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Fix an old and well-documented use-after-free race condition in

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TCP timers:
 - Add a reference from tcpcb to its inpcb
 - Defer tcpcb deletion until TCP timers have finished

Differential Revision:	https://reviews.freebsd.org/D2079
Submitted by:		jch, Marc De La Gueronniere <mdelagueronniere@verisign.com>
Reviewed by:		imp, rrs, adrian, jhb, bz
Approved by:		jhb
Sponsored by:		Verisign, Inc.
This commit is contained in:
Julien Charbon 2015-04-16 10:00:06 +00:00
parent c3358f4ed2
commit 5571f9cf81
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=281599
4 changed files with 206 additions and 100 deletions
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109
sys/netinet/tcp_subr.c
View File

@ -230,6 +230,7 @@ static struct inpcb *tcp_notify(struct inpcb *, int);
static struct inpcb *tcp_mtudisc_notify(struct inpcb *, int);
static char * tcp_log_addr(struct in_conninfo *inc, struct tcphdr *th,
void *ip4hdr, const void *ip6hdr);
static void tcp_timer_discard(struct tcpcb *, uint32_t);
/*
* Target size of TCP PCB hash tables. Must be a power of two.
@ -801,7 +802,13 @@ tcp_newtcpcb(struct inpcb *inp)
if (V_tcp_do_sack)
tp->t_flags |= TF_SACK_PERMIT;
TAILQ_INIT(&tp->snd_holes);
tp->t_inpcb = inp; /* XXX */
/*
* The tcpcb will hold a reference on its inpcb until tcp_discardcb()
* is called.
*/
in_pcbref(inp); /* Reference for tcpcb */
tp->t_inpcb = inp;
/*
* Init srtt to TCPTV_SRTTBASE (0), so we can tell that we have no
* rtt estimate. Set rttvar so that srtt + 4 * rttvar gives
@ -920,6 +927,7 @@ tcp_discardcb(struct tcpcb *tp)
#ifdef INET6
int isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
#endif /* INET6 */
int released;
INP_WLOCK_ASSERT(inp);
@ -927,22 +935,15 @@ tcp_discardcb(struct tcpcb *tp)
* Make sure that all of our timers are stopped before we delete the
* PCB.
*
* XXXRW: Really, we would like to use callout_drain() here in order
* to avoid races experienced in tcp_timer.c where a timer is already
* executing at this point. However, we can't, both because we're
* running in a context where we can't sleep, and also because we
* hold locks required by the timers. What we instead need to do is
* test to see if callout_drain() is required, and if so, defer some
* portion of the remainder of tcp_discardcb() to an asynchronous
* context that can callout_drain() and then continue. Some care
* will be required to ensure that no further processing takes place
* on the tcpcb, even though it hasn't been freed (a flag?).
* If stopping a timer fails, we schedule a discard function in same
* callout, and the last discard function called will take care of
* deleting the tcpcb.
*/
callout_stop(&tp->t_timers->tt_rexmt);
callout_stop(&tp->t_timers->tt_persist);
callout_stop(&tp->t_timers->tt_keep);
callout_stop(&tp->t_timers->tt_2msl);
callout_stop(&tp->t_timers->tt_delack);
tcp_timer_stop(tp, TT_REXMT);
tcp_timer_stop(tp, TT_PERSIST);
tcp_timer_stop(tp, TT_KEEP);
tcp_timer_stop(tp, TT_2MSL);
tcp_timer_stop(tp, TT_DELACK);
/*
* If we got enough samples through the srtt filter,
@ -1019,8 +1020,80 @@ tcp_discardcb(struct tcpcb *tp)
CC_ALGO(tp) = NULL;
inp->inp_ppcb = NULL;
tp->t_inpcb = NULL;
uma_zfree(V_tcpcb_zone, tp);
if ((tp->t_timers->tt_flags & TT_MASK) == 0) {
/* We own the last reference on tcpcb, let's free it. */
tp->t_inpcb = NULL;
uma_zfree(V_tcpcb_zone, tp);
released = in_pcbrele_wlocked(inp);
KASSERT(!released, ("%s: inp %p should not have been released "
"here", __func__, inp));
}
}
void
tcp_timer_2msl_discard(void *xtp)
{
tcp_timer_discard((struct tcpcb *)xtp, TT_2MSL);
}
void
tcp_timer_keep_discard(void *xtp)
{
tcp_timer_discard((struct tcpcb *)xtp, TT_KEEP);
}
void
tcp_timer_persist_discard(void *xtp)
{
tcp_timer_discard((struct tcpcb *)xtp, TT_PERSIST);
}
void
tcp_timer_rexmt_discard(void *xtp)
{
tcp_timer_discard((struct tcpcb *)xtp, TT_REXMT);
}
void
tcp_timer_delack_discard(void *xtp)
{
tcp_timer_discard((struct tcpcb *)xtp, TT_DELACK);
}
void
tcp_timer_discard(struct tcpcb *tp, uint32_t timer_type)
{
struct inpcb *inp;
CURVNET_SET(tp->t_vnet);
INP_INFO_WLOCK(&V_tcbinfo);
inp = tp->t_inpcb;
KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL",
__func__, tp));
INP_WLOCK(inp);
KASSERT((tp->t_timers->tt_flags & TT_STOPPED) != 0,
("%s: tcpcb has to be stopped here", __func__));
KASSERT((tp->t_timers->tt_flags & timer_type) != 0,
("%s: discard callout should be running", __func__));
tp->t_timers->tt_flags &= ~timer_type;
if ((tp->t_timers->tt_flags & TT_MASK) == 0) {
/* We own the last reference on this tcpcb, let's free it. */
tp->t_inpcb = NULL;
uma_zfree(V_tcpcb_zone, tp);
if (in_pcbrele_wlocked(inp)) {
INP_INFO_WUNLOCK(&V_tcbinfo);
CURVNET_RESTORE();
return;
}
}
INP_WUNLOCK(inp);
INP_INFO_WUNLOCK(&V_tcbinfo);
CURVNET_RESTORE();
}
/*

