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Subject: Re: memory leak in h4_recv_buf
From:   Marcel Holtmann <marcel@holtmann.org>
In-Reply-To: <a125c3e6-7723-185a-3c47-219c201c6785@gmail.com>
Date:   Thu, 29 Jul 2021 13:44:13 +0200
Cc:     syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org
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Message-Id: <E59B3DB2-3D96-459B-9902-C9E729407ED2@holtmann.org>
References: <0000000000006b1779058c0cbdda@google.com>
 <d71a274f-fdeb-4da1-898e-06f6944e04dan@googlegroups.com>
 <a125c3e6-7723-185a-3c47-219c201c6785@gmail.com>
To:     Phi Nguyen <phind.uet@gmail.com>
Precedence: bulk

Hi Phi,

>>    Hello,
>>    syzbot found the following crash on:
>>    HEAD commit: abf02e29 Merge tag 'pm-5.2-rc6' of
>>    git://git.kernel.org/pu <http://git.kernel.org/pu>..
>>    git tree: upstream
>>    console output:
>>    https://syzkaller.appspot.com/x/log.txt?x=1054e6b2a00000
>>    <https://syzkaller.appspot.com/x/log.txt?x=1054e6b2a00000>
>>    kernel config:
>>    https://syzkaller.appspot.com/x/.config?x=56f1da14935c3cce
>>    <https://syzkaller.appspot.com/x/.config?x=56f1da14935c3cce>
>>    dashboard link:
>>    https://syzkaller.appspot.com/bug?extid=97388eb9d31b997fe1d0
>>    <https://syzkaller.appspot.com/bug?extid=97388eb9d31b997fe1d0>
>>    compiler: gcc (GCC) 9.0.0 20181231 (experimental)
>>    syz repro:
>>    https://syzkaller.appspot.com/x/repro.syz?x=1073d8aaa00000
>>    <https://syzkaller.appspot.com/x/repro.syz?x=1073d8aaa00000>
>>    C reproducer:
>>    https://syzkaller.appspot.com/x/repro.c?x=17b36fbea00000
>>    <https://syzkaller.appspot.com/x/repro.c?x=17b36fbea00000>
>>    IMPORTANT: if you fix the bug, please add the following tag to the
>>    commit:
>>    Reported-by: syzbot+97388e...@syzkaller.appspotmail.com
>>    program
>>    BUG: memory leak
>>    unreferenced object 0xffff88810991fa00 (size 224):
>>    comm "syz-executor739", pid 7080, jiffies 4294949854 (age 18.640s)
>>    hex dump (first 32 bytes):
>>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>>    backtrace:
>>    [<00000000da42c09f>] kmemleak_alloc_recursive
>>    include/linux/kmemleak.h:43 [inline]
>>    [<00000000da42c09f>] slab_post_alloc_hook mm/slab.h:439 [inline]
>>    [<00000000da42c09f>] slab_alloc_node mm/slab.c:3269 [inline]
>>    [<00000000da42c09f>] kmem_cache_alloc_node+0x153/0x2a0 mm/slab.c:3579
>>    [<00000000f6fbcf84>] __alloc_skb+0x6e/0x210 net/core/skbuff.c:194
>>    [<00000000ea93fc4c>] alloc_skb include/linux/skbuff.h:1054 [inline]
>>    [<00000000ea93fc4c>] bt_skb_alloc include/net/bluetooth/bluetooth.h:339
>>    [inline]
>>    [<00000000ea93fc4c>] h4_recv_buf+0x26d/0x450
>>    drivers/bluetooth/hci_h4.c:182
>>    [<00000000e0312475>] h4_recv+0x51/0xb0 drivers/bluetooth/hci_h4.c:116
>>    [<00000000ebf11fab>] hci_uart_tty_receive+0xba/0x200
>>    drivers/bluetooth/hci_ldisc.c:592
>>    [<0000000095e1216e>] tiocsti drivers/tty/tty_io.c:2195 [inline]
>>    [<0000000095e1216e>] tty_ioctl+0x81c/0xa30 drivers/tty/tty_io.c:2571
>>    [<000000009fa523f0>] vfs_ioctl fs/ioctl.c:46 [inline]
>>    [<000000009fa523f0>] file_ioctl fs/ioctl.c:509 [inline]
>>    [<000000009fa523f0>] do_vfs_ioctl+0x62a/0x810 fs/ioctl.c:696
>>    [<000000000cebb5d9>] ksys_ioctl+0x86/0xb0 fs/ioctl.c:713
>>    [<000000001630008a>] __do_sys_ioctl fs/ioctl.c:720 [inline]
>>    [<000000001630008a>] __se_sys_ioctl fs/ioctl.c:718 [inline]
>>    [<000000001630008a>] __x64_sys_ioctl+0x1e/0x30 fs/ioctl.c:718
>>    [<00000000c62091e3>] do_syscall_64+0x76/0x1a0
>>    arch/x86/entry/common.c:301
>>    [<000000005c213625>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>    BUG: memory leak
