags2 & INP_FREED)) {
INP_RUNLOCK(inp);
inp = NULL;
}
} else if (lookupflags & INPLOOKUP_RLOCKLISTEN) {
if (inp->inp_socket != NULL &&
SOLISTENING(inp->inp_socket))
INP_RLOCK(inp);
else
INP_WLOCK(inp);
} else
panic("%s: locking bug", __func__);
#ifdef INVARIANTS
if (inp != NULL) {
if (lookupflags & INPLOOKUP_WLOCKPCB)
INP_WLOCK_ASSERT(inp);
else
INP_RLOCK_ASSERT(inp);
if (__predict_false(inp->inp_flags2 & INP_FREED)) {
INP_UNLOCK(inp);
inp = NULL;
}
#endif
}
return (inp);
@ -2564,8 +2557,8 @@ in_pcblookup(struct inpcbinfo *pcbinfo, struct in_addr faddr, u_int fport,
KASSERT((lookupflags & ~INPLOOKUP_MASK) == 0,
("%s: invalid lookup flags %d", __func__, lookupflags));
KASSERT((lookupflags & (INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB)) != 0,
("%s: LOCKPCB not set", __func__));
KASSERT((lookupflags & (INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB |
INPLOOKUP_RLOCKLISTEN)) != 0, ("%s: LOCKPCB not set", __func__));
/*
* When not using RSS, use connection groups in preference to the
@ -2600,8 +2593,8 @@ in_pcblookup_mbuf(struct inpcbinfo *pcbinfo, struct in_addr faddr,
KASSERT((lookupflags & ~INPLOOKUP_MASK) == 0,
("%s: invalid lookup flags %d", __func__, lookupflags));
KASSERT((lookupflags & (INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB)) != 0,
("%s: LOCKPCB not set", __func__));
KASSERT((lookupflags & (INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB |
INPLOOKUP_RLOCKLISTEN)) != 0, ("%s: LOCKPCB not set", __func__));
#ifdef PCBGROUP
/*

3
sys/netinet/in_pcb.h
View File

@ -761,9 +761,10 @@ int inp_so_options(const struct inpcb *inp);
#define INPLOOKUP_WILDCARD 0x00000001 /* Allow wildcard sockets. */
#define INPLOOKUP_RLOCKPCB 0x00000002 /* Return inpcb read-locked. */
#define INPLOOKUP_WLOCKPCB 0x00000004 /* Return inpcb write-locked. */
#define INPLOOKUP_RLOCKLISTEN 0x00000008 /* Rlock if listening, W if !.*/
#define INPLOOKUP_MASK (INPLOOKUP_WILDCARD | INPLOOKUP_RLOCKPCB | \
INPLOOKUP_WLOCKPCB)
INPLOOKUP_WLOCKPCB | INPLOOKUP_RLOCKLISTEN)
#define sotoinpcb(so) ((struct inpcb *)(so)->so_pcb)

