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ipv4: stop route notification sizing when nexthop group shrinks

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Commit 680aea08e7 ("net: ipv4: Emit notification when fib
hardware flags are changed") added an RCU-only fib_nlmsg_size() call
for asynchronous hardware flag notifications.

fib_nlmsg_size() checks fib_info_num_path() before each iteration,
then fib_info_nhc() independently reloads nh->nh_grp. If
RTM_NEWNEXTHOP replaces a group with fewer paths between those loads,
fib_info_nhc() returns NULL and fib_nexthop_nlmsg_size() dereferences
it.

Stop sizing when the indexed path is absent. Nexthop groups are
dense, so the current snapshot has no later path.

Fixes: 680aea08e7 ("net: ipv4: Emit notification when fib hardware flags are changed")
Cc: stable@vger.kernel.org
Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/1054fa46165bba1b473782fa41367804aa908e86.1790915964.git.4ncienth@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Daehyeon Ko 2026-10-02 13:51:00 +09:00 committed by Jakub Kicinski
parent 4f4afc07dc
commit d3daa33c7a
1 changed files with 3 additions and 0 deletions
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3
net/ipv4/fib_semantics.c
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@ -542,6 +542,9 @@ size_t fib_nlmsg_size(struct fib_info *fi)
struct fib_nh_common *nhc = fib_info_nhc(fi, i);
size_t nhsize;
if (!nhc)
break;
nhsize = fib_nexthop_nlmsg_size(nhc, nhs != 1);
if (nhs != 1)