Re: [PATCH] Bluetooth: L2CAP: Fix use-after-free

From: Sungwoo Kim
Date: Thu Feb 02 2023 - 07:09:30 EST

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In reply to: Eric Dumazet: "Re: [PATCH] Bluetooth: L2CAP: Fix use-after-free"
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On Thu, Feb 2, 2023 at 4:26 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> On Thu, Feb 2, 2023 at 10:07 AM Sungwoo Kim <iam@xxxxxxxxxxxx> wrote:
> >
> > Due to the race condition between l2cap_sock_cleanup_listen and
> > l2cap_sock_close_cb, l2cap_sock_kill can receive already freed sk,
> > resulting in use-after-free inside l2cap_sock_kill.
> > This patch prevent this by adding a null check in l2cap_sock_kill.
> >
> > Context 1:
> > l2cap_sock_cleanup_listen();
> > // context switched
> > l2cap_chan_lock(chan);
> > l2cap_sock_kill(sk); // <-- sk is already freed below
>
> But sk is used in l2cap_sock_cleanup_listen()
> and should not be NULL...
>
> while ((sk = bt_accept_dequeue(parent, NULL))) {
> ...
> l2cap_sock_kill(sk);
> ..
> }
>
> It would help if you send us a stack trace ...

Here is the stack trace and l2cap_sock.c:
https://gist.github.com/swkim101/5c3b8cb7c7d7172aef23810c9412f323

==================================================================
BUG: KASAN: use-after-free in l2cap_sock_kill (/v6.1-rc2/./include/net/sock.h:986 /v6.1-rc2/net/bluetooth/l2cap_sock.c:1281)
Read of size 8 at addr ffff88800f7f4060 by task l2cap-server/1764
CPU: 0 PID: 1764 Comm: l2cap-server Not tainted 6.1.0-rc2 #129
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl (/v6.1-rc2/lib/dump_stack.c:105)
print_address_description+0x7e/0x360
print_report (/v6.1-rc2/mm/kasan/report.c:187 /v6.1-rc2/mm/kasan/report.c:389)
? __virt_addr_valid (/v6.1-rc2/./include/linux/mmzone.h:1855 /v6.1-rc2/arch/x86/mm/physaddr.c:65)
? kasan_complete_mode_report_info (/v6.1-rc2/mm/kasan/report_generic.c:104 /v6.1-rc2/mm/kasan/report_generic.c:127 /v6.1-rc2/mm/kasan/report_generic.c:136)
? l2cap_sock_kill (/v6.1-rc2/./include/net/sock.h:986 /v6.1-rc2/net/bluetooth/l2cap_sock.c:1281)
kasan_report (/v6.1-rc2/mm/kasan/report.c:? /v6.1-rc2/mm/kasan/report.c:484)
? l2cap_sock_kill (/v6.1-rc2/./include/net/sock.h:986 /v6.1-rc2/net/bluetooth/l2cap_sock.c:1281)
kasan_check_range (/v6.1-rc2/mm/kasan/generic.c:85 /v6.1-rc2/mm/kasan/generic.c:115 /v6.1-rc2/mm/kasan/generic.c:128 /v6.1-rc2/mm/kasan/generic.c:159 /v6.1-rc2/mm/kasan/generic.c:180 /v6.1-rc2/mm/kasan/generic.c:189)
__kasan_check_read (/v6.1-rc2/mm/kasan/shadow.c:31)
l2cap_sock_kill (/v6.1-rc2/./include/net/sock.h:986 /v6.1-rc2/net/bluetooth/l2cap_sock.c:1281)
l2cap_sock_teardown_cb (/v6.1-rc2/./include/net/bluetooth/bluetooth.h:304 /v6.1-rc2/net/bluetooth/l2cap_sock.c:1475 /v6.1-rc2/net/bluetooth/l2cap_sock.c:1612)
l2cap_chan_close (/v6.1-rc2/net/bluetooth/l2cap_core.c:885)
? __kasan_check_write (/v6.1-rc2/mm/kasan/shadow.c:37)
l2cap_sock_shutdown (/v6.1-rc2/./include/linux/kcsan-checks.h:231 /v6.1-rc2/./include/net/sock.h:2470 /v6.1-rc2/net/bluetooth/l2cap_sock.c:1321 /v6.1-rc2/net/bluetooth/l2cap_sock.c:1377)
? _raw_write_unlock (/v6.1-rc2/./include/asm-generic/qrwlock.h:122 /v6.1-rc2/./include/linux/rwlock_api_smp.h:225 /v6.1-rc2/kernel/locking/spinlock.c:342)
l2cap_sock_release (/v6.1-rc2/net/bluetooth/l2cap_sock.c:1453)
sock_close (/v6.1-rc2/net/socket.c:1382)
? sock_mmap (/v6.1-rc2/net/socket.c:?)
__fput (/v6.1-rc2/./include/linux/fsnotify.h:? /v6.1-rc2/./include/linux/fsnotify.h:99 /v6.1-rc2/./include/linux/fsnotify.h:341 /v6.1-rc2/fs/file_table.c:306)
____fput (/v6.1-rc2/fs/file_table.c:348)
task_work_run (/v6.1-rc2/kernel/task_work.c:165)
do_exit (/v6.1-rc2/kernel/exit.c:?)
do_group_exit (/v6.1-rc2/kernel/exit.c:943)
? __kasan_check_write (/v6.1-rc2/mm/kasan/shadow.c:37)
get_signal (/v6.1-rc2/kernel/signal.c:2863)
? _raw_spin_unlock (/v6.1-rc2/./include/linux/spinlock_api_smp.h:142 /v6.1-rc2/kernel/locking/spinlock.c:186)
? finish_task_switch (/v6.1-rc2/./arch/x86/include/asm/current.h:15 /v6.1-rc2/kernel/sched/core.c:5065)
arch_do_signal_or_restart (/v6.1-rc2/arch/x86/kernel/signal.c:869)
exit_to_user_mode_prepare (/v6.1-rc2/kernel/entry/common.c:383)
syscall_exit_to_user_mode (/v6.1-rc2/./arch/x86/include/asm/current.h:15 /v6.1-rc2/kernel/entry/common.c:261 /v6.1-rc2/kernel/entry/common.c:283 /v6.1-rc2/kernel/entry/common.c:296)
do_syscall_64 (/v6.1-rc2/arch/x86/entry/common.c:50 /v6.1-rc2/arch/x86/entry/common.c:80)
? sysvec_apic_timer_interrupt (/v6.1-rc2/arch/x86/kernel/apic/apic.c:1107)
entry_SYSCALL_64_after_hwframe (/v6.1-rc2/arch/x86/entry/entry_64.S:120)
RIP: 0033:0x7f66c14db970
Code: Unable to access opcode bytes at 0x7f66c14db946.

