net/ipv6/ndisc.c:1362 ndisc_router_discovery() warn: unsigned 'rtime' is never less than zero.

From: kernel test robot
Date: Sat Aug 22 2020 - 16:32:41 EST

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tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head: c3d8f220d01220a5b253e422be407d068dc65511
commit: 19e16d220f0adbf899a652dfb1fde2e3a95153e9 neigh: support smaller retrans_time settting
date: 5 months ago
config: mips-randconfig-m031-20200823 (attached as .config)
compiler: mipsel-linux-gcc (GCC) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@xxxxxxxxx>

smatch warnings:
net/ipv6/ndisc.c:1362 ndisc_router_discovery() warn: unsigned 'rtime' is never less than zero.

# https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=19e16d220f0adbf899a652dfb1fde2e3a95153e9
git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
git fetch --no-tags linus master
git checkout 19e16d220f0adbf899a652dfb1fde2e3a95153e9
vim +/rtime +1362 net/ipv6/ndisc.c

1238
1239 if (in6_dev->if_flags & IF_RS_SENT) {
1240 /*
1241 * flag that an RA was received after an RS was sent
1242 * out on this interface.
1243 */
1244 in6_dev->if_flags |= IF_RA_RCVD;
1245 }
1246
1247 /*
1248 * Remember the managed/otherconf flags from most recently
1249 * received RA message (RFC 2462) -- yoshfuji
1250 */
1251 old_if_flags = in6_dev->if_flags;
1252 in6_dev->if_flags = (in6_dev->if_flags & ~(IF_RA_MANAGED |
1253 IF_RA_OTHERCONF)) |
1254 (ra_msg->icmph.icmp6_addrconf_managed ?
1255 IF_RA_MANAGED : 0) |
1256 (ra_msg->icmph.icmp6_addrconf_other ?
1257 IF_RA_OTHERCONF : 0);
1258
1259 if (old_if_flags != in6_dev->if_flags)
1260 send_ifinfo_notify = true;
1261
1262 if (!in6_dev->cnf.accept_ra_defrtr) {
1263 ND_PRINTK(2, info,
1264 "RA: %s, defrtr is false for dev: %s\n",
1265 __func__, skb->dev->name);
1266 goto skip_defrtr;
1267 }
1268
1269 /* Do not accept RA with source-addr found on local machine unless
1270 * accept_ra_from_local is set to true.
1271 */
1272 net = dev_net(in6_dev->dev);
1273 if (!in6_dev->cnf.accept_ra_from_local &&
1274 ipv6_chk_addr(net, &ipv6_hdr(skb)->saddr, in6_dev->dev, 0)) {
1275 ND_PRINTK(2, info,
1276 "RA from local address detected on dev: %s: default router ignored\n",
1277 skb->dev->name);
1278 goto skip_defrtr;
1279 }
1280
1281 lifetime = ntohs(ra_msg->icmph.icmp6_rt_lifetime);
1282
1283 #ifdef CONFIG_IPV6_ROUTER_PREF
1284 pref = ra_msg->icmph.icmp6_router_pref;
1285 /* 10b is handled as if it were 00b (medium) */
1286 if (pref == ICMPV6_ROUTER_PREF_INVALID ||
1287 !in6_dev->cnf.accept_ra_rtr_pref)
1288 pref = ICMPV6_ROUTER_PREF_MEDIUM;
1289 #endif
1290 /* routes added from RAs do not use nexthop objects */
1291 rt = rt6_get_dflt_router(net, &ipv6_hdr(skb)->saddr, skb->dev);
1292 if (rt) {
1293 neigh = ip6_neigh_lookup(&rt->fib6_nh->fib_nh_gw6,
1294 rt->fib6_nh->fib_nh_dev, NULL,
1295 &ipv6_hdr(skb)->saddr);
1296 if (!neigh) {
1297 ND_PRINTK(0, err,
1298 "RA: %s got default router without neighbour\n",
1299 __func__);
1300 fib6_info_release(rt);
1301 return;
1302 }
1303 }
1304 if (rt && lifetime == 0) {
1305 ip6_del_rt(net, rt);
1306 rt = NULL;
1307 }
1308
1309 ND_PRINTK(3, info, "RA: rt: %p lifetime: %d, for dev: %s\n",
1310 rt, lifetime, skb->dev->name);
1311 if (!rt && lifetime) {
1312 ND_PRINTK(3, info, "RA: adding default router\n");
1313
1314 rt = rt6_add_dflt_router(net, &ipv6_hdr(skb)->saddr,
1315 skb->dev, pref);
1316 if (!rt) {
