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Tue, 06 Oct 2026 00:35:29 -0700 (PDT) From: Cen Zhang To: marcel@holtmann.org, luiz.dentz@gmail.com Cc: linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, jjzuming@gmail.com, zzzccc427@gmail.com Subject: [PATCH] Bluetooth: 6LoWPAN: Use RCU-safe device list removal Date: Tue, 6 Oct 2026 15:35:23 +0800 Message-Id: X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit RCU readers of bt_6lowpan_devices must be able to follow an adapter's forward link until their read-side critical section ends. The entries are published with list_add_rcu(), but device_event() removes an entry on NETDEV_UNREGISTER with list_del(), poisoning that link. When an adapter is being unregistered and 6LoWPAN is enabled, a 6lowpan_control debugfs write with an existing LE L2CAP connection can enter lookup_peer() after unregister's first synchronize_net(). If the connection has no peer on that adapter, the reader must advance to the next list entry. Neither RTNL nor devices_lock excludes this RCU reader. The last peer's chan_close_cb() schedules delete_netdev(), which reaches unregister_netdevice_many_notify() through unregister_dev() and lowpan_unregister_netdev(). The following ordering is possible: Unregister worker Control writer ----------------- -------------- synchronize_net() returns lowpan_control_write() lookup_peer(): rcu_read_lock() reach adapter; no matching peer device_event(): devices_lock list_del(&entry->list) spin_unlock(&devices_lock) follow poisoned next link read invalid adapter address post-notifier synchronize_net() waits for the reader This invalid pointer access can fault in lookup_peer(). The first grace period drains existing readers but permits new ones to start, and the later grace period cannot prevent the intervening poisoned-link access. Use list_del_rcu() under the existing devices_lock to preserve the forward link for readers that already reached the adapter. The existing post-notifier synchronize_net() waits for those readers before netdevice teardown frees the private storage containing lowpan_btle_dev. KASAN report as below: [...] [ 45.867526] Oops: general protection fault, probably for non-canonical address 0xfbd59c0000000023: 0000 [#1] SMP KASAN NOPTI [ 45.869489] KASAN: maybe wild-memory-access in range [0xdead000000000118-0xdead00000000011f] [ 45.870981] CPU: 1 UID: 0 PID: 646 Comm: sh Not tainted 7.2.0-rc6-pmb-bt-functional-v1+ #4 PREEMPT(lazy) [ 45.872609] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [ 45.874380] RIP: 0010:lookup_peer+0x1ba/0x320 [ 45.875067] Code: 48 89 d9 ba 04 00 00 00 4c 89 fe bf a0 06 00 00 e8 2b e8 ad fb e9 56 ff ff ff e8 01 1e c3 fb 49 8d 7f 18 48 89 f8 48 c1 e8 03 <80> 3c 28 00 0f 85 4a 01 00 00 4d 8b 47 18 4c 89 f1 ba 04 00 00 00 [ 45.878206] RSP: 0018:ffff888114d67b90 EFLAGS: 00010212 [ 45.879106] RAX: 1bd5a00000000023 RBX: 0000000000000000 RCX: ffffffff85c1d19f [ 45.880334] RDX: ffff88810dc35700 RSI: 0000000000000000 RDI: dead000000000118 [ 45.881455] RBP: dffffc0000000000 R08: 0000000000000001 R09: 0000000000000001 [ 45.882546] R10: ffffffff893d3057 R11: ffff88810dc35700 R12: ffff88810a690000 [ 45.883839] R13: ffff888115451038 R14: ffff88810a690000 R15: dead000000000100 [ 45.885186] FS: 00007fa889bac780(0000) GS:ffff8881fd852000(0000) knlGS:0000000000000000 [ 