>>    unreferenced object 0xffff8881204f4400 (size 1024):
>>    comm "syz-executor739", pid 7080, jiffies 4294949854 (age 18.640s)
>>    hex dump (first 32 bytes):
>>    6c 69 62 75 64 65 76 00 fe ed ca fe 28 00 00 00 libudev.....(...
>>    28 00 00 00 a0 00 00 00 52 ca da 77 00 00 00 00 (.......R..w....
>>    backtrace:
>>    [<0000000034504843>] kmemleak_alloc_recursive
>>    include/linux/kmemleak.h:43 [inline]
>>    [<0000000034504843>] slab_post_alloc_hook mm/slab.h:439 [inline]
>>    [<0000000034504843>] slab_alloc_node mm/slab.c:3269 [inline]
>>    [<0000000034504843>] kmem_cache_alloc_node_trace+0x15b/0x2a0
>>    mm/slab.c:3597
>>    [<0000000056d30eb5>] __do_kmalloc_node mm/slab.c:3619 [inline]
>>    [<0000000056d30eb5>] __kmalloc_node_track_caller+0x38/0x50
>>    mm/slab.c:3634
>>    [<00000000df40176c>] __kmalloc_reserve.isra.0+0x40/0xb0
>>    net/core/skbuff.c:138
>>    [<0000000035340e64>] __alloc_skb+0xa0/0x210 net/core/skbuff.c:206
>>    [<00000000ea93fc4c>] alloc_skb include/linux/skbuff.h:1054 [inline]
>>    [<00000000ea93fc4c>] bt_skb_alloc include/net/bluetooth/bluetooth.h:339
>>    [inline]
>>    [<00000000ea93fc4c>] h4_recv_buf+0x26d/0x450
>>    drivers/bluetooth/hci_h4.c:182
>>    [<00000000e0312475>] h4_recv+0x51/0xb0 drivers/bluetooth/hci_h4.c:116
>>    [<00000000ebf11fab>] hci_uart_tty_receive+0xba/0x200
>>    drivers/bluetooth/hci_ldisc.c:592
>>    [<0000000095e1216e>] tiocsti drivers/tty/tty_io.c:2195 [inline]
>>    [<0000000095e1216e>] tty_ioctl+0x81c/0xa30 drivers/tty/tty_io.c:2571
>>    [<000000009fa523f0>] vfs_ioctl fs/ioctl.c:46 [inline]
>>    [<000000009fa523f0>] file_ioctl fs/ioctl.c:509 [inline]
>>    [<000000009fa523f0>] do_vfs_ioctl+0x62a/0x810 fs/ioctl.c:696
>>    [<000000000cebb5d9>] ksys_ioctl+0x86/0xb0 fs/ioctl.c:713
>>    [<000000001630008a>] __do_sys_ioctl fs/ioctl.c:720 [inline]
>>    [<000000001630008a>] __se_sys_ioctl fs/ioctl.c:718 [inline]
>>    [<000000001630008a>] __x64_sys_ioctl+0x1e/0x30 fs/ioctl.c:718
>>    [<00000000c62091e3>] do_syscall_64+0x76/0x1a0
>>    arch/x86/entry/common.c:301
>>    [<000000005c213625>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>    ---
>>    This bug is generated by a bot. It may contain errors.
>>    See https://goo.gl/tpsmEJ <https://goo.gl/tpsmEJ> for more
>>    information about syzbot.
>>    syzbot engineers can be reached at syzk...@googlegroups.com.
>>    syzbot will keep track of this bug report. See:
>>    https://goo.gl/tpsmEJ#status <https://goo.gl/tpsmEJ#status> for how
>>    to communicate with syzbot.
>>    syzbot can test patches for this bug, for details see:
>>    https://goo.gl/tpsmEJ#testing-patches
>>    <https://goo.gl/tpsmEJ#testing-patches>
>> -- 
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>> To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/d71a274f-fdeb-4da1-898e-06f6944e04dan%40googlegroups.com <https://groups.google.com/d/msgid/syzkaller-bugs/d71a274f-fdeb-4da1-898e-06f6944e04dan%40googlegroups.com?utm_medium=email&utm_source=footer>.
> 
> The reason of this memory leak is tty_ldisc_receive_buf() and tiocsti()
> can access the h4->rx_skb concurrently by calling
> hci_uart_tty_receive(), so the rx_skb be overwritten without
> deallocating. There used to be an spin_lock in hci_uart_tty_receive(),
> but it was removed by commit 7649ffaff1cfe(Bluetooth: Remove useless
> rx_lock spinlock).

I don’t have that commit in my Linus’ tree. Where is it?

> The commit message claims that hci_uart_tty_receive() was only called by
> flush_to_ldisc(), but it seems incorrect.

That seems to be a larger problem in the TTY layer if its contract with its users have changed.

Regards

Marcel