Code starting with the faulting instruction
===========================================
RSP: 002b:00007ffe166a5508 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: 0000000000000013 RBX: 0000000000000013 RCX: 00007f66c14db970
RDX: 0000000000000013 RSI: 00007ffe166a56d0 RDI: 0000000000000002
RBP: 00007ffe166a56d0 R08: 00007f66c1a28440 R09: 0000000000000013
R10: 0000000000000078 R11: 0000000000000246 R12: 0000000000000013
R13: 0000000000000001 R14: 00007f66c179a520 R15: 0000000000000013
</TASK>
Allocated by task 77:
kasan_set_track (/v6.1-rc2/mm/kasan/common.c:51)
kasan_save_alloc_info (/v6.1-rc2/mm/kasan/generic.c:432 /v6.1-rc2/mm/kasan/generic.c:498)
__kasan_kmalloc (/v6.1-rc2/mm/kasan/common.c:356)
__kmalloc (/v6.1-rc2/mm/slab_common.c:943 /v6.1-rc2/mm/slab_common.c:968)
sk_prot_alloc (/v6.1-rc2/net/core/sock.c:2028)
sk_alloc (/v6.1-rc2/net/core/sock.c:2083)
l2cap_sock_alloc (/v6.1-rc2/net/bluetooth/l2cap_sock.c:1903)
l2cap_sock_new_connection_cb (/v6.1-rc2/net/bluetooth/l2cap_sock.c:1504)
l2cap_connect (/v6.1-rc2/net/bluetooth/l2cap_core.c:102 /v6.1-rc2/net/bluetooth/l2cap_core.c:4277)
l2cap_bredr_sig_cmd (/v6.1-rc2/net/bluetooth/l2cap_core.c:5634 /v6.1-rc2/net/bluetooth/l2cap_core.c:5927)
l2cap_recv_frame (/v6.1-rc2/net/bluetooth/l2cap_core.c:7851 /v6.1-rc2/net/bluetooth/l2cap_core.c:7919)
l2cap_recv_acldata (/v6.1-rc2/net/bluetooth/l2cap_core.c:8601 /v6.1-rc2/net/bluetooth/l2cap_core.c:8631)
hci_rx_work (/v6.1-rc2/./include/net/bluetooth/hci_core.h:1121 /v6.1-rc2/net/bluetooth/hci_core.c:3937 /v6.1-rc2/net/bluetooth/hci_core.c:4189)
process_one_work (/v6.1-rc2/kernel/workqueue.c:2225)
worker_thread (/v6.1-rc2/kernel/workqueue.c:816 /v6.1-rc2/kernel/workqueue.c:2107 /v6.1-rc2/kernel/workqueue.c:2159 /v6.1-rc2/kernel/workqueue.c:2408)
kthread (/v6.1-rc2/kernel/kthread.c:361)
ret_from_fork (/v6.1-rc2/arch/x86/entry/entry_64.S:306)
Freed by task 52:
kasan_set_track (/v6.1-rc2/mm/kasan/common.c:51)
kasan_save_free_info (/v6.1-rc2/mm/kasan/generic.c:508)
____kasan_slab_free (/v6.1-rc2/./include/linux/slub_def.h:164 /v6.1-rc2/mm/kasan/common.c:214)
__kasan_slab_free (/v6.1-rc2/mm/kasan/common.c:244)
slab_free_freelist_hook (/v6.1-rc2/mm/slub.c:381 /v6.1-rc2/mm/slub.c:1747)
__kmem_cache_free (/v6.1-rc2/mm/slub.c:3656 /v6.1-rc2/mm/slub.c:3674)
kfree (/v6.1-rc2/mm/slab_common.c:1007)
__sk_destruct (/v6.1-rc2/./include/linux/cred.h:288 /v6.1-rc2/net/core/sock.c:2147)
__sk_free (/v6.1-rc2/./include/linux/sock_diag.h:87 /v6.1-rc2/net/core/sock.c:2175)
sk_free (/v6.1-rc2/./include/linux/instrumented.h:? /v6.1-rc2/./include/linux/atomic/atomic-instrumented.h:176 /v6.1-rc2/./include/linux/refcount.h:272 /v6.1-rc2/./include/linux/refcount.h:315 /v6.1-rc2/./include/linux/refcount.h:333 /v6.1-rc2/net/core/sock.c:2188)
l2cap_sock_kill (/v6.1-rc2/./include/net/bluetooth/bluetooth.h:286 /v6.1-rc2/net/bluetooth/l2cap_sock.c:1284)
l2cap_sock_close_cb (/v6.1-rc2/net/bluetooth/l2cap_sock.c:1576)
l2cap_chan_timeout (/v6.1-rc2/./include/net/bluetooth/bluetooth.h:296 /v6.1-rc2/net/bluetooth/l2cap_core.c:462)
process_one_work (/v6.1-rc2/kernel/workqueue.c:2225)
worker_thread (/v6.1-rc2/kernel/workqueue.c:816 /v6.1-rc2/kernel/workqueue.c:2107 /v6.1-rc2/kernel/workqueue.c:2159 /v6.1-rc2/kernel/workqueue.c:2408)
kthread (/v6.1-rc2/kernel/kthread.c:361)
ret_from_fork (/v6.1-rc2/arch/x86/entry/entry_64.S:306)
The buggy address belongs to the object at ffff88800f7f4000
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 96 bytes inside of
1024-byte region [ffff88800f7f4000, ffff88800f7f4400)
The buggy address belongs to the physical page:
page:00000000b8d65c1d refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88800f7f6800 pfn:0xf7f4
head:00000000b8d65c1d order:2 compound_mapcount:0 compound_pincount:0
flags: 0xfffffc0010200(slab|head|node=0|zone=1|lastcpupid=0x1fffff)
raw: 000fffffc0010200 ffffea0000993408 ffffea0000991308 ffff888005841dc0
raw: ffff88800f7f6800 0000000000080002 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff88800f7f3f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88800f7f3f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88800f7f4000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88800f7f4080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88800f7f4100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