168
sys/netinet/tcp_timer.c
View File

@ -258,10 +258,6 @@ int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
static int tcp_totbackoff = 2559; /* sum of tcp_backoff[] */
static int tcp_timer_race;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, timer_race, CTLFLAG_RD, &tcp_timer_race,
0, "Count of t_inpcb races on tcp_discardcb");
/*
* TCP timer processing.
*/
@ -274,18 +270,7 @@ tcp_timer_delack(void *xtp)
CURVNET_SET(tp->t_vnet);
inp = tp->t_inpcb;
/*
* XXXRW: While this assert is in fact correct, bugs in the tcpcb
* tear-down mean we need it as a work-around for races between
* timers and tcp_discardcb().
*
* KASSERT(inp != NULL, ("tcp_timer_delack: inp == NULL"));
*/
if (inp == NULL) {
tcp_timer_race++;
CURVNET_RESTORE();
return;
}
KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
INP_WLOCK(inp);
if (callout_pending(&tp->t_timers->tt_delack) ||
!callout_active(&tp->t_timers->tt_delack)) {
@ -299,6 +284,10 @@ tcp_timer_delack(void *xtp)
CURVNET_RESTORE();
return;
}
KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
("%s: tp %p tcpcb can't be stopped here", __func__, tp));
KASSERT((tp->t_timers->tt_flags & TT_DELACK) != 0,
("%s: tp %p delack callout should be running", __func__, tp));
tp->t_flags |= TF_ACKNOW;
TCPSTAT_INC(tcps_delack);
@ -318,24 +307,9 @@ tcp_timer_2msl(void *xtp)
ostate = tp->t_state;
#endif
/*
* XXXRW: Does this actually happen?
*/
INP_INFO_WLOCK(&V_tcbinfo);
inp = tp->t_inpcb;
/*
* XXXRW: While this assert is in fact correct, bugs in the tcpcb
* tear-down mean we need it as a work-around for races between
* timers and tcp_discardcb().
*
* KASSERT(inp != NULL, ("tcp_timer_2msl: inp == NULL"));
*/
if (inp == NULL) {
tcp_timer_race++;
INP_INFO_WUNLOCK(&V_tcbinfo);
CURVNET_RESTORE();
return;
}
KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
INP_WLOCK(inp);
tcp_free_sackholes(tp);
if (callout_pending(&tp->t_timers->tt_2msl) ||
@ -352,6 +326,10 @@ tcp_timer_2msl(void *xtp)
CURVNET_RESTORE();
return;
}
KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
("%s: tp %p tcpcb can't be stopped here", __func__, tp));
KASSERT((tp->t_timers->tt_flags & TT_2MSL) != 0,
("%s: tp %p 2msl callout should be running", __func__, tp));
/*
* 2 MSL timeout in shutdown went off. If we're closed but
* still waiting for peer to close and connection has been idle
@ -402,19 +380,7 @@ tcp_timer_keep(void *xtp)
#endif
INP_INFO_WLOCK(&V_tcbinfo);
inp = tp->t_inpcb;
/*
* XXXRW: While this assert is in fact correct, bugs in the tcpcb
* tear-down mean we need it as a work-around for races between
* timers and tcp_discardcb().
*
* KASSERT(inp != NULL, ("tcp_timer_keep: inp == NULL"));
*/
if (inp == NULL) {
tcp_timer_race++;
INP_INFO_WUNLOCK(&V_tcbinfo);
CURVNET_RESTORE();
return;
}
KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
INP_WLOCK(inp);
if (callout_pending(&tp->t_timers->tt_keep) ||
!callout_active(&tp->t_timers->tt_keep)) {
@ -430,6 +396,10 @@ tcp_timer_keep(void *xtp)
CURVNET_RESTORE();
return;
}
KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
("%s: tp %p tcpcb can't be stopped here", __func__, tp));
KASSERT((tp->t_timers->tt_flags & TT_KEEP) != 0,
("%s: tp %p keep callout should be running", __func__, tp));
/*
* Keep-alive timer went off; send something
* or drop connection if idle for too long.
@ -505,19 +475,7 @@ tcp_timer_persist(void *xtp)
#endif
INP_INFO_WLOCK(&V_tcbinfo);
inp = tp->t_inpcb;
/*
* XXXRW: While this assert is in fact correct, bugs in the tcpcb
* tear-down mean we need it as a work-around for races between
* timers and tcp_discardcb().
*
* KASSERT(inp != NULL, ("tcp_timer_persist: inp == NULL"));
*/
if (inp == NULL) {
tcp_timer_race++;
INP_INFO_WUNLOCK(&V_tcbinfo);
CURVNET_RESTORE();
return;
}
KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
INP_WLOCK(inp);
if (callout_pending(&tp->t_timers->tt_persist) ||
!callout_active(&tp->t_timers->tt_persist)) {
@ -533,6 +491,10 @@ tcp_timer_persist(void *xtp)
CURVNET_RESTORE();