1317 ND_PRINTK(0, err,
1318 "RA: %s failed to add default route\n",
1319 __func__);
1320 return;
1321 }
1322
1323 neigh = ip6_neigh_lookup(&rt->fib6_nh->fib_nh_gw6,
1324 rt->fib6_nh->fib_nh_dev, NULL,
1325 &ipv6_hdr(skb)->saddr);
1326 if (!neigh) {
1327 ND_PRINTK(0, err,
1328 "RA: %s got default router without neighbour\n",
1329 __func__);
1330 fib6_info_release(rt);
1331 return;
1332 }
1333 neigh->flags |= NTF_ROUTER;
1334 } else if (rt) {
1335 rt->fib6_flags = (rt->fib6_flags & ~RTF_PREF_MASK) | RTF_PREF(pref);
1336 }
1337
1338 if (rt)
1339 fib6_set_expires(rt, jiffies + (HZ * lifetime));
1340 if (in6_dev->cnf.accept_ra_min_hop_limit < 256 &&
1341 ra_msg->icmph.icmp6_hop_limit) {
1342 if (in6_dev->cnf.accept_ra_min_hop_limit <= ra_msg->icmph.icmp6_hop_limit) {
1343 in6_dev->cnf.hop_limit = ra_msg->icmph.icmp6_hop_limit;
1344 fib6_metric_set(rt, RTAX_HOPLIMIT,
1345 ra_msg->icmph.icmp6_hop_limit);
1346 } else {
1347 ND_PRINTK(2, warn, "RA: Got route advertisement with lower hop_limit than minimum\n");
1348 }
1349 }
1350
1351 skip_defrtr:
1352
1353 /*
1354 * Update Reachable Time and Retrans Timer
1355 */
1356
1357 if (in6_dev->nd_parms) {
1358 unsigned long rtime = ntohl(ra_msg->retrans_timer);
1359
1360 if (rtime && rtime/1000 < MAX_SCHEDULE_TIMEOUT/HZ) {
1361 rtime = (rtime*HZ)/1000;
> 1362 if (rtime < HZ/100)
1363 rtime = HZ/100;
1364 NEIGH_VAR_SET(in6_dev->nd_parms, RETRANS_TIME, rtime);
1365 in6_dev->tstamp = jiffies;
1366 send_ifinfo_notify = true;
1367 }
1368
1369 rtime = ntohl(ra_msg->reachable_time);
1370 if (rtime && rtime/1000 < MAX_SCHEDULE_TIMEOUT/(3*HZ)) {
1371 rtime = (rtime*HZ)/1000;
1372
1373 if (rtime < HZ/10)
1374 rtime = HZ/10;
1375
1376 if (rtime != NEIGH_VAR(in6_dev->nd_parms, BASE_REACHABLE_TIME)) {
1377 NEIGH_VAR_SET(in6_dev->nd_parms,
1378 BASE_REACHABLE_TIME, rtime);
1379 NEIGH_VAR_SET(in6_dev->nd_parms,
1380 GC_STALETIME, 3 * rtime);
1381 in6_dev->nd_parms->reachable_time = neigh_rand_reach_time(rtime);
1382 in6_dev->tstamp = jiffies;
1383 send_ifinfo_notify = true;
1384 }
1385 }
1386 }
1387
1388 /*
1389 * Send a notify if RA changed managed/otherconf flags or timer settings
1390 */
1391 if (send_ifinfo_notify)
1392 inet6_ifinfo_notify(RTM_NEWLINK, in6_dev);
1393
1394 skip_linkparms:
1395
1396 /*
1397 * Process options.
1398 */
1399
1400 if (!neigh)
1401 neigh = __neigh_lookup(&nd_tbl, &ipv6_hdr(skb)->saddr,
1402 skb->dev, 1);
1403 if (neigh) {
1404 u8 *lladdr = NULL;
1405 if (ndopts.nd_opts_src_lladdr) {
1406 lladdr = ndisc_opt_addr_data(ndopts.nd_opts_src_lladdr,
1407 skb->dev);
1408 if (!lladdr) {
1409 ND_PRINTK(2, warn,
1410 "RA: invalid link-layer address length\n");
1411 goto out;
1412 }
1413 }
1414 ndisc_update(skb->dev, neigh, lladdr, NUD_STALE,
1415 NEIGH_UPDATE_F_WEAK_OVERRIDE|
1416 NEIGH_UPDATE_F_OVERRIDE|
1417 NEIGH_UPDATE_F_OVERRIDE_ISROUTER|
1418 NEIGH_UPDATE_F_ISROUTER,
1419 NDISC_ROUTER_ADVERTISEMENT, &ndopts);
1420 }
1421
1422 if (!ipv6_accept_ra(in6_dev)) {
1423 ND_PRINTK(2, info,
1424 "RA: %s, accept_ra is false for dev: %s\n",
1425 __func__, skb->dev->name);
1426 goto out;
1427 }
1428

---
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https://lists.01.org/hyperkitty/list/kbuild-all@xxxxxxxxxxxx

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Next message: Joe Perches: "Re: [PATCH net-next] net: Remove unnecessary intermediate variables"
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