> >
> > Context 2:
> > l2cap_chan_timeout();
> > l2cap_chan_lock(chan);
> > chan->ops->close(chan);
> > l2cap_sock_close_cb()
> > l2cap_sock_kill(sk); // <-- sk is freed here
> > l2cap_chan_unlock(chan);
> >
>
> Please add a Fixes: tag

Fixes: 6c08fc896b60 ("Bluetooth: Fix refcount use-after-free issue")
> > Signed-off-by: Sungwoo Kim <iam@xxxxxxxxxxxx>
> > ---
> > net/bluetooth/l2cap_sock.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
> > index ca8f07f35..657704059 100644
> > --- a/net/bluetooth/l2cap_sock.c
> > +++ b/net/bluetooth/l2cap_sock.c
> > @@ -1245,7 +1245,7 @@ static int l2cap_sock_recvmsg(struct socket *sock, struct msghdr *msg,
> > */
> > static void l2cap_sock_kill(struct sock *sk)
> > {
> > - if (!sock_flag(sk, SOCK_ZAPPED) || sk->sk_socket)
> > + if (!sk || !sock_flag(sk, SOCK_ZAPPED) || sk->sk_socket)
> > return;
> >
> > BT_DBG("sk %p state %s", sk, state_to_string(sk->sk_state));
> > --
> > 2.25.1
> >

Next message: patchwork-bot+netdevbpf: "Re: [PATCH net-next 00/13] rxrpc: Increasing SACK size and moving away from softirq, part 5"
Previous message: Greg KH: "Re: [PATCH] bcache: Fix a NULL or wild pointer dereference in btree_split"
In reply to: Eric Dumazet: "Re: [PATCH] Bluetooth: L2CAP: Fix use-after-free"
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