From 76e32022c4085952eea119fa69976c8bccf2710c Mon Sep 17 00:00:00 2001 From: Stefano Brivio Date: Tue, 23 Apr 2024 22:10:21 +0200 Subject: [PATCH] netlink: Fix iterations over nexthop objects Somewhat confusingly, RTNH_NEXT(), as defined by , doesn't take an attribute length parameter like RTA_NEXT() does, and I just modelled loops over nexthops after RTA loops, forgetting to decrease the remaining length we pass to RTNH_OK(). In practice, this didn't cause issue in any of the combinations I checked, at least without the next patch. We seem to be the only user of RTNH_OK(): even iproute2 has an open-coded version of it in print_rta_multipath() (ip/iproute.c). Introduce RTNH_NEXT_AND_DEC(), similar to RTA_NEXT(), and use it. Fixes: 6c7623d07bbd ("netlink: Add support to fetch default gateway from multipath routes") Fixes: f4e38b5cd232 ("netlink: Adjust interface index inside copied nexthop objects too") Signed-off-by: Stefano Brivio Reviewed-by: David Gibson --- netlink.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/netlink.c b/netlink.c index b3897e6..cdfe68c 100644 --- a/netlink.c +++ b/netlink.c @@ -36,6 +36,10 @@ #include "ip.h" #include "netlink.h" +/* Same as RTA_NEXT() but for nexthops: RTNH_NEXT() doesn't take 'attrlen' */ +#define RTNH_NEXT_AND_DEC(rtnh, attrlen) \ + ((attrlen) -= RTNH_ALIGN((rtnh)->rtnh_len), RTNH_NEXT(rtnh)) + /* Netlink expects a buffer of at least 8kiB or the system page size, * whichever is larger. 32kiB is recommended for more efficient. * Since the largest page size on any remotely common Linux setup is @@ -349,12 +353,13 @@ unsigned int nl_get_ext_if(int s, sa_family_t af) */ bool nl_route_get_def_multipath(struct rtattr *rta, void *gw) { + size_t nh_len = RTA_PAYLOAD(rta); struct rtnexthop *rtnh; bool found = false; int hops = -1; for (rtnh = (struct rtnexthop *)RTA_DATA(rta); - RTNH_OK(rtnh, RTA_PAYLOAD(rta)); rtnh = RTNH_NEXT(rtnh)) { + RTNH_OK(rtnh, nh_len); rtnh = RTNH_NEXT_AND_DEC(rtnh, nh_len)) { size_t len = rtnh->rtnh_len - sizeof(*rtnh); struct rtattr *rta_inner; @@ -566,11 +571,12 @@ int nl_route_dup(int s_src, unsigned int ifi_src, if (rta->rta_type == RTA_OIF) { *(unsigned int *)RTA_DATA(rta) = ifi_dst; } else if (rta->rta_type == RTA_MULTIPATH) { + size_t nh_len = RTA_PAYLOAD(rta); struct rtnexthop *rtnh; for (rtnh = (struct rtnexthop *)RTA_DATA(rta); - RTNH_OK(rtnh, RTA_PAYLOAD(rta)); - rtnh = RTNH_NEXT(rtnh)) + RTNH_OK(rtnh, nh_len); + rtnh = RTNH_NEXT_AND_DEC(rtnh, nh_len)) rtnh->rtnh_ifindex = ifi_dst; } else if (rta->rta_type == RTA_PREFSRC) { /* Host routes might include a preferred source