BUG/MINOR: stream/debug: harden the stream dump function regarding signals

As seen in GH issue #3490, it is sometimes possible to see a stream in
an intermediate state during a dump (due to the dump being called by a
signal handler). The code was already designed in a defensive way for
this, but not sufficiently.

Indeed, while a stream my never be seen in a stable state with NULL in
any of its sedesc, there exist a short period during sc_reset_endp()
where the backend sedesc is NULL for a few nanoseconds, between the
NULL and the new value, and if a dump signal happens in the middle,
the __strm_dump_to_buffer() function will crash.

This patch modifies __strm_dump_to_buffer() so that the sc, sd and conns
are taken for each side when entering the function and used as tests every
time they're about to be dereferenced. This way certain fields will be
omitted whenever such situations happen.

This new version now resists heavy connection retries combined with
1ms warnings and two parallel "show threads" loops..

This should be backported to stable releases. It is likely that it will
not easily apply to all versions, so the changes might more easily be
re-done; the principle consists in conditioning the dereference of
sc->sedesc for each side (which also happens when reading flags).

diff --git a/src/stream.c b/src/stream.c
index 29767d7bb1cbae0e3e81a1e1fc14172df2a57ab0..4a42f39d4de29be6b444e3d838a8c5783bf30a07 100644 (file)
--- a/src/stream.c
+++ b/src/stream.c
@@ -3471,12 +3471,22 @@ static void __strm_dump_to_buffer(struct buffer *buf, const struct show_sess_ctx
        struct tm tm;
        extern const char *monthname[12];
        char pn[INET6_ADDRSTRLEN];
-       struct connection *conn;
+       struct sedesc *sdf, *sdb;
+       struct connection *connf, *connb;
        struct appctx *tmpctx;
        uint64_t request_ts;
        uint strm_tgid = ha_thread_info[strm->task->tid].tgid;
        const struct fdtab *strm_fdtab = ha_tgroup_ctx[strm_tgid - 1].fdtab;
 
+       /* note: seb, connf and connb may be NULL */
+
+       scf = strm->scf;
+       scb = strm->scb;
+       sdf = scf->sedesc;
+       sdb = scb->sedesc;
+       connf = objt_conn(strm_orig(strm));
+       connb = sdb ? sc_conn(strm->scb) : NULL;
+
        pfx = pfx ? pfx : "";
 
        if (th_ctx->flags & TH_FL_IN_ANY_HANDLER) {
@@ -3499,17 +3509,15 @@ static void __strm_dump_to_buffer(struct buffer *buf, const struct show_sess_ctx
        chunk_appendf(buf, " id=%u proto=%s",
                     strm->uniq_id, strm_li(strm) ? strm_li(strm)->rx.proto->name : "?");
 
-       conn = objt_conn(strm_orig(strm));
-
        /* be careful not to allocate RAM from a signal handler! */
-       if (conn && !conn->src && !(th_ctx->flags & TH_FL_IN_ANY_HANDLER))
-               conn_get_src(conn);
+       if (connf && !connf->src && !(th_ctx->flags & TH_FL_IN_ANY_HANDLER))
+               conn_get_src(connf);
 
-       switch (conn && conn->src ? addr_to_str(conn->src, pn, sizeof(pn)) : AF_UNSPEC) {
+       switch (connf && connf->src ? addr_to_str(connf->src, pn, sizeof(pn)) : AF_UNSPEC) {
        case AF_INET:
        case AF_INET6:
                chunk_appendf(buf, " source=%s:%d\n",
-                             HA_ANON_STR(anon_key, pn), get_host_port(conn->src));
+                             HA_ANON_STR(anon_key, pn), get_host_port(connf->src));
                break;
        case AF_UNIX:
        case AF_CUST_ABNS:
@@ -3542,14 +3550,14 @@ static void __strm_dump_to_buffer(struct buffer *buf, const struct show_sess_ctx
                     strm_li(strm) ? strm_li(strm)->luid : 0);
 
        /* be careful not to allocate RAM from a signal handler! */
-       if (conn && !conn->dst && !(th_ctx->flags & TH_FL_IN_ANY_HANDLER))
-               conn_get_dst(conn);
+       if (connf && !connf->dst && !(th_ctx->flags & TH_FL_IN_ANY_HANDLER))
+               conn_get_dst(connf);
 
