Re: memory leak in h4_recv_buf

[Phi Nguyen]

On 7/29/2021 11:39 PM, Marcel Holtmann wrote:
> Hi Dan,
>
> > > > >    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...@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > > >    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...@xxxxxxxxxxxxxxxx.
> > > > >    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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> > > >
> > > > 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?
> >
> > There is a typo in the git hash.  It should be: 7649faff1cfe4 ("Bluetooth:
> > Remove useless rx_lock spinlock").
> >
> > > > 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.
> >
> > The tiocsti() function has an ancient comment which suggests that the
> > documentation has always been wrong.
> >
> > *      FIXME: may race normal receive processing
>
> so what are we suppose to do now? Fix this in TTY layer or try to revert this patch?
>
> And does it have to be spinlock or can we use a mutex? My knowledge of the TTY internal are limited and thus, I have no idea what we need to do here. However h4_recv_buf needs to be protected against concurrently calls.
>
> Regards
>
> Marcel
Hi Marcel,

So far, I have tested two fixes with syzbot
The first one is to bring the spin lock back to hci_uart_tty_receive().
The second one is to use tty_buffer_lock_exclusive() in tiocsti() (I 
based on the document in tty_buffer.c).
These two can work well with the syzbot.

Regards,
Phi