Hi,
ke, 2025-05-28 kello 17:07 -0400, Luiz Augusto von Dentz kirjoitti:
> From: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
>
> This uses RCU procedures to protect from concurrent access of
> mgmt_pending list which can cause crashes like:
>
> ==================================================================
> BUG: KASAN: slab-use-after-free in mgmt_remove_adv_monitor_complete+0xe5/0x540 net/bluetooth/mgmt.c:5405
> Read of size 8 at addr ffff888048891a18 by task kworker/u5:8/5333
>
> CPU: 0 UID: 0 PID: 5333 Comm: kworker/u5:8 Not tainted 6.15.0-rc5-syzkaller-00197-gea34704d6ad7 #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> Workqueue: hci0 hci_cmd_sync_work
> Call Trace:
> <TASK>
> dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
> print_address_description mm/kasan/report.c:408 [inline]
> print_report+0xb4/0x290 mm/kasan/report.c:521
> kasan_report+0x118/0x150 mm/kasan/report.c:634
> mgmt_remove_adv_monitor_complete+0xe5/0x540 net/bluetooth/mgmt.c:5405
> hci_cmd_sync_work+0x25e/0x3a0 net/bluetooth/hci_sync.c:334
> process_one_work kernel/workqueue.c:3238 [inline]
> process_scheduled_works+0xadb/0x17a0 kernel/workqueue.c:3319
> worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
> kthread+0x70e/0x8a0 kernel/kthread.c:464
> ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
> </TASK>
>
> Allocated by task 5702:
> kasan_save_stack mm/kasan/common.c:47 [inline]
> kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
> poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
> __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:394
> kasan_kmalloc include/linux/kasan.h:260 [inline]
> __kmalloc_cache_noprof+0x230/0x3d0 mm/slub.c:4358
> kmalloc_noprof include/linux/slab.h:905 [inline]
> kzalloc_noprof include/linux/slab.h:1039 [inline]
> mgmt_pending_new+0x65/0x240 net/bluetooth/mgmt_util.c:252
> mgmt_pending_add+0x34/0x120 net/bluetooth/mgmt_util.c:279
> remove_adv_monitor+0x103/0x1b0 net/bluetooth/mgmt.c:5453
> hci_mgmt_cmd+0x9c6/0xef0 net/bluetooth/hci_sock.c:1712
> hci_sock_sendmsg+0x6ca/0xee0 net/bluetooth/hci_sock.c:1832
> sock_sendmsg_nosec net/socket.c:712 [inline]
> __sock_sendmsg+0x219/0x270 net/socket.c:727
> sock_write_iter+0x258/0x330 net/socket.c:1131
> new_sync_write fs/read_write.c:591 [inline]
> vfs_write+0x548/0xa90 fs/read_write.c:684
> ksys_write+0x145/0x250 fs/read_write.c:736
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Freed by task 5700:
> kasan_save_stack mm/kasan/common.c:47 [inline]
> kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
> kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576
> poison_slab_object mm/kasan/common.c:247 [inline]
> __kasan_slab_free+0x62/0x70 mm/kasan/common.c:264
> kasan_slab_free include/linux/kasan.h:233 [inline]
> slab_free_hook mm/slub.c:2380 [inline]
> slab_free mm/slub.c:4642 [inline]
> kfree+0x193/0x440 mm/slub.c:4841
> mgmt_pending_foreach+0xc9/0x120 net/bluetooth/mgmt_util.c:242
> mgmt_index_removed+0x10d/0x2f0 net/bluetooth/mgmt.c:9362
> hci_sock_bind+0xbe9/0x1000 net/bluetooth/hci_sock.c:1307
> __sys_bind_socket net/socket.c:1810 [inline]
> __sys_bind+0x2c3/0x3e0 net/socket.c:1841
> __do_sys_bind net/socket.c:1846 [inline]
> __se_sys_bind net/socket.c:1844 [inline]
> __x64_sys_bind+0x7a/0x90 net/socket.c:1844
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Fixes: a380b6cff1a2 ("Bluetooth: Add generic mgmt helper API")
> Closes: https://syzkaller.appspot.com/bug?extid=feb0dc579bbe30a13190
> Closes: https://syzkaller.appspot.com/bug?extid=0a7039d5d9986ff4ececi
> Closes: https://syzkaller.appspot.com/bug?extid=cc0cc52e7f43dc9e6df1