45.886539] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 45.887527] CR2: 00007ffe304f2f80 CR3: 0000000104f64005 CR4: 0000000000770ef0 [ 45.888687] PKRU: 55555554 [ 45.889183] Call Trace: [ 45.889666] [ 45.890061] lowpan_control_write+0x445/0x9e0 [ 45.890854] ? __pfx_lowpan_control_write+0x10/0x10 [ 45.891738] ? srso_alias_return_thunk+0x5/0xfbef5 [ 45.892603] ? srso_alias_return_thunk+0x5/0xfbef5 [ 45.893383] ? __debugfs_file_get+0x1bd/0x7f0 [ 45.894057] ? srso_alias_return_thunk+0x5/0xfbef5 [ 45.894902] ? lock_acquire+0x17b/0x2f0 [ 45.895593] ? ksys_write+0x111/0x200 [ 45.896290] full_proxy_write+0x11f/0x180 [ 45.896991] vfs_write+0x25a/0x1010 [ 45.897642] ? __pfx_full_proxy_write+0x10/0x10 [ 45.898440] ? __pfx_vfs_write+0x10/0x10 [ 45.899178] ? lock_release+0x11f/0x280 [ 45.899855] ksys_write+0x111/0x200 [ 45.900435] ? __pfx_ksys_write+0x10/0x10 [ 45.901074] ? irqentry_exit+0xbe/0x820 [ 45.901722] ? srso_alias_return_thunk+0x5/0xfbef5 [ 45.902489] do_syscall_64+0x115/0x6a0 [ 45.903064] entry_SYSCALL_64_after_hwframe+0x77/0x7f [ 45.903813] RIP: 0033:0x7fa889c3e687 [ 45.904359] Code: 48 89 fa 4c 89 df e8 58 b3 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff [ 45.906981] RSP: 002b:00007ffd7651b960 EFLAGS: 00000202 ORIG_RAX: 0000000000000001 [ 45.908070] RAX: ffffffffffffffda RBX: 00007fa889bac780 RCX: 00007fa889c3e687 [ 45.909102] RDX: 000000000000001c RSI: 00005570f25e8d10 RDI: 0000000000000001 [ 45.910133] RBP: 00005570f25e8d10 R08: 0000000000000000 R09: 0000000000000000 [ 45.911162] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000001 [ 45.912190] R13: 000000000000001c R14: 0000000000000000 R15: 00005570f25e8a78 [ 45.913208] [ 45.913530] Modules linked in: [ 45.914022] ---[ end trace 0000000000000000 ]--- [ 45.914709] RIP: 0010:lookup_peer+0x1ba/0x320 [ 45.915436] Code: 48 89 d9 ba 04 00 00 00 4c 89 fe bf a0 06 00 00 e8 2b e8 ad fb e9 56 ff ff ff e8 01 1e c3 fb 49 8d 7f 18 48 89 f8 48 c1 e8 03 <80> 3c 28 00 0f 85 4a 01 00 00 4d 8b 47 18 4c 89 f1 ba 04 00 00 00 [ 45.919191] RSP: 0018:ffff888114d67b90 EFLAGS: 00010212 [ 45.920046] RAX: 1bd5a00000000023 RBX: 0000000000000000 RCX: ffffffff85c1d19f [ 45.921129] RDX: ffff88810dc35700 RSI: 0000000000000000 RDI: dead000000000118 [ 45.922553] RBP: dffffc0000000000 R08: 0000000000000001 R09: 0000000000000001 [ 45.923653] R10: ffffffff893d3057 R11: ffff88810dc35700 R12: ffff88810a690000 [ 45.925119] R13: ffff888115451038 R14: ffff88810a690000 R15: dead000000000100 [ 45.926180] FS: 00007fa889bac780(0000) GS:ffff8881fd852000(0000) knlGS:0000000000000000 [ 45.927817] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 45.928726] CR2: 00007ffe304f2f80 CR3: 0000000104f64005 CR4: 0000000000770ef0 [ 45.930069] PKRU: 55555554 [ 45.930456] Kernel panic - not syncing: Fatal exception [ 45.931542] Kernel Offset: disabled [ 45.932040] Rebooting in 1 seconds.. Fixes: 90305829635d ("Bluetooth: 6lowpan: Converting rwlocks to use RCU") Assisted-by: LLM Signed-off-by: Cen Zhang --- diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c index 836add41f5..4b05409929 100644 --- a/net/bluetooth/6lowpan.c +++ b/net/bluetooth/6lowpan.c @@ -1274,7 +1274,7 @@ static int device_event(struct notifier_block *unused, if (entry->netdev == netdev) { BT_DBG("Unregistered netdev %s %p", netdev->name, netdev); - list_del(&entry->list); + list_del_rcu(&entry->list); break; } }