return;
}
KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
("%s: tp %p tcpcb can't be stopped here", __func__, tp));
KASSERT((tp->t_timers->tt_flags & TT_PERSIST) != 0,
("%s: tp %p persist callout should be running", __func__, tp));
/*
* Persistance timer into zero window.
* Force a byte to be output, if possible.
@ -594,19 +556,7 @@ tcp_timer_rexmt(void * xtp)
INP_INFO_RLOCK(&V_tcbinfo);
inp = tp->t_inpcb;
/*
* XXXRW: While this assert is in fact correct, bugs in the tcpcb
* tear-down mean we need it as a work-around for races between
* timers and tcp_discardcb().
*
* KASSERT(inp != NULL, ("tcp_timer_rexmt: inp == NULL"));
*/
if (inp == NULL) {
tcp_timer_race++;
INP_INFO_RUNLOCK(&V_tcbinfo);
CURVNET_RESTORE();
return;
}
KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
INP_WLOCK(inp);
if (callout_pending(&tp->t_timers->tt_rexmt) ||
!callout_active(&tp->t_timers->tt_rexmt)) {
@ -622,6 +572,10 @@ tcp_timer_rexmt(void * xtp)
CURVNET_RESTORE();
return;
}
KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
("%s: tp %p tcpcb can't be stopped here", __func__, tp));
KASSERT((tp->t_timers->tt_flags & TT_REXMT) != 0,
("%s: tp %p rexmt callout should be running", __func__, tp));
tcp_free_sackholes(tp);
/*
* Retransmission timer went off. Message has not
@ -850,7 +804,7 @@ tcp_timer_rexmt(void * xtp)
}
void
tcp_timer_activate(struct tcpcb *tp, int timer_type, u_int delta)
tcp_timer_activate(struct tcpcb *tp, uint32_t timer_type, u_int delta)
{
struct callout *t_callout;
timeout_t *f_callout;
@ -862,6 +816,9 @@ tcp_timer_activate(struct tcpcb *tp, int timer_type, u_int delta)
return;
#endif
if (tp->t_timers->tt_flags & TT_STOPPED)
return;
switch (timer_type) {
case TT_DELACK:
t_callout = &tp->t_timers->tt_delack;
@ -887,14 +844,23 @@ tcp_timer_activate(struct tcpcb *tp, int timer_type, u_int delta)
panic("tp %p bad timer_type %#x", tp, timer_type);
}
if (delta == 0) {
callout_stop(t_callout);
if ((tp->t_timers->tt_flags & timer_type) &&
callout_stop(t_callout)) {
tp->t_timers->tt_flags &= ~timer_type;
}
} else {
callout_reset_on(t_callout, delta, f_callout, tp, cpu);
if ((tp->t_timers->tt_flags & timer_type) == 0) {
tp->t_timers->tt_flags |= timer_type;
callout_reset_on(t_callout, delta, f_callout, tp, cpu);
} else {
/* Reset already running callout on the same CPU. */
callout_reset(t_callout, delta, f_callout, tp);
}
}
}
int
tcp_timer_active(struct tcpcb *tp, int timer_type)
tcp_timer_active(struct tcpcb *tp, uint32_t timer_type)
{
struct callout *t_callout;
@ -920,6 +886,58 @@ tcp_timer_active(struct tcpcb *tp, int timer_type)
return callout_active(t_callout);
}
void
tcp_timer_stop(struct tcpcb *tp, uint32_t timer_type)
{
struct callout *t_callout;
timeout_t *f_callout;
tp->t_timers->tt_flags |= TT_STOPPED;
switch (timer_type) {
case TT_DELACK:
t_callout = &tp->t_timers->tt_delack;
f_callout = tcp_timer_delack_discard;
break;
case TT_REXMT:
t_callout = &tp->t_timers->tt_rexmt;
f_callout = tcp_timer_rexmt_discard;
break;
case TT_PERSIST:
t_callout = &tp->t_timers->tt_persist;
f_callout = tcp_timer_persist_discard;
break;
case TT_KEEP:
t_callout = &tp->t_timers->tt_keep;
f_callout = tcp_timer_keep_discard;
break;
case TT_2MSL:
t_callout = &tp->t_timers->tt_2msl;
f_callout = tcp_timer_2msl_discard;
break;
default:
panic("tp %p bad timer_type %#x", tp, timer_type);
}
if (tp->t_timers->tt_flags & timer_type) {
if (callout_stop(t_callout)) {
tp->t_timers->tt_flags &= ~timer_type;
} else {
/*
* Can't stop the callout, defer tcpcb actual deletion
* to the last tcp timer discard callout.
* The TT_STOPPED flag will ensure that no tcp timer
* callouts can be restarted on our behalf, and
* past this point currently running callouts waiting
* on inp lock will return right away after the
* classical check for callout reset/stop events:
* callout_pending() || !callout_active()
*/
callout_reset(t_callout, 1, f_callout, tp);
}
}
}
#define ticks_to_msecs(t) (1000*(t) / hz)
void