-       switch (conn && conn->dst ? addr_to_str(conn->dst, pn, sizeof(pn)) : AF_UNSPEC) {
+       switch (connf && connf->dst ? addr_to_str(connf->dst, pn, sizeof(pn)) : AF_UNSPEC) {
        case AF_INET:
        case AF_INET6:
                chunk_appendf(buf, " addr=%s:%d\n",
-                            HA_ANON_STR(anon_key, pn), get_host_port(conn->dst));
+                            HA_ANON_STR(anon_key, pn), get_host_port(connf->dst));
                break;
        case AF_UNIX:
        case AF_CUST_ABNS:
@@ -3570,17 +3578,15 @@ static void __strm_dump_to_buffer(struct buffer *buf, const struct show_sess_ctx
        else
                chunk_appendf(buf, "%s  backend=<NONE> (id=-1 mode=-)", pfx);
 
-       conn = sc_conn(strm->scb);
-
        /* be careful not to allocate RAM from a signal handler! */
-       if (conn && !conn->src && !(th_ctx->flags & TH_FL_IN_ANY_HANDLER))
-               conn_get_src(conn);
+       if (connb && !connb->src && !(th_ctx->flags & TH_FL_IN_ANY_HANDLER))
+               conn_get_src(connb);
 
-       switch (conn && conn->src ? addr_to_str(conn->src, pn, sizeof(pn)) : AF_UNSPEC) {
+       switch (connb && connb->src ? addr_to_str(connb->src, pn, sizeof(pn)) : AF_UNSPEC) {
        case AF_INET:
        case AF_INET6:
                chunk_appendf(buf, " addr=%s:%d\n",
-                            HA_ANON_STR(anon_key, pn), get_host_port(conn->src));
+                            HA_ANON_STR(anon_key, pn), get_host_port(connb->src));
                break;
        case AF_UNIX:
        case AF_CUST_ABNS:
@@ -3602,14 +3608,14 @@ static void __strm_dump_to_buffer(struct buffer *buf, const struct show_sess_ctx
                chunk_appendf(buf, "%s  server=<NONE> (id=-1)", pfx);
 
        /* be careful not to allocate RAM from a signal handler! */
-       if (conn && !conn->dst && !(th_ctx->flags & TH_FL_IN_ANY_HANDLER))
-               conn_get_dst(conn);
+       if (connb && !connb->dst && !(th_ctx->flags & TH_FL_IN_ANY_HANDLER))
+               conn_get_dst(connb);
 
-       switch (conn && conn->dst ? addr_to_str(conn->dst, pn, sizeof(pn)) : AF_UNSPEC) {
+       switch (connb && connb->dst ? addr_to_str(connb->dst, pn, sizeof(pn)) : AF_UNSPEC) {
        case AF_INET:
        case AF_INET6:
                chunk_appendf(buf, " addr=%s:%d\n",
-                            HA_ANON_STR(anon_key, pn), get_host_port(conn->dst));
+                            HA_ANON_STR(anon_key, pn), get_host_port(connb->dst));
                break;
        case AF_UNIX:
        case AF_CUST_ABNS:
@@ -3657,57 +3663,62 @@ static void __strm_dump_to_buffer(struct buffer *buf, const struct show_sess_ctx
                chunk_memcat(buf, "\n", 1);
        }
 