42
sys/netinet/tcp_input.c
View File

@ -626,6 +626,7 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
int drop_hdrlen;
int thflags;
int rstreason = 0; /* For badport_bandlim accounting purposes */
int lookupflag;
uint8_t iptos;
struct m_tag *fwd_tag = NULL;
#ifdef INET6
@ -825,6 +826,12 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
)
fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
/*
* For initial SYN packets arriving on listening socket,
* we don't need write lock.
*/
lookupflag = (thflags & (TH_ACK|TH_SYN)) == TH_SYN ?
INPLOOKUP_RLOCKLISTEN : INPLOOKUP_WLOCKPCB;
findpcb:
#ifdef INET6
if (isipv6 && fwd_tag != NULL) {
@ -837,7 +844,7 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
*/
inp = in6_pcblookup_mbuf(&V_tcbinfo,
&ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif, m);
lookupflag, m->m_pkthdr.rcvif, m);
if (!inp) {
/*
* It's new. Try to find the ambushing socket.
@ -847,14 +854,13 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
th->th_sport, &next_hop6->sin6_addr,
next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
th->th_dport, INPLOOKUP_WILDCARD |
INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
th->th_dport, INPLOOKUP_WILDCARD | lookupflag,
m->m_pkthdr.rcvif);
}
} else if (isipv6) {
inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
th->th_sport, &ip6->ip6_dst, th->th_dport,
INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
m->m_pkthdr.rcvif, m);
INPLOOKUP_WILDCARD | lookupflag, m->m_pkthdr.rcvif, m);
}
#endif /* INET6 */
#if defined(INET6) && defined(INET)
@ -870,8 +876,7 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
* already got one like this?
*/
inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
ip->ip_dst, th->th_dport, INPLOOKUP_WLOCKPCB,
m->m_pkthdr.rcvif, m);
ip->ip_dst, th->th_dport, lookupflag, m->m_pkthdr.rcvif, m);
if (!inp) {
/*
* It's new. Try to find the ambushing socket.
@ -881,14 +886,13 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
th->th_sport, next_hop->sin_addr,
next_hop->sin_port ? ntohs(next_hop->sin_port) :
th->th_dport, INPLOOKUP_WILDCARD |
INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
th->th_dport, INPLOOKUP_WILDCARD | lookupflag,
m->m_pkthdr.rcvif);
}
} else
inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
th->th_sport, ip->ip_dst, th->th_dport,
INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
m->m_pkthdr.rcvif, m);
INPLOOKUP_WILDCARD | lookupflag, m->m_pkthdr.rcvif, m);
#endif /* INET */
/*
@ -918,14 +922,14 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
rstreason = BANDLIM_RST_CLOSEDPORT;
goto dropwithreset;
}
INP_WLOCK_ASSERT(inp);
INP_LOCK_ASSERT(inp);
/*
* While waiting for inp lock during the lookup, another thread
* can have dropped the inpcb, in which case we need to loop back
* and try to find a new inpcb to deliver to.
*/
if (inp->inp_flags & INP_DROPPED) {
INP_WUNLOCK(inp);
INP_UNLOCK(inp);
inp = NULL;
goto findpcb;
}
@ -1014,7 +1018,6 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
#endif
#ifdef MAC
INP_WLOCK_ASSERT(inp);
if (mac_inpcb_check_deliver(inp, m))
goto dropunlock;
#endif
@ -1124,8 +1127,10 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
* Socket is created in state SYN_RECEIVED.
* Unlock the listen socket, lock the newly
* created socket and update the tp variable.
* If we came here via jump to tfo_socket_result,
* then listening socket is read-locked.
*/
INP_WUNLOCK(inp); /* listen socket */
INP_UNLOCK(inp); /* listen socket */
inp = sotoinpcb(so);
/*
* New connection inpcb is already locked by
@ -1213,6 +1218,7 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
("%s: Listen socket: TH_RST or TH_ACK set", __func__));
KASSERT(thflags & (TH_SYN),
("%s: Listen socket: TH_SYN not set", __func__));
INP_RLOCK_ASSERT(inp);
#ifdef INET6
/*
* If deprecated address is forbidden,
@ -1381,7 +1387,7 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
if (inp != NULL) {
tcp_dropwithreset(m, th, tp, tlen, rstreason);
INP_WUNLOCK(inp);
INP_UNLOCK(inp);
} else
tcp_dropwithreset(m, th, NULL, tlen, rstreason);
m = NULL; /* mbuf chain got consumed. */
@ -1392,7 +1398,7 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
TCP_PROBE5(receive, NULL, tp, m, tp, th);
if (inp != NULL)
INP_WUNLOCK(inp);
INP_UNLOCK(inp);
drop:
INP_INFO_WUNLOCK_ASSERT(&V_tcbinfo);
@ -3360,7 +3366,7 @@ tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
#endif
if (tp != NULL) {
INP_WLOCK_ASSERT(tp->t_inpcb);
INP_LOCK_ASSERT(tp->t_inpcb);
}
/* Don't bother if destination was broadcast/multicast. */

2
sys/netinet/tcp_subr.c
View File

@ -1428,7 +1428,7 @@ tcp_respond(struct tcpcb *tp, void *ipgen, struct tcphdr *th, struct mbuf *m,
if (tp != NULL) {
inp = tp->t_inpcb;
KASSERT(inp != NULL, ("tcp control block w/o inpcb"));
INP_WLOCK_ASSERT(inp);
INP_LOCK_ASSERT(inp);
} else
inp = NULL;

