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[sched] Detect cycles and bound zombie host chain traversal #7418

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[sched] Detect cycles and bound zombie host chain traversal #7418

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37 changes: 35 additions & 2 deletions sched/handle_request.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -63,6 +63,11 @@ using std::string;
#include "sched_util.h"
#include "time_stats_log.h"

// max number of zombie host links to follow in authenticate_user().
// Guards against cycles and excessively long chains.
//
#define MAX_ZOMBIE_HOST_LINKS 16

// are the 2 hosts obviously different computers?
//
static bool obviously_different(HOST& h1, HOST& h2) {
Expand Down Expand Up @@ -295,12 +300,39 @@ int authenticate_user() {
DB_TEAM team;

if (g_request->hostid) {
DB_ID_TYPE visited[MAX_ZOMBIE_HOST_LINKS];
int nlinks = 0;
retval = host.lookup_id(g_request->hostid);
while (!retval && host.userid==0) {
// if host record is zombie, follow link to new host
// TODO: check for infinite loop
//
retval = host.lookup_id(host.rpc_seqno);
if (host.rpc_seqno <= 0) {
log_messages.printf(MSG_CRITICAL,
"[HOST#%lu] invalid target %d in zombie host chain (at host %lu)\n",
g_request->hostid, host.rpc_seqno, host.id
);
retval = ERR_DB_NOT_FOUND;
break;
}
DB_ID_TYPE next_id = host.rpc_seqno;
bool cycle = (next_id == host.id);
for (int i = 0; i < nlinks && !cycle; i++) {
if (visited[i] == next_id) {
cycle = true;
}
}
if (cycle || nlinks >= MAX_ZOMBIE_HOST_LINKS) {
log_messages.printf(MSG_CRITICAL,
"[HOST#%lu] %s zombie host chain (at host %lu -> %lu)\n",
g_request->hostid,
cycle ? "cycle in" : "too many links in",
host.id, next_id
);
retval = ERR_DB_NOT_FOUND;
break;
}
visited[nlinks++] = host.id;
retval = host.lookup_id(next_id);
if (!retval) {
g_reply->hostid = host.id;
log_messages.printf(MSG_NORMAL,
Expand All @@ -319,6 +351,7 @@ int authenticate_user() {
g_request->hostid
);
g_request->hostid = 0;
g_reply->hostid = 0;
goto lookup_user_and_make_new_host;
}

Expand Down
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