net: bonding: fix NULL deref in bond_debug_rlb_hash_show

rlb_clear_slave intentionally keeps RLB hash-table entries on
the rx_hashtbl_used_head list with slave set to NULL when no
replacement slave is available. However, bond_debug_rlb_hash_show
visites client_info->slave without checking if it's NULL.

Other used-list iterators in bond_alb.c already handle this NULL-slave
state safely:

- rlb_update_client returns early on !client_info->slave
- rlb_req_update_slave_clients, rlb_clear_slave, and rlb_rebalance
compare slave values before visiting
- lb_req_update_subnet_clients continues if slave is NULL

The following NULL deref crash can be trigger in
bond_debug_rlb_hash_show:

[    1.289791] BUG: kernel NULL pointer dereference, address: 0000000000000000
[    1.292058] RIP: 0010:bond_debug_rlb_hash_show (drivers/net/bonding/bond_debugfs.c:41)
[    1.293101] RSP: 0018:ffffc900004a7d00 EFLAGS: 00010286
[    1.293333] RAX: 0000000000000000 RBX: ffff888102b48200 RCX: ffff888102b48204
[    1.293631] RDX: ffff888102b48200 RSI: ffffffff839daad5 RDI: ffff888102815078
[    1.293924] RBP: ffff888102815078 R08: ffff888102b4820e R09: 0000000000000000
[    1.294267] R10: 0000000000000000 R11: 0000000000000000 R12: ffff888100f929c0
[    1.294564] R13: ffff888100f92a00 R14: 0000000000000001 R15: ffffc900004a7ed8
[    1.294864] FS:  0000000001395380(0000) GS:ffff888196e75000(0000) knlGS:0000000000000000
[    1.295239] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    1.295480] CR2: 0000000000000000 CR3: 0000000102adc004 CR4: 0000000000772ef0
[    1.295897] Call Trace:
[    1.296134]  seq_read_iter (fs/seq_file.c:231)
[    1.296341]  seq_read (fs/seq_file.c:164)
[    1.296493]  full_proxy_read (fs/debugfs/file.c:378 (discriminator 1))
[    1.296658]  vfs_read (fs/read_write.c:572)
[    1.296981]  ksys_read (fs/read_write.c:717)
[    1.297132]  do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1))
[    1.297325]  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)

Add a NULL check and print "(none)" for entries with no assigned slave.

Fixes: caafa84251b88 ("bonding: add the debugfs interface to see RLB hash table")
Reported-by: Weiming Shi <bestswngs@gmail.com>
Signed-off-by: Xiang Mei <xmei5@asu.edu>
Link: https://patch.msgid.link/20260317005034.1888794-1-xmei5@asu.edu
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 11 insertions, 5 deletions

diff --git a/drivers/net/bonding/bond_debugfs.c b/drivers/net/bonding/bond_debugfs.c
index 8adbec7c5084..8967b65f6d84 100644
--- a/drivers/net/bonding/bond_debugfs.c
+++ b/drivers/net/bonding/bond_debugfs.c
@@ -34,11 +34,17 @@ static int bond_debug_rlb_hash_show(struct seq_file *m, void *v)
 	for (; hash_index != RLB_NULL_INDEX;
 	     hash_index = client_info->used_next) {
 		client_info = &(bond_info->rx_hashtbl[hash_index]);
-		seq_printf(m, "%-15pI4 %-15pI4 %-17pM %s\n",
-			&client_info->ip_src,
-			&client_info->ip_dst,
-			&client_info->mac_dst,
-			client_info->slave->dev->name);
+		if (client_info->slave)
+			seq_printf(m, "%-15pI4 %-15pI4 %-17pM %s\n",
+				   &client_info->ip_src,
+				   &client_info->ip_dst,
+				   &client_info->mac_dst,
+				   client_info->slave->dev->name);
+		else
+			seq_printf(m, "%-15pI4 %-15pI4 %-17pM (none)\n",
+				   &client_info->ip_src,
+				   &client_info->ip_dst,
+				   &client_info->mac_dst);
 	}
 
 	spin_unlock_bh(&bond->mode_lock);