10
sys/netinet/tcp_syncache.c
View File

@ -1397,7 +1397,7 @@ syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
int tfo_response_cookie_valid = 0;
bool locked;
INP_WLOCK_ASSERT(inp); /* listen socket */
INP_RLOCK_ASSERT(inp); /* listen socket */
KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
("%s: unexpected tcp flags", __func__));
@ -1469,13 +1469,13 @@ syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
#ifdef MAC
if (mac_syncache_init(&maclabel) != 0) {
INP_WUNLOCK(inp);
INP_RUNLOCK(inp);
goto done;
} else
mac_syncache_create(maclabel, inp);
#endif
if (!tfo_cookie_valid)
INP_WUNLOCK(inp);
INP_RUNLOCK(inp);
/*
* Remember the IP options, if any.
@ -1528,7 +1528,7 @@ syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
}
if (sc != NULL) {
if (tfo_cookie_valid)
INP_WUNLOCK(inp);
INP_RUNLOCK(inp);
TCPSTAT_INC(tcps_sc_dupsyn);
if (ipopts) {
/*
@ -1735,7 +1735,7 @@ syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
if (tfo_cookie_valid) {
syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
/* INP_WUNLOCK(inp) will be performed by the caller */
/* INP_RUNLOCK(inp) will be performed by the caller */
rv = 1;
goto tfo_expanded;
}

34
sys/netinet6/in6_pcb.c
View File

@ -1293,31 +1293,24 @@ in6_pcblookup_hash(struct inpcbinfo *pcbinfo, struct in6_addr *faddr,
struct inpcb *inp;
inp = in6_pcblookup_hash_locked(pcbinfo, faddr, fport, laddr, lport,
(lookupflags & ~(INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB)), ifp,
numa_domain);
lookupflags & INPLOOKUP_WILDCARD, ifp, numa_domain);
if (inp != NULL) {
if (lookupflags & INPLOOKUP_WLOCKPCB) {
INP_WLOCK(inp);
if (__predict_false(inp->inp_flags2 & INP_FREED)) {
INP_WUNLOCK(inp);
inp = NULL;
}
} else if (lookupflags & INPLOOKUP_RLOCKPCB) {
INP_RLOCK(inp);
if (__predict_false(inp->inp_flags2 & INP_FREED)) {
INP_RUNLOCK(inp);
inp = NULL;
}
} else if (lookupflags & INPLOOKUP_RLOCKLISTEN) {
if (inp->inp_socket != NULL &&
SOLISTENING(inp->inp_socket))
INP_RLOCK(inp);
else
INP_WLOCK(inp);
} else
panic("%s: locking bug", __func__);
#ifdef INVARIANTS
if (inp != NULL) {
if (lookupflags & INPLOOKUP_WLOCKPCB)
INP_WLOCK_ASSERT(inp);
else
INP_RLOCK_ASSERT(inp);
if (__predict_false(inp->inp_flags2 & INP_FREED)) {
INP_UNLOCK(inp);
inp = NULL;
}
#endif
}
return (inp);
}
@ -1338,8 +1331,8 @@ in6_pcblookup(struct inpcbinfo *pcbinfo, struct in6_addr *faddr, u_int fport,
KASSERT((lookupflags & ~INPLOOKUP_MASK) == 0,
("%s: invalid lookup flags %d", __func__, lookupflags));
KASSERT((lookupflags & (INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB)) != 0,
("%s: LOCKPCB not set", __func__));
KASSERT((lookupflags & (INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB |
INPLOOKUP_RLOCKLISTEN)) != 0, ("%s: LOCKPCB not set", __func__));
/*
* When not using RSS, use connection groups in preference to the
@ -1374,7 +1367,8 @@ in6_pcblookup_mbuf(struct inpcbinfo *pcbinfo, struct in6_addr *faddr,
KASSERT((lookupflags & ~INPLOOKUP_MASK) == 0,
("%s: invalid lookup flags %d", __func__, lookupflags));
KASSERT((lookupflags & (INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB)) != 0,
KASSERT((lookupflags & (INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB |
INPLOOKUP_RLOCKLISTEN)) != 0,
("%s: LOCKPCB not set", __func__));
#ifdef PCBGROUP

2
sys/security/mac/mac_inet.c
View File

@ -487,7 +487,7 @@ void
mac_syncache_create(struct label *label, struct inpcb *inp)
{
INP_WLOCK_ASSERT(inp);
INP_LOCK_ASSERT(inp);
MAC_POLICY_PERFORM_NOSLEEP(syncache_create, label, inp);
}