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tcp: Don't try to upgrade a read lock just for logging

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Reviewed by:		glebius, lstewart, rrs
Sponsored by:		Netflix, Inc.
Differential Revision:	https://reviews.freebsd.org/D33098
This commit is contained in:
Michael Tuexen 2021-11-26 11:53:00 +01:00
parent e671037b3c
commit 147bf5e930
1 changed files with 40 additions and 14 deletions
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54
sys/netinet/tcp_subr.c
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@ -101,6 +101,9 @@ __FBSDID("$FreeBSD$");
#endif
#include <netinet/tcp.h>
#ifdef INVARIANTS
#define TCPSTATES
#endif
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
@ -1755,9 +1758,12 @@ tcp_respond(struct tcpcb *tp, void *ipgen, struct tcphdr *th, struct mbuf *m,
int isipv6;
#endif /* INET6 */
int optlen, tlen, win, ulen;
bool incl_opts, lock_upgraded;
bool incl_opts;
uint16_t port;
int output_ret;
#ifdef INVARIANTS
int thflags = th->th_flags;
#endif
KASSERT(tp != NULL || m != NULL, ("tcp_respond: tp and m both NULL"));
NET_EPOCH_ASSERT();
@ -2088,18 +2094,12 @@ tcp_respond(struct tcpcb *tp, void *ipgen, struct tcphdr *th, struct mbuf *m,
TCP_PROBE3(debug__output, tp, th, m);
if (flags & TH_RST)
TCP_PROBE5(accept__refused, NULL, NULL, m, tp, nth);
lock_upgraded = false;
lgb = NULL;
if ((tp != NULL) && (tp->t_logstate != TCP_LOG_STATE_OFF)) {
union tcp_log_stackspecific log;
struct timeval tv;
lock_upgraded = !INP_WLOCKED(inp) && INP_TRY_UPGRADE(inp);
/*
*`If we don't already own the write lock and can't upgrade,
* just don't log the event, but still send the response.
*/
if (INP_WLOCKED(inp)) {
union tcp_log_stackspecific log;
struct timeval tv;
memset(&log.u_bbr, 0, sizeof(log.u_bbr));
log.u_bbr.inhpts = tp->t_inpcb->inp_in_hpts;
log.u_bbr.ininput = tp->t_inpcb->inp_in_input;
@ -2107,8 +2107,36 @@ tcp_respond(struct tcpcb *tp, void *ipgen, struct tcphdr *th, struct mbuf *m,
log.u_bbr.pkts_out = tp->t_maxseg;
log.u_bbr.timeStamp = tcp_get_usecs(&tv);
log.u_bbr.delivered = 0;
lgb = tcp_log_event_(tp, nth, NULL, NULL, TCP_LOG_OUT, ERRNO_UNK,
0, &log, false, NULL, NULL, 0, &tv);
lgb = tcp_log_event_(tp, nth, NULL, NULL, TCP_LOG_OUT,
ERRNO_UNK, 0, &log, false, NULL, NULL, 0, &tv);
} else {
/*
* We can not log the packet, since we only own the
* read lock, but a write lock is needed. The read lock
* is not upgraded to a write lock, since only getting
* the read lock was done intentionally to improve the
* handling of SYN flooding attacks.
* This happens only for pure SYN segments received in
* the initial CLOSED state, or received in a more
* advanced state than listen and the UDP encapsulation
* port is unexpected.
* The incoming SYN segments do not really belong to
* the TCP connection and the handling does not change
* the state of the TCP connection. Therefore, the
* sending of the RST segments is not logged. Please
* note that also the incoming SYN segments are not
* logged.
*
* The following code ensures that the above description
* is and stays correct.
*/
KASSERT((thflags & (TH_ACK|TH_SYN)) == TH_SYN &&
(tp->t_state == TCPS_CLOSED ||
(tp->t_state > TCPS_LISTEN && tp->t_port != port)),
("%s: Logging of TCP segment with flags 0x%b and "
"UDP encapsulation port %u skipped in state %s",
__func__, thflags, PRINT_TH_FLAGS,
ntohs(port), tcpstates[tp->t_state]));
}
}
@ -2129,8 +2157,6 @@ tcp_respond(struct tcpcb *tp, void *ipgen, struct tcphdr *th, struct mbuf *m,
#endif
if (lgb != NULL)
lgb->tlb_errno = output_ret;
if (lock_upgraded)
INP_DOWNGRADE(inp);
}
/*