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Message-ID: <20250723195443.448163-1-kuniyu@google.com>
Date: Wed, 23 Jul 2025 19:53:59 +0000
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Gilad Naaman <gnaaman@...venets.com>,
Kuniyuki Iwashima <kuniyu@...gle.com>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org,
kernel test robot <oliver.sang@...el.com>
Subject: [PATCH v1 net] neighbour: Fix null-ptr-deref in neigh_flush_dev().
kernel test robot reported null-ptr-deref in neigh_flush_dev(). [0]
The cited commit introduced per-netdev neighbour list and converted
neigh_flush_dev() to use it instead of the global hash table.
One thing we missed is that neigh_table_clear() calls neigh_ifdown()
with NULL dev.
Let's restore the hash table iteration.
Note that IPv6 module is no longer unloadable, so neigh_table_clear()
is called only when IPv6 fails to initialise, which is unlikely to
happen.
[0]:
IPv6: Attempt to unregister permanent protocol 136
IPv6: Attempt to unregister permanent protocol 17
Oops: general protection fault, probably for non-canonical address 0xdffffc00000001a0: 0000 [#1] SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000d00-0x0000000000000d07]
CPU: 1 UID: 0 PID: 1 Comm: systemd Tainted: G T 6.12.0-rc6-01246-gf7f52738637f #1
Tainted: [T]=RANDSTRUCT
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:neigh_flush_dev.llvm.6395807810224103582+0x52/0x570
Code: c1 e8 03 42 8a 04 38 84 c0 0f 85 15 05 00 00 31 c0 41 83 3e 0a 0f 94 c0 48 8d 1c c3 48 81 c3 f8 0c 00 00 48 89 d8 48 c1 e8 03 <42> 80 3c 38 00 74 08 48 89 df e8 f7 49 93 fe 4c 8b 3b 4d 85 ff 0f
RSP: 0000:ffff88810026f408 EFLAGS: 00010206
RAX: 00000000000001a0 RBX: 0000000000000d00 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffc0631640
RBP: ffff88810026f470 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffffffffc0625250 R14: ffffffffc0631640 R15: dffffc0000000000
FS: 00007f575cb83940(0000) GS:ffff8883aee00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f575db40008 CR3: 00000002bf936000 CR4: 00000000000406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__neigh_ifdown.llvm.6395807810224103582+0x44/0x390
neigh_table_clear+0xb1/0x268
ndisc_cleanup+0x21/0x38 [ipv6]
init_module+0x2f5/0x468 [ipv6]
do_one_initcall+0x1ba/0x628
do_init_module+0x21a/0x530
load_module+0x2550/0x2ea0
__se_sys_finit_module+0x3d2/0x620
__x64_sys_finit_module+0x76/0x88
x64_sys_call+0x7ff/0xde8
do_syscall_64+0xfb/0x1e8
entry_SYSCALL_64_after_hwframe+0x67/0x6f
RIP: 0033:0x7f575d6f2719
Code: 08 89 e8 5b 5d c3 66 2e 0f 1f 84 00 00 00 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d b7 06 0d 00 f7 d8 64 89 01 48
RSP: 002b:00007fff82a2a268 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
RAX: ffffffffffffffda RBX: 0000557827b45310 RCX: 00007f575d6f2719
RDX: 0000000000000000 RSI: 00007f575d584efd RDI: 0000000000000004
RBP: 00007f575d584efd R08: 0000000000000000 R09: 0000557827b47b00
R10: 0000000000000004 R11: 0000000000000246 R12: 0000000000020000
R13: 0000000000000000 R14: 0000557827b470e0 R15: 00007f575dbb4270
</TASK>
Modules linked in: ipv6(+)
Fixes: f7f52738637f4 ("neighbour: Create netdev->neighbour association")
Reported-by: kernel test robot <oliver.sang@...el.com>
Closes: https://lore.kernel.org/oe-lkp/202507200931.7a89ecd8-lkp@intel.com
Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
---
net/core/neighbour.c | 88 ++++++++++++++++++++++++++++++--------------
1 file changed, 61 insertions(+), 27 deletions(-)
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 49dce9a82295b..a8dc72eda2027 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -368,6 +368,43 @@ static void pneigh_queue_purge(struct sk_buff_head *list, struct net *net,
}
}
+static void neigh_flush_one(struct neighbour *n)
+{
+ hlist_del_rcu(&n->hash);
+ hlist_del_rcu(&n->dev_list);
+
+ write_lock(&n->lock);
+
+ neigh_del_timer(n);
+ neigh_mark_dead(n);
+
+ if (refcount_read(&n->refcnt) != 1) {
+ /* The most unpleasant situation.
