fusefs: support EVFILT_WRITE on /dev/fuse

[asomers]

Summary

fusefs: support EVFILT_WRITE on /dev/fuse

/dev/fuse is always ready for writing, so it's kind of dumb to poll it.
But some applications do it anyway. Better to return ready than EINVAL.

MFC after: 2 weeks

Test Plan

Existing kqueue test modified to use kqueue for writing as well as for reading. Tested with a real file system from https://github.com/Sherlock-Holo/fuse3

[emaste]

tests/sys/fs/fusefs/mockfs.cc

870–872

Curious about this change

[asomers]

tests/sys/fs/fusefs/mockfs.cc

870–872

It's necessary to make the tests pass, though I could've done it a different way. The problem is that line 943 adds the EVFILT_WRITE filter to the same fd. When control comes back around to here, kevent() immediately returns because EVFILT_WRITE is still set, and and file descriptor is always writable. So adding EV_ONESHOT at 943 prevents kevent here from returning too soon. And I added EV_ONESHOT here for symmetry's sake, and because line 943 doesn't care about readability.

Alternatively, I could've added EV_ONESHOT at line 943 only; that would've worked. Or, I could've set EV_DISABLE on EVFILT_READ at line 946 or here.

sys/fs/fuse/fuse_device.c

SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_syn, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_insecure_syn), 0,
     "Follow RFC793 instead of RFC5961 criteria for accepting SYN packets");
 
 VNET_DEFINE(int, tcp_insecure_rst) = 0;
 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_insecure_rst), 0,
     "Follow RFC793 instead of RFC5961 criteria for accepting RST packets");
 
+VNET_DEFINE(int, tcp_insecure_ack) = 0;
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_ack, CTLFLAG_VNET | CTLFLAG_RW,
+    &VNET_NAME(tcp_insecure_ack), 0,
+    "Follow RFC793 criteria for validating SEG.ACK");
+
 VNET_DEFINE(int, tcp_recvspace) = 1024*64;
 #define V_tcp_recvspace VNET(tcp_recvspace)
 SYSCTL_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
 
 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_do_autorcvbuf), 0,
if (V_tcp_insecure_syn &&
                         /* Send challenge ACK. */
                         tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
                             tp->snd_nxt, TH_ACK);
                         tp->last_ack_sent = tp->rcv_nxt;
                         m = NULL;
                 }
                 goto drop;
         }
 
         /*
          * RFC 1323 PAWS: If we have a timestamp reply on this segment
          * and it's less than ts_recent, drop it.
          */
         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
                 /* Check to see if ts_recent is over 24 days old.  */
                 if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
if (tp->t_state == TCPS_SYN_RECEIVED ||
                         goto dropafterack;
                 else
                         goto drop;
         }
 
         /*
          * Ack processing.
          */
+        if (SEQ_GEQ(tp->snd_una, tp->iss + (65535 << tp->snd_scale))) {
+                /* Checking SEG.ACK against ISS is definitely redundant. */
+                tp->t_flags2 |= TF2_NO_ISS_CHECK;
+        }
+        if (!V_tcp_insecure_ack) {
+                tcp_seq seq_min;
+                bool ghost_ack_check;
+
+                if (tp->t_flags2 & TF2_NO_ISS_CHECK) {
+                        /* Check for too old ACKs (RFC 5961, Section 5.2). */
+                        seq_min = tp->snd_una - tp->max_sndwnd;
+                        ghost_ack_check = false;
+                } else {
+                        if (SEQ_GT(tp->iss + 1, tp->snd_una - tp->max_sndwnd)) {
+                                /* Checking for ghost ACKs is stricter. */
+                                seq_min = tp->iss + 1;
+                                ghost_ack_check = true;
+                        } else {
+                                /*
+                                 * Checking for too old ACKs (RFC 5961,
+                                 * Section 5.2) is stricter.
+                                 */
+                                seq_min = tp->snd_una - tp->max_sndwnd;
+                                ghost_ack_check = false;
+                        }
+                }
+                if (SEQ_LT(th->th_ack, seq_min)) {
+                        if (ghost_ack_check)
+                                TCPSTAT_INC(tcps_rcvghostack);
+                        else
+                                TCPSTAT_INC(tcps_rcvacktooold);
+                        /* Send a challenge ACK. */
+                        tcp_respond(tp, mtod(m, void *), th, m,
+                            tp->rcv_nxt, tp->snd_nxt, TH_ACK);
+                        tp->last_ack_sent = tp->rcv_nxt;
+                        m = NULL;
+                        goto drop;
+                }
+        }
         switch (tp->t_state) {
         /*
          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
          * ESTABLISHED state and continue processing.
          * The ACK was checked above.
          */
         case TCPS_SYN_RECEIVED:
 