-       scf = strm->scf;
        chunk_appendf(buf, "%s  scf=%p flags=0x%08x ioto=%s state=%s endp=%s,%p,0x%08x sub=%d in=%llu out=%llu", pfx,
                      scf, scf->flags, human_time(scf->ioto, TICKS_TO_MS(1000)), sc_state_str(scf->state),
-                     (sc_ep_test(scf, SE_FL_T_MUX) ? "CONN" : (sc_ep_test(scf, SE_FL_T_APPLET) ? "APPCTX" : "NONE")),
-                     scf->sedesc->se, sc_ep_get(scf), scf->wait_event.events, scf->bytes_in, scf->bytes_out);
-       chunk_appendf(buf, " rex=%s",
-                     sc_ep_rcv_ex(scf) ? human_time(TICKS_TO_MS(sc_ep_rcv_ex(scf) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
-       chunk_appendf(buf, " wex=%s",
-                     sc_ep_snd_ex(scf) ? human_time(TICKS_TO_MS(sc_ep_snd_ex(scf) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
-       chunk_appendf(buf, " rto=%s",
-                     tick_isset(scf->sedesc->lra) ? human_time(TICKS_TO_MS(tick_add(scf->sedesc->lra, scf->ioto) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
-       chunk_appendf(buf, " wto=%s\n",
-                     tick_isset(scf->sedesc->fsb) ? human_time(TICKS_TO_MS(tick_add(scf->sedesc->fsb, scf->ioto) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
-
-       chunk_appendf(&trash, "%s    iobuf.flags=0x%08x .pipe=%d .buf=%u@%p+%u/%u\n", pfx,
-                     scf->sedesc->iobuf.flags,
-                     scf->sedesc->iobuf.pipe ? scf->sedesc->iobuf.pipe->data : 0,
-                     scf->sedesc->iobuf.buf ? (unsigned int)b_data(scf->sedesc->iobuf.buf): 0,
-                     scf->sedesc->iobuf.buf ? b_orig(scf->sedesc->iobuf.buf): NULL,
-                     scf->sedesc->iobuf.buf ? (unsigned int)b_head_ofs(scf->sedesc->iobuf.buf): 0,
-                     scf->sedesc->iobuf.buf ? (unsigned int)b_size(scf->sedesc->iobuf.buf): 0);
-
-       if ((conn = sc_conn(scf)) != NULL) {
-               if (conn->mux && conn->mux->show_sd) {
+                     (sdf && se_fl_test(sdf, SE_FL_T_MUX) ? "CONN" : (sdf && se_fl_test(sdf, SE_FL_T_APPLET) ? "APPCTX" : "NONE")),
+                     sdf ? sdf->se : NULL, sdf ? se_fl_get(sdf) : 0, scf->wait_event.events, scf->bytes_in, scf->bytes_out);
+
+       if (sdf) {
+               chunk_appendf(buf, " rex=%s",
+                             sdf && sc_ep_rcv_ex(scf) ? human_time(TICKS_TO_MS(sc_ep_rcv_ex(scf) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
+               chunk_appendf(buf, " wex=%s",
+                             sdf && sc_ep_snd_ex(scf) ? human_time(TICKS_TO_MS(sc_ep_snd_ex(scf) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
+               chunk_appendf(buf, " rto=%s",
+                             sdf && tick_isset(sdf->lra) ? human_time(TICKS_TO_MS(tick_add(sdf->lra, scf->ioto) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
+               chunk_appendf(buf, " wto=%s\n",
+                             sdf && tick_isset(sdf->fsb) ? human_time(TICKS_TO_MS(tick_add(sdf->fsb, scf->ioto) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
+       }
+
+       chunk_appendf(buf, "\n");
+
+       if (sdf)
+               chunk_appendf(&trash, "%s    iobuf.flags=0x%08x .pipe=%d .buf=%u@%p+%u/%u\n", pfx,
+                             sdf->iobuf.flags,
+                             sdf->iobuf.pipe ? sdf->iobuf.pipe->data : 0,
+                             sdf->iobuf.buf ? (unsigned int)b_data(sdf->iobuf.buf): 0,
+                             sdf->iobuf.buf ? b_orig(sdf->iobuf.buf): NULL,
+                             sdf->iobuf.buf ? (unsigned int)b_head_ofs(sdf->iobuf.buf): 0,
+                             sdf->iobuf.buf ? (unsigned int)b_size(sdf->iobuf.buf): 0);
+
+       if (connf) {
+               if (connf->mux && connf->mux->show_sd) {
                        char muxpfx[100] = "";
 
                        snprintf(muxpfx, sizeof(muxpfx), "%s      ", pfx);
                        chunk_appendf(buf, "%s     ", pfx);
-                       conn->mux->show_sd(buf, scf->sedesc, muxpfx);
+                       connf->mux->show_sd(buf, sdf, muxpfx);
                        chunk_appendf(buf, "\n");
                }
 
                chunk_appendf(buf,
                              "%s      co0=%p ctrl=%s xprt=%s mux=%s target=%s:%p\n", pfx,
-                             conn,
-                             conn_get_ctrl_name(conn),
-                             conn_get_xprt_name(conn),
-                             conn_get_mux_name(conn),
-                             obj_type_name(conn->target),
-                             obj_base_ptr(conn->target));
+                             connf,
+                             conn_get_ctrl_name(connf),
+                             conn_get_xprt_name(connf),
+                             conn_get_mux_name(connf),
+                             obj_type_name(connf->target),
+                             obj_base_ptr(connf->target));
 