+ * We must destroy neighbour entry,
+ * but someone still uses it.
+ *
+ * The destroy will be delayed until
+ * the last user releases us, but
+ * we must kill timers etc. and move
+ * it to safe state.
+ */
+ __skb_queue_purge(&n->arp_queue);
+ n->arp_queue_len_bytes = 0;
+ WRITE_ONCE(n->output, neigh_blackhole);
+
+ if (n->nud_state & NUD_VALID)
+ n->nud_state = NUD_NOARP;
+ else
+ n->nud_state = NUD_NONE;
+
+ neigh_dbg(2, "neigh %p is stray\n", n);
+ }
+
+ write_unlock(&n->lock);
+
+ neigh_cleanup_and_release(n);
+}
+
static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev,
bool skip_perm)
{
@@ -381,32 +418,24 @@ static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev,
if (skip_perm && n->nud_state & NUD_PERMANENT)
continue;
- hlist_del_rcu(&n->hash);
- hlist_del_rcu(&n->dev_list);
- write_lock(&n->lock);
- neigh_del_timer(n);
- neigh_mark_dead(n);
- if (refcount_read(&n->refcnt) != 1) {
- /* The most unpleasant situation.
- * We must destroy neighbour entry,
- * but someone still uses it.
- *
- * The destroy will be delayed until
- * the last user releases us, but
- * we must kill timers etc. and move
- * it to safe state.
- */
- __skb_queue_purge(&n->arp_queue);
- n->arp_queue_len_bytes = 0;
- WRITE_ONCE(n->output, neigh_blackhole);
- if (n->nud_state & NUD_VALID)
- n->nud_state = NUD_NOARP;
- else
- n->nud_state = NUD_NONE;
- neigh_dbg(2, "neigh %p is stray\n", n);
- }
- write_unlock(&n->lock);
- neigh_cleanup_and_release(n);
+ neigh_flush_one(n);
+ }
+}
+
+static void neigh_flush_table(struct neigh_table *tbl)
+{
+ struct neigh_hash_table *nht;
+ int i;
+
+ nht = rcu_dereference_protected(tbl->nht,
+ lockdep_is_held(&tbl->lock));
+
+ for (i = 0; i < (1 << nht->hash_shift); i++) {
+ struct hlist_node *tmp;
+ struct neighbour *n;
+
+ neigh_for_each_in_bucket_safe(n, tmp, &nht->hash_heads[i])
+ neigh_flush_one(n);
}
}
@@ -422,7 +451,12 @@ static int __neigh_ifdown(struct neigh_table *tbl, struct net_device *dev,
bool skip_perm)
{
write_lock_bh(&tbl->lock);
- neigh_flush_dev(tbl, dev, skip_perm);
+ if (likely(dev)) {
+ neigh_flush_dev(tbl, dev, skip_perm);
+ } else {
+ DEBUG_NET_WARN_ON_ONCE(skip_perm);
+ neigh_flush_table(tbl);
+ }
pneigh_ifdown_and_unlock(tbl, dev);
pneigh_queue_purge(&tbl->proxy_queue, dev ? dev_net(dev) : NULL,
tbl->family);
--
2.50.1.470.g6ba607880d-goog
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