tests/sys/fs/fusefs/mockfs.cc

SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_syn, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_insecure_syn), 0,
     "Follow RFC793 instead of RFC5961 criteria for accepting SYN packets");
 
 VNET_DEFINE(int, tcp_insecure_rst) = 0;
 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_insecure_rst), 0,
     "Follow RFC793 instead of RFC5961 criteria for accepting RST packets");
 
+VNET_DEFINE(int, tcp_insecure_ack) = 0;
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_ack, CTLFLAG_VNET | CTLFLAG_RW,
+    &VNET_NAME(tcp_insecure_ack), 0,
+    "Follow RFC793 criteria for validating SEG.ACK");
+
 VNET_DEFINE(int, tcp_recvspace) = 1024*64;
 #define V_tcp_recvspace VNET(tcp_recvspace)
 SYSCTL_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
 
 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_do_autorcvbuf), 0,
if (V_tcp_insecure_syn &&
                         /* Send challenge ACK. */
                         tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
                             tp->snd_nxt, TH_ACK);
                         tp->last_ack_sent = tp->rcv_nxt;
                         m = NULL;
                 }
                 goto drop;
         }
 
         /*
          * RFC 1323 PAWS: If we have a timestamp reply on this segment
          * and it's less than ts_recent, drop it.
          */
         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
                 /* Check to see if ts_recent is over 24 days old.  */
                 if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
if (tp->t_state == TCPS_SYN_RECEIVED ||
                         goto dropafterack;
                 else
                         goto drop;
         }
 
         /*
          * Ack processing.
          */
+        if (SEQ_GEQ(tp->snd_una, tp->iss + (65535 << tp->snd_scale))) {
+                /* Checking SEG.ACK against ISS is definitely redundant. */
+                tp->t_flags2 |= TF2_NO_ISS_CHECK;
+        }
+        if (!V_tcp_insecure_ack) {
+                tcp_seq seq_min;
+                bool ghost_ack_check;
+
+                if (tp->t_flags2 & TF2_NO_ISS_CHECK) {
+                        /* Check for too old ACKs (RFC 5961, Section 5.2). */
+                        seq_min = tp->snd_una - tp->max_sndwnd;
+                        ghost_ack_check = false;
+                } else {
+                        if (SEQ_GT(tp->iss + 1, tp->snd_una - tp->max_sndwnd)) {
+                                /* Checking for ghost ACKs is stricter. */
+                                seq_min = tp->iss + 1;
+                                ghost_ack_check = true;
+                        } else {
+                                /*
+                                 * Checking for too old ACKs (RFC 5961,
+                                 * Section 5.2) is stricter.
+                                 */
+                                seq_min = tp->snd_una - tp->max_sndwnd;
+                                ghost_ack_check = false;
+                        }
+                }
+                if (SEQ_LT(th->th_ack, seq_min)) {
+                        if (ghost_ack_check)
+                                TCPSTAT_INC(tcps_rcvghostack);
+                        else
+                                TCPSTAT_INC(tcps_rcvacktooold);
+                        /* Send a challenge ACK. */
+                        tcp_respond(tp, mtod(m, void *), th, m,
+                            tp->rcv_nxt, tp->snd_nxt, TH_ACK);
+                        tp->last_ack_sent = tp->rcv_nxt;
+                        m = NULL;
+                        goto drop;
+                }
+        }
         switch (tp->t_state) {
         /*
          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
          * ESTABLISHED state and continue processing.
          * The ACK was checked above.
          */
         case TCPS_SYN_RECEIVED: