Subject: Re: [PATCH v4 0/2] net: bonding: fix type-confusion in bonding header_ops

From: "Jiayuan Chen" <[email-masked]>
Date: Fri, 06 Mar 2026 08:13:45 +0000

March 6, 2026 at 04:59, "Jay Vosburgh" <[email-masked] mailto:[email-masked]?to=%22Jay%20Vosburgh%22%20%3Cjv%40jvosburgh.net%3E > wrote:

> 
> Kota Toda <[email-masked]> wrote:
> 
> > 
> > In bond_setup_by_slave(), the slave’s header_ops are unconditionally
> > copied into the bonding device. As a result, the bonding device may invoke
> > the slave-specific header operations on itself, causing
> > netdev_priv(bond_dev) (a struct bonding) to be incorrectly interpreted
> > as the slave's private-data type.
> > 
> > This type-confusion bug can lead to out-of-bounds writes into the skb,
> > resulting in memory corruption.
> > 
>  A few days ago, Jiayuan Chen <[email-masked]> posted a
> fix for what sounds like the same problem[0]. Their solution appears to
> be much less complicated.
> 
>  I also wonder how this bug was discovered. The code in question
> hasn't changed in many years, and now there are two independent fixes
> within a week.

This issue has existed for years, but was likely masked by other bugs in the IP GRE
module.
https://syzkaller.appspot.com/bug?extid=4c63f36709a642f801c5
https://syzkaller.appspot.com/bug?id=77135d6c2fc52eff1b3c561912fbec39761e0461

The recent commit e67c577d8989 ("ipv4: ip_gre: make ipgre_header() robust"), which
introduced pskb_expand_head, has made the wrong type-casting issue more apparent.

v2 was sent:
https://lore.kernel.org/netdev/[email-masked]/

> [0] https://lore.kernel.org/netdev/[email-masked]/
> 
> > 
> > Patch 1 stores the slave's header_ops in struct bonding and sets
> > wrapper callbacks in bond_In bond_setup_by_slave(), the slave’s
> > header_ops are unconditionally
> > copied into the bonding device. As a result, the bonding device may invoke
> > the slave-specific header operations on itself, causing
> > netdev_priv(bond_dev) (a struct bonding) to be incorrectly interpreted
> > as the slave's private-data type.
> > 
> > Patch 2 uses READ_ONCE when loading header_ops callbacks
> > to avoid races with concurrent updates.
> > 
>  With the READ_ONCE changes in a separate patch, does that mean
> that patch 1 by itself is subject to race conditions that would result
> in errors? If so, that's not acceptable, every patch must stand alone
> and not break the kernel.
> 
>  -J
> 
> > 
> > Fixes: 1284cd3a2b74 ("bonding: two small fixes for IPoIB support")
> > Signed-off-by: Kota Toda <[email-masked]>
> > Co-developed-by: Yuki Koike <[email-masked]>
> > Signed-off-by: Yuki Koike <[email-masked]>
> > 
> > Kota Toda (2):
> >  net: bonding: fix type-confusion in bonding header_ops
> >  net: add READ_ONCE for header_ops callbacks
> > 
> >  drivers/net/bonding/bond_main.c | 67 ++++++++++++++++++++++++++++++++-
> >  include/linux/netdevice.h | 41 ++++++++++++++------
> >  include/net/bonding.h | 5 +++
> >  include/net/cfg802154.h | 2 +-
> >  net/core/neighbour.c | 6 +--
> >  net/ipv4/arp.c | 2 +-
> >  net/ipv6/ndisc.c | 2 +-
> >  7 files changed, 106 insertions(+), 19 deletions(-)
> > 
> > -- 
> > 2.53.0
> > 
> ---
>  -Jay Vosburgh, [email-masked]
>