On 06/05/2020 22:46, Cong Wang 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>
> ---
The patch looks good, but note that __netdev_update_features() used to return -1
before the commit in the Fixes tag above (between 6cb6a27c45ce and
00ee59271777).
It only restored that behaviour.
> 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);
> }
> }
> }
>
