Re: Re: [PATCH v3] Bluetooth: call lock_sock() outside of spinlock section

[LinMa <linma@zju.edu.cn>]

Hi there,

I'm just exhilarated to see there have been some new ideas to fix this.

> 
> How about we revert back to use bh_lock_sock_nested but use
> local_bh_disable like the following patch:
> 
> https://patchwork.kernel.org/project/bluetooth/patch/20210713162838.693266-1-desmondcheongzx@gmail.com/
> 

I have checked that patch and learn about some `local_bh_disable/enable` usage.
To the best of my knowledge, the local_bh_disable() function can be used to disable the processing of bottom halves (softirqs).
Or in another word, if process context function, hci_sock_sendmsg() for example, can mask the BH (hci_dev_do_close()?). It doesn't need to worry about the UAF.

However, after doing some experiments, I failed :(
For instance, I try to do following patch:

--- a/net/bluetooth/hci_sock.c
+++ b/net/bluetooth/hci_sock.c
@@ -1720,6 +1720,7 @@ static int hci_sock_sendmsg(struct socket *sock, struct msghdr *msg,
                return -EINVAL;

        lock_sock(sk);
+       local_bh_disable();

        switch (hci_pi(sk)->channel) {
        case HCI_CHANNEL_RAW:
@@ -1832,7 +1833,9 @@ static int hci_sock_sendmsg(struct socket *sock, struct msghdr *msg,
        err = len;

 done:
+       local_bh_enable();
        release_sock(sk);
+
        return err;

But the POC code shows error message like below:

[   18.169155] BUG: sleeping function called from invalid context at include/linux/sched/mm.h:197
[   18.170181] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 120, name: exp
[   18.170987] 1 lock held by exp/120:
[   18.171384]  #0: ffff888011dd5120 (sk_lock-AF_BLUETOOTH-BTPROTO_HCI){+.+.}-{0:0}, at: hci_sock_sendmsg+0x11e/0x26c0
[   18.172300] CPU: 0 PID: 120 Comm: exp Not tainted 5.11.11+ #44
[   18.172921] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
...

The patch provided by Desmond adds the local_bh_disable() before the bh_lock_sock() so I also try that in 

--- a/net/bluetooth/hci_sock.c
+++ b/net/bluetooth/hci_sock.c
@@ -762,6 +762,7 @@ void hci_sock_dev_event(struct hci_dev *hdev, int event)
                /* Detach sockets from device */
                read_lock(&hci_sk_list.lock);
                sk_for_each(sk, &hci_sk_list.head) {
+                       local_bh_disable();
                        bh_lock_sock_nested(sk);
                        if (hci_pi(sk)->hdev == hdev) {
                                hci_pi(sk)->hdev = NULL;
@@ -772,6 +773,7 @@ void hci_sock_dev_event(struct hci_dev *hdev, int event)
                                hci_dev_put(hdev);
                        }
                        bh_unlock_sock(sk);
+                       local_bh_enable();
                }
                read_unlock(&hci_sk_list.lock);
        }

But this is not useful, the UAF still occurs

[   13.862117] ==================================================================
[   13.863064] BUG: KASAN: use-after-free in __lock_acquire+0xe5/0x2ca0
[   13.863852] Read of size 8 at addr ffff888011d9aeb0 by task exp/119
[   13.864620]
[   13.864818] CPU: 0 PID: 119 Comm: exp Not tainted 5.11.11+ #45
[   13.865543] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
[   13.866634] Call Trace:
[   13.866947]  dump_stack+0x183/0x22e
[   13.867389]  ? show_regs_print_info+0x12/0x12
[   13.867927]  ? log_buf_vmcoreinfo_setup+0x45d/0x45d
[   13.868503]  ? _raw_spin_lock_irqsave+0xbd/0x100
[   13.869244]  print_address_description+0x7b/0x3a0
[   13.869828]  __kasan_report+0x14e/0x200
[   13.870288]  ? __lock_acquire+0xe5/0x2ca0
[   13.870768]  kasan_report+0x47/0x60
[   13.871189]  __lock_acquire+0xe5/0x2ca0
[   13.871647]  ? lock_acquire+0x168/0x6a0
[   13.872107]  ? trace_lock_release+0x5c/0x120
[   13.872615]  ? do_user_addr_fault+0x9c2/0xdb0
[   13.873135]  ? trace_lock_acquire+0x150/0x150
[   13.873661]  ? rcu_read_lock_sched_held+0x87/0x110
[   13.874232]  ? perf_trace_rcu_barrier+0x360/0x360
[   13.874790]  ? avc_has_perm_noaudit+0x442/0x4c0
[   13.875332]  lock_acquire+0x168/0x6a0
[   13.875772]  ? skb_queue_tail+0x32/0x120
[   13.876240]  ? do_kern_addr_fault+0x230/0x230
[   13.876756]  ? read_lock_is_recursive+0x10/0x10
[   13.877300]  ? exc_page_fault+0xf3/0x1b0
[   13.877770]  ? cred_has_capability+0x191/0x3f0
[   13.878290]  ? cred_has_capability+0x2a1/0x3f0
[   13.878816]  ? rcu_lock_release+0x20/0x20
[   13.879295]  _raw_spin_lock_irqsave+0xb1/0x100
[   13.879821]  ? skb_queue_tail+0x32/0x120
[   13.880287]  ? _raw_spin_lock+0x40/0x40
[   13.880745]  skb_queue_tail+0x32/0x120
[   13.881194]  hci_sock_sendmsg+0x1545/0x26b0

From my point of view, adding the local_bh_disable() cannot prevent current hci_sock_dev_event() to set and decrease the ref-count. It's not quite similar with the cases that Desmond discussed.
(Or maybe just I don't know how to use this).

I recently tried to find some similar cases (and I did, reported to security already but get no reply) and figure out how others are fixed.
Some guideline tells me that (http://books.gigatux.nl/mirror/kerneldevelopment/0672327201/ch07lev1sec6.html)

"If process context code and a bottom half share data, you need to disable bottom-half processing and obtain a lock before accessing the data. Doing both ensures local and SMP protection and prevents a deadlock."

Assuming hci_sock_sendmsg()/hci_sock_bound_ioctl() are the process contexts while the hci_sock_dev_event(), not sure, is the BH context. The fact is that the hci_sock_dev_event() should wait for the process contexts. Hence, I think Tetsuo is on the right way.

Regards
Lock-Noob LinMa