> Reported-by: syzbot+feb0dc579bbe30a13190@xxxxxxxxxxxxxxxxxxxxxxxxx
> Tested-by: syzbot+feb0dc579bbe30a13190@xxxxxxxxxxxxxxxxxxxxxxxxx
> Tested-by: syzbot+0a7039d5d9986ff4ecec@xxxxxxxxxxxxxxxxxxxxxxxxx
> Tested-by: syzbot+cc0cc52e7f43dc9e6df1@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Dmitry Antipov <dmantipov@xxxxxxxxx>
> Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
> ---
> net/bluetooth/mgmt_util.c | 25 +++++++++++++++----------
> 1 file changed, 15 insertions(+), 10 deletions(-)
>
> diff --git a/net/bluetooth/mgmt_util.c b/net/bluetooth/mgmt_util.c
> index 3713ff490c65..c2dc8ddf5f78 100644
> --- a/net/bluetooth/mgmt_util.c
> +++ b/net/bluetooth/mgmt_util.c
> @@ -219,13 +219,20 @@ struct mgmt_pending_cmd *mgmt_pending_find(unsigned short channel, u16 opcode,
> {
> struct mgmt_pending_cmd *cmd;
>
> - list_for_each_entry(cmd, &hdev->mgmt_pending, list) {
> + rcu_read_lock();
> +
> + list_for_each_entry_rcu(cmd, &hdev->mgmt_pending, list) {
> if (hci_sock_get_channel(cmd->sk) != channel)
> continue;
> - if (cmd->opcode == opcode)
> +
> + if (cmd->opcode == opcode) {
> + rcu_read_unlock();
> return cmd;
RCU does not guarantee the returned pointer is not already freed when
this returns. AFAIK this is exactly the "BUG!!!" mentioned in
https://docs.kernel.org/RCU/whatisRCU.html#rcu-dereference
Instead of calling rcu_read_lock/unlock here, maybe instead
list_for_each_entry_rcu(cmd, &hdev->mgmt_pending, list,
lockdep_is_held(&hdev->lock))
to force caller to either hold rcu_read_lock() or hdev->lock to protect
the return value for the time it needs it.
> + }
> }
>
> + rcu_read_unlock();
> +
> return NULL;
> }
>
> @@ -233,14 +240,11 @@ void mgmt_pending_foreach(u16 opcode, struct hci_dev *hdev,
> void (*cb)(struct mgmt_pending_cmd *cmd, void *data),
> void *data)
> {
> - struct mgmt_pending_cmd *cmd, *tmp;
> -
> - list_for_each_entry_safe(cmd, tmp, &hdev->mgmt_pending, list) {
> - if (opcode > 0 && cmd->opcode != opcode)
> - continue;
> + struct mgmt_pending_cmd *cmd;
>
> + cmd = mgmt_pending_find(HCI_CHANNEL_CONTROL, opcode, hdev);
> + if (cmd)
> cb(cmd, data);
Hence, this is potential UAF, so caller probably shall hold locks as
above.
With the change in list_for_each_entry_rcu(), you'd then get lockdep
splats if caller doesn't hold right locks.
E.g. the UAF in
struct mgmt_pending_cmd *cmd = data;
if (cmd != pending_find(MGMT_OP_SET_POWERED, hdev))
return -ECANCELED;
hci_dev_lock(hdev);
/* operate on cmd */
hci_dev_unlock(hdev);
should be found directly by the assert.
Note that such pattern of checking if a pointer in the "data" of a
delayed callback corresponds to an "alive" object in principle also has
ABA problem (mgmt_pending_free(cmd) + mgmt_pending_add() allocating at
same address -> operates on wrong item). Also hci_conn_valid() has this
issue.
> - }
> }
>
> struct mgmt_pending_cmd *mgmt_pending_new(struct sock *sk, u16 opcode,
> @@ -280,7 +284,7 @@ struct mgmt_pending_cmd *mgmt_pending_add(struct sock *sk, u16 opcode,
> if (!cmd)
> return NULL;
>
> - list_add_tail(&cmd->list, &hdev->mgmt_pending);
> + list_add_tail_rcu(&cmd->list, &hdev->mgmt_pending);
>
> return cmd;
> }
> @@ -294,7 +298,8 @@ void mgmt_pending_free(struct mgmt_pending_cmd *cmd)
>
> void mgmt_pending_remove(struct mgmt_pending_cmd *cmd)
> {
> - list_del(&cmd->list);
> + list_del_rcu(&cmd->list);
> + synchronize_rcu();
Maybe it would be useful to add lockdep_assert_held(&hdev->lock) here
and in mgmt_pending_add() to make sure callers hold right lock?
These compile to nothing with !CONFIG_LOCKDEP so IIUC could be used
more.
> mgmt_pending_free(cmd);
> }
>
--
Pauli Virtanen
