netdev - [PATCH net] bonding: fix use-after-free due to enslave fail after slave array update

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Message-ID: <20260123120659.571187-1-razor@blackwall.org>
Date: Fri, 23 Jan 2026 14:06:59 +0200
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: netdev@...r.kernel.org
Cc: Jay Vosburgh <jv@...sburgh.net>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	davem@...emloft.net,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Nikolay Aleksandrov <razor@...ckwall.org>,
	Chen Zhen <chenzhen126@...wei.com>,
	Jussi Maki <joamaki@...il.com>,
	Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH net] bonding: fix use-after-free due to enslave fail after slave array update

Fix a use-after-free which happens due to enslave failure after the new
slave has been added to the array. Since the new slave can be used for Tx
immediately, we can use it after it has been freed by the enslave error
cleanup path which frees the allocated slave memory. Slave update array is
supposed to be called last when further enslave failures are not expected.
Move it after xdp setup to avoid any problems.

It is very easy to reproduce the problem with a simple xdp_pass prog:
 ip l add bond1 type bond mode balance-xor
 ip l set bond1 up
 ip l set dev bond1 xdp object xdp_pass.o sec xdp_pass
 ip l add dumdum type dummy

Then run in parallel:
 while :; do ip l set dumdum master bond1 1>/dev/null 2>&1; done;
 mausezahn bond1 -a own -b rand -A rand -B 1.1.1.1 -c 0 -t tcp "dp=1-1023, flags=syn"

The crash happens almost immediately:
 [  605.602850] Oops: general protection fault, probably for non-canonical address 0xe0e6fc2460000137: 0000 [#1] SMP KASAN NOPTI
 [  605.602916] KASAN: maybe wild-memory-access in range [0x07380123000009b8-0x07380123000009bf]
 [  605.602946] CPU: 0 UID: 0 PID: 2445 Comm: mausezahn Kdump: loaded Tainted: G    B               6.19.0-rc6+ #21 PREEMPT(voluntary)
 [  605.602979] Tainted: [B]=BAD_PAGE
 [  605.602998] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
 [  605.603032] RIP: 0010:netdev_core_pick_tx+0xcd/0x210
 [  605.603063] Code: 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 3e 01 00 00 48 b8 00 00 00 00 00 fc ff df 4c 8b 6b 08 49 8d 7d 30 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 25 01 00 00 49 8b 45 30 4c 89 e2 48 89 ee 48 89
 [  605.603111] RSP: 0018:ffff88817b9af348 EFLAGS: 00010213
 [  605.603145] RAX: dffffc0000000000 RBX: ffff88817d28b420 RCX: 0000000000000000
 [  605.603172] RDX: 00e7002460000137 RSI: 0000000000000008 RDI: 07380123000009be
 [  605.603199] RBP: ffff88817b541a00 R08: 0000000000000001 R09: fffffbfff3ed8c0c
 [  605.603226] R10: ffffffff9f6c6067 R11: 0000000000000001 R12: 0000000000000000
 [  605.603253] R13: 073801230000098e R14: ffff88817d28b448 R15: ffff88817b541a84
 [  605.603286] FS:  00007f6570ef67c0(0000) GS:ffff888221dfa000(0000) knlGS:0000000000000000
 [  605.603319] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 [  605.603343] CR2: 00007f65712fae40 CR3: 000000011371b000 CR4: 0000000000350ef0
 [  605.603373] Call Trace:
 [  605.603392]  <TASK>
 [  605.603410]  __dev_queue_xmit+0x448/0x32a0
 [  605.603434]  ? __pfx_vprintk_emit+0x10/0x10
 [  605.603461]  ? __pfx_vprintk_emit+0x10/0x10
 [  605.603484]  ? __pfx___dev_queue_xmit+0x10/0x10
 [  605.603507]  ? bond_start_xmit+0xbfb/0xc20 [bonding]
 [  605.603546]  ? _printk+0xcb/0x100
 [  605.603566]  ? __pfx__printk+0x10/0x10
 [  605.603589]  ? bond_start_xmit+0xbfb/0xc20 [bonding]
 [  605.603627]  ? add_taint+0x5e/0x70
 [  605.603648]  ? add_taint+0x2a/0x70
 [  605.603670]  ? end_report.cold+0x51/0x75
 [  605.603693]  ? bond_start_xmit+0xbfb/0xc20 [bonding]
 [  605.603731]  bond_start_xmit+0x623/0xc20 [bonding]

Fixes: 9e2ee5c7e7c3 ("net, bonding: Add XDP support to the bonding driver")
Signed-off-by: Nikolay Aleksandrov <razor@...ckwall.org>
Reported-by: Chen Zhen <chenzhen126@...wei.com>
Closes: https://lore.kernel.org/netdev/fae17c21-4940-5605-85b2-1d5e17342358@huawei.com/
CC: Jussi Maki <joamaki@...il.com>
CC: Daniel Borkmann <daniel@...earbox.net>
---
 drivers/net/bonding/bond_main.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index e7caf400a59c..9a9edf52b651 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2202,11 +2202,6 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev,
 		unblock_netpoll_tx();
 	}
 
-	/* broadcast mode uses the all_slaves to loop through slaves. */
-	if (bond_mode_can_use_xmit_hash(bond) ||
-	    BOND_MODE(bond) == BOND_MODE_BROADCAST)
-		bond_update_slave_arr(bond, NULL);
-
 	if (!slave_dev->netdev_ops->ndo_bpf ||
 	    !slave_dev->netdev_ops->ndo_xdp_xmit) {
 		if (bond->xdp_prog) {
@@ -2240,6 +2235,11 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev,
 			bpf_prog_inc(bond->xdp_prog);
 	}
 
+	/* broadcast mode uses the all_slaves to loop through slaves. */
+	if (bond_mode_can_use_xmit_hash(bond) ||
+	    BOND_MODE(bond) == BOND_MODE_BROADCAST)
+		bond_update_slave_arr(bond, NULL);
+
 	bond_xdp_set_features(bond_dev);
 
 	slave_info(bond_dev, slave_dev, "Enslaving as %s interface with %s link\n",
-- 
2.47.3