bpf/bonding: reject vlan+srcmac xmit_hash_policy change when XDP is loaded

bond_option_mode_set() already rejects mode changes that would make a
loaded XDP program incompatible via bond_xdp_check().  However,
bond_option_xmit_hash_policy_set() has no such guard.

For 802.3ad and balance-xor modes, bond_xdp_check() returns false when
xmit_hash_policy is vlan+srcmac, because the 802.1q payload is usually
absent due to hardware offload.  This means a user can:

1. Attach a native XDP program to a bond in 802.3ad/balance-xor mode
   with a compatible xmit_hash_policy (e.g. layer2+3).
2. Change xmit_hash_policy to vlan+srcmac while XDP remains loaded.

This leaves bond->xdp_prog set but bond_xdp_check() now returning false
for the same device.  When the bond is later destroyed, dev_xdp_uninstall()
calls bond_xdp_set(dev, NULL, NULL) to remove the program, which hits
the bond_xdp_check() guard and returns -EOPNOTSUPP, triggering:

WARN_ON(dev_xdp_install(dev, mode, bpf_op, NULL, 0, NULL))

Fix this by rejecting xmit_hash_policy changes to vlan+srcmac when an
XDP program is loaded on a bond in 802.3ad or balance-xor mode.

commit 39a0876d595b ("net, bonding: Disallow vlan+srcmac with XDP")
introduced bond_xdp_check() which returns false for 802.3ad/balance-xor
modes when xmit_hash_policy is vlan+srcmac.  The check was wired into
bond_xdp_set() to reject XDP attachment with an incompatible policy, but
the symmetric path -- preventing xmit_hash_policy from being changed to an
incompatible value after XDP is already loaded -- was left unguarded in
bond_option_xmit_hash_policy_set().

Note:
commit 094ee6017ea0 ("bonding: check xdp prog when set bond mode")
later added a similar guard to bond_option_mode_set(), but
bond_option_xmit_hash_policy_set() remained unprotected.

Reported-by: syzbot+5a287bcdc08104bc3132@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/6995aff6.050a0220.2eeac1.014e.GAE@google.com/T/
Fixes: 39a0876d595b ("net, bonding: Disallow vlan+srcmac with XDP")
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
Link: https://patch.msgid.link/20260226080306.98766-2-jiayuan.chen@linux.dev
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

3 files changed, 10 insertions, 2 deletions

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index a1de08ee3815..14ed91391fcc 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -324,7 +324,7 @@ static bool bond_sk_check(struct bonding *bond)
 	}
 }
 
-bool bond_xdp_check(struct bonding *bond, int mode)
+bool __bond_xdp_check(int mode, int xmit_policy)
 {
 	switch (mode) {
 	case BOND_MODE_ROUNDROBIN:
@@ -335,7 +335,7 @@ bool bond_xdp_check(struct bonding *bond, int mode)
 		/* vlan+srcmac is not supported with XDP as in most cases the 802.1q
 		 * payload is not in the packet due to hardware offload.
 		 */
-		if (bond->params.xmit_policy != BOND_XMIT_POLICY_VLAN_SRCMAC)
+		if (xmit_policy != BOND_XMIT_POLICY_VLAN_SRCMAC)
 			return true;
 		fallthrough;
 	default:
@@ -343,6 +343,11 @@ bool bond_xdp_check(struct bonding *bond, int mode)
 	}
 }
 
+bool bond_xdp_check(struct bonding *bond, int mode)
+{
+	return __bond_xdp_check(mode, bond->params.xmit_policy);
+}
+
 /*---------------------------------- VLAN -----------------------------------*/
 
 /* In the following 2 functions, bond_vlan_rx_add_vid and bond_vlan_rx_kill_vid,
diff --git a/drivers/net/bonding/bond_options.c b/drivers/net/bonding/bond_options.c
index dcee384c2f06..7380cc4ee75a 100644
--- a/drivers/net/bonding/bond_options.c
+++ b/drivers/net/bonding/bond_options.c
@@ -1575,6 +1575,8 @@ static int bond_option_fail_over_mac_set(struct bonding *bond,
 static int bond_option_xmit_hash_policy_set(struct bonding *bond,
 					    const struct bond_opt_value *newval)
 {
+	if (bond->xdp_prog && !__bond_xdp_check(BOND_MODE(bond), newval->value))
+		return -EOPNOTSUPP;
 	netdev_dbg(bond->dev, "Setting xmit hash policy to %s (%llu)\n",
 		   newval->string, newval->value);
 	bond->params.xmit_policy = newval->value;
diff --git a/include/net/bonding.h b/include/net/bonding.h
index 4ad5521e7731..395c6e281c5f 100644
--- a/include/net/bonding.h
+++ b/include/net/bonding.h
@@ -699,6 +699,7 @@ void bond_debug_register(struct bonding *bond);
 void bond_debug_unregister(struct bonding *bond);
 void bond_debug_reregister(struct bonding *bond);
 const char *bond_mode_name(int mode);
+bool __bond_xdp_check(int mode, int xmit_policy);
 bool bond_xdp_check(struct bonding *bond, int mode);
 void bond_setup(struct net_device *bond_dev);
 unsigned int bond_get_num_tx_queues(void);