                chunk_appendf(buf,
                              "%s      flags=0x%08x fd=%u/%d fd.state=%02x updt=%d fd.tmask=0x%lx\n", pfx,
-                             conn->flags,
+                             connf->flags,
                              strm_tgid,
-                             conn_fd(conn),
-                             conn_fd(conn) >= 0 ? strm_fdtab[conn->handle.fd].state : 0,
-                             conn_fd(conn) >= 0 ? !!(strm_fdtab[conn->handle.fd].update_mask & ti->ltid_bit) : 0,
-                             conn_fd(conn) >= 0 ? strm_fdtab[conn->handle.fd].thread_mask: 0);
+                             conn_fd(connf),
+                             conn_fd(connf) >= 0 ? strm_fdtab[connf->handle.fd].state : 0,
+                             conn_fd(connf) >= 0 ? !!(strm_fdtab[connf->handle.fd].update_mask & ti->ltid_bit) : 0,
+                             conn_fd(connf) >= 0 ? strm_fdtab[connf->handle.fd].thread_mask: 0);
        }
-       else if ((tmpctx = sc_appctx(scf)) != NULL) {
+       else if (sdf && (tmpctx = sc_appctx(scf)) != NULL) {
                chunk_appendf(buf,
                              "%s      app0=%p st0=%d st1=%d applet=%s tid=%d nice=%d calls=%u rate=%u\n", pfx,
                              tmpctx,
@@ -3719,57 +3730,63 @@ static void __strm_dump_to_buffer(struct buffer *buf, const struct show_sess_ctx
                              read_freq_ctr_period_estimate(&tmpctx->call_rate, MS_TO_TICKS(1000)));
        }
 
-       scb = strm->scb;
        chunk_appendf(buf, "%s  scb=%p flags=0x%08x ioto=%s state=%s endp=%s,%p,0x%08x sub=%d in=%llu out=%llu", pfx,
                      scb, scb->flags, human_time(scb->ioto, TICKS_TO_MS(1000)), sc_state_str(scb->state),
-                     (sc_ep_test(scb, SE_FL_T_MUX) ? "CONN" : (sc_ep_test(scb, SE_FL_T_APPLET) ? "APPCTX" : "NONE")),
-                     scb->sedesc->se, sc_ep_get(scb), scb->wait_event.events, scb->bytes_in, scb->bytes_out);
-       chunk_appendf(buf, " rex=%s",
-                     sc_ep_rcv_ex(scb) ? human_time(TICKS_TO_MS(sc_ep_rcv_ex(scb) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
-       chunk_appendf(buf, " wex=%s",
-                     sc_ep_snd_ex(scb) ? human_time(TICKS_TO_MS(sc_ep_snd_ex(scb) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
-       chunk_appendf(buf, " rto=%s",
-                     tick_isset(scb->sedesc->lra) ? human_time(TICKS_TO_MS(tick_add(scb->sedesc->lra, scb->ioto) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
-       chunk_appendf(buf, " wto=%s\n",
-                     tick_isset(scb->sedesc->fsb) ? human_time(TICKS_TO_MS(tick_add(scb->sedesc->fsb, scb->ioto) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
-
-       chunk_appendf(&trash, "%s    iobuf.flags=0x%08x .pipe=%d .buf=%u@%p+%u/%u\n", pfx,
-                     scb->sedesc->iobuf.flags,
-                     scb->sedesc->iobuf.pipe ? scb->sedesc->iobuf.pipe->data : 0,
-                     scb->sedesc->iobuf.buf ? (unsigned int)b_data(scb->sedesc->iobuf.buf): 0,
-                     scb->sedesc->iobuf.buf ? b_orig(scb->sedesc->iobuf.buf): NULL,
-                     scb->sedesc->iobuf.buf ? (unsigned int)b_head_ofs(scb->sedesc->iobuf.buf): 0,
-                     scb->sedesc->iobuf.buf ? (unsigned int)b_size(scb->sedesc->iobuf.buf): 0);
-
-       if ((conn = sc_conn(scb)) != NULL) {
-               if (conn->mux && conn->mux->show_sd) {
+                     (sdb && se_fl_test(sdb, SE_FL_T_MUX) ? "CONN" : (sdb && se_fl_test(sdb, SE_FL_T_APPLET) ? "APPCTX" : "NONE")),
+                     sdb ? sdb->se : NULL, sdb ? se_fl_get(sdb) : 0, scb->wait_event.events, scb->bytes_in, scb->bytes_out);
+
+       if (sdb) {
+               chunk_appendf(buf, " rex=%s",
+                             sc_ep_rcv_ex(scb) ? human_time(TICKS_TO_MS(sc_ep_rcv_ex(scb) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
+               chunk_appendf(buf, " wex=%s",
+                             sc_ep_snd_ex(scb) ? human_time(TICKS_TO_MS(sc_ep_snd_ex(scb) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
+               chunk_appendf(buf, " rto=%s",
+                             tick_isset(sdb->lra) ? human_time(TICKS_TO_MS(tick_add(sdb->lra, scb->ioto) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
+               chunk_appendf(buf, " wto=%s",
+                             tick_isset(sdb->fsb) ? human_time(TICKS_TO_MS(tick_add(sdb->fsb, scb->ioto) - now_ms), TICKS_TO_MS(1000)) : "<NEVER>");
+       }
+
+       chunk_appendf(buf, "\n");
+
+       if (sdb) {
+               chunk_appendf(&trash, "%s    iobuf.flags=0x%08x .pipe=%d .buf=%u@%p+%u/%u\n", pfx,
+                             sdb->iobuf.flags,
+                             sdb->iobuf.pipe ? sdb->iobuf.pipe->data : 0,
+                             sdb->iobuf.buf ? (unsigned int)b_data(sdb->iobuf.buf): 0,
+                             sdb->iobuf.buf ? b_orig(sdb->iobuf.buf): NULL,
+                             sdb->iobuf.buf ? (unsigned int)b_head_ofs(sdb->iobuf.buf): 0,
+                             sdb->iobuf.buf ? (unsigned int)b_size(sdb->iobuf.buf): 0);
+       }
+
+       if (connb) {
+               if (connb->mux && connb->mux->show_sd) {
                        char muxpfx[100] = "";
 
