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netlink: Fix iterations over nexthop objects

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Somewhat confusingly, RTNH_NEXT(), as defined by <linux/rtnetlink.h>,
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: 6c7623d07b ("netlink: Add support to fetch default gateway from multipath routes")
Fixes: f4e38b5cd2 ("netlink: Adjust interface index inside copied nexthop objects too")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Stefano Brivio 2024-04-23 22:10:21 +02:00
parent d03c4e2020
commit 76e32022c4
1 changed files with 9 additions and 3 deletions
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12
netlink.c
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@ -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