24
sys/netinet/tcp_timer.h
View File

@ -146,12 +146,21 @@ struct tcp_timer {
struct callout tt_keep; /* keepalive */
struct callout tt_2msl; /* 2*msl TIME_WAIT timer */
struct callout tt_delack; /* delayed ACK timer */
uint32_t tt_flags; /* Timers flags */
uint32_t tt_spare; /* TDB */
};
#define TT_DELACK 0x01
#define TT_REXMT 0x02
#define TT_PERSIST 0x04
#define TT_KEEP 0x08
#define TT_2MSL 0x10
/*
* Flags for the tt_flags field.
*/
#define TT_DELACK 0x0001
#define TT_REXMT 0x0002
#define TT_PERSIST 0x0004
#define TT_KEEP 0x0008
#define TT_2MSL 0x0010
#define TT_MASK (TT_DELACK|TT_REXMT|TT_PERSIST|TT_KEEP|TT_2MSL)
#define TT_STOPPED 0x00010000
#define TP_KEEPINIT(tp) ((tp)->t_keepinit ? (tp)->t_keepinit : tcp_keepinit)
#define TP_KEEPIDLE(tp) ((tp)->t_keepidle ? (tp)->t_keepidle : tcp_keepidle)
@ -183,6 +192,11 @@ void tcp_timer_keep(void *xtp);
void tcp_timer_persist(void *xtp);
void tcp_timer_rexmt(void *xtp);
void tcp_timer_delack(void *xtp);
void tcp_timer_2msl_discard(void *xtp);
void tcp_timer_keep_discard(void *xtp);
void tcp_timer_persist_discard(void *xtp);
void tcp_timer_rexmt_discard(void *xtp);
void tcp_timer_delack_discard(void *xtp);
void tcp_timer_to_xtimer(struct tcpcb *tp, struct tcp_timer *timer,
struct xtcp_timer *xtimer);

5
sys/netinet/tcp_var.h
View File

@ -708,8 +708,9 @@ void tcp_slowtimo(void);
struct tcptemp *
tcpip_maketemplate(struct inpcb *);
void tcpip_fillheaders(struct inpcb *, void *, void *);
void tcp_timer_activate(struct tcpcb *, int, u_int);
int tcp_timer_active(struct tcpcb *, int);
void tcp_timer_activate(struct tcpcb *, uint32_t, u_int);
int tcp_timer_active(struct tcpcb *, uint32_t);
void tcp_timer_stop(struct tcpcb *, uint32_t);
void tcp_trace(short, short, struct tcpcb *, void *, struct tcphdr *, int);
/*
* All tcp_hc_* functions are IPv4 and IPv6 (via in_conninfo)