                        snprintf(muxpfx, sizeof(muxpfx), "%s      ", pfx);
                        chunk_appendf(buf, "%s     ", pfx);
-                       conn->mux->show_sd(buf, scb->sedesc, muxpfx);
+                       connb->mux->show_sd(buf, sdb, muxpfx);
                        chunk_appendf(buf, "\n");
                }
 
                chunk_appendf(buf,
                              "%s      co1=%p ctrl=%s xprt=%s mux=%s target=%s:%p\n", pfx,
-                             conn,
-                             conn_get_ctrl_name(conn),
-                             conn_get_xprt_name(conn),
-                             conn_get_mux_name(conn),
-                             obj_type_name(conn->target),
-                             obj_base_ptr(conn->target));
+                             connb,
+                             conn_get_ctrl_name(connb),
+                             conn_get_xprt_name(connb),
+                             conn_get_mux_name(connb),
+                             obj_type_name(connb->target),
+                             obj_base_ptr(connb->target));
 
                chunk_appendf(buf,
                              "%s      flags=0x%08x fd=%u/%d fd.state=%02x updt=%d fd.tmask=0x%lx\n", pfx,
-                             conn->flags,
+                             connb->flags,
                              strm_tgid,
-                             conn_fd(conn),
-                             conn_fd(conn) >= 0 ? strm_fdtab[conn->handle.fd].state : 0,
-                             conn_fd(conn) >= 0 ? !!(strm_fdtab[conn->handle.fd].update_mask & ti->ltid_bit) : 0,
-                             conn_fd(conn) >= 0 ? strm_fdtab[conn->handle.fd].thread_mask: 0);
+                             conn_fd(connb),
+                             conn_fd(connb) >= 0 ? strm_fdtab[connb->handle.fd].state : 0,
+                             conn_fd(connb) >= 0 ? !!(strm_fdtab[connb->handle.fd].update_mask & ti->ltid_bit) : 0,
+                             conn_fd(connb) >= 0 ? strm_fdtab[connb->handle.fd].thread_mask: 0);
        }
-       else if ((tmpctx = sc_appctx(scb)) != NULL) {
+       else if (sdb && (tmpctx = sc_appctx(scb)) != NULL) {
                chunk_appendf(buf,
                              "%s      app1=%p st0=%d st1=%d applet=%s tid=%d nice=%d calls=%u rate=%u\n", pfx,
                              tmpctx,