Cong Wang <xiyou.wangc...@gmail.com> wrote:
>syzbot managed to trigger a recursive NETDEV_FEAT_CHANGE event
>between bonding master and slave. I managed to find a reproducer
>for this:
>
> ip li set bond0 up
> ifenslave bond0 eth0
> brctl addbr br0
> ethtool -K eth0 lro off
> brctl addif br0 bond0
> ip li set br0 up
>
>When a NETDEV_FEAT_CHANGE event is triggered on a bonding slave,
>it captures this and calls bond_compute_features() to fixup its
>master's and other slaves' features. However, when syncing with
>its lower devices by netdev_sync_lower_features() this event is
>triggered again on slaves when the LRO feature fails to change,
>so it goes back and forth recursively until the kernel stack is
>exhausted.
>
>Commit 17b85d29e82c intentionally lets __netdev_update_features()
>return -1 for such a failure case, so we have to just rely on
>the existing check inside netdev_sync_lower_features() and skip
>NETDEV_FEAT_CHANGE event only for this specific failure case.
>
>Fixes: 17b85d29e82c ("net/core: revert "net: fix __netdev_update_features
>return.." and add comment")
>Reported-by: syzbot+e73ceacfd8560cc8a...@syzkaller.appspotmail.com
>Reported-by: syzbot+c2fb6f9ddcea95ba4...@syzkaller.appspotmail.com
>Cc: Nikolay Aleksandrov <niko...@cumulusnetworks.com>
>Cc: Josh Poimboeuf <jpoim...@redhat.com>
>Cc: Jay Vosburgh <j.vosbu...@gmail.com>
>Cc: Jann Horn <ja...@google.com>
>Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
Reviewed-by: Jay Vosburgh <jay.vosbu...@canonical.com>
>---
> net/core/dev.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
>diff --git a/net/core/dev.c b/net/core/dev.c
>index 522288177bbd..6d327b7aa813 100644
>--- a/net/core/dev.c
>+++ b/net/core/dev.c
>@@ -8907,11 +8907,13 @@ static void netdev_sync_lower_features(struct
>net_device *upper,
> netdev_dbg(upper, "Disabling feature %pNF on lower dev
> %s.\n",
> &feature, lower->name);
> lower->wanted_features &= ~feature;
>- netdev_update_features(lower);
>+ __netdev_update_features(lower);
>
> if (unlikely(lower->features & feature))
> netdev_WARN(upper, "failed to disable %pNF on
> %s!\n",
> &feature, lower->name);
>+ else
>+ netdev_features_change(lower);
> }
> }
> }
>--
>2.26.2
>
