Re: [PATCH V2 2/2] [BUGFIX] virtio/console: Add pipe_lock/unlock for splice_write

[Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>]

(2013/07/19 18:19), Yoshihiro YUNOMAE wrote:
> Add pipe_lock/unlock for splice_write to avoid oops by following competition:
> 
> (1) An application gets fds of a trace buffer, virtio-serial, pipe.
> (2) The application does fork()
> (3) The processes execute splice_read(trace buffer) and
>     splice_write(virtio-serial) via same pipe.
> 
>         <parent>                   <child>
>   get fds of a trace buffer,
>          virtio-serial, pipe
>           |
>         fork()----------create--------+
>           |                           |
>       splice(read)                    |           ---+
>       splice(write)                   |              +-- no competition
>           |                       splice(read)       |
>           |                       splice(write)   ---+
>           |                           |
>       splice(read)                    |
>       splice(write)               splice(read)    ------ competition
>           |                       splice(write)
> 
> Two processes share a pipe_inode_info structure. If the child execute
> splice(read) when the parent tries to execute splice(write), the
> structure can be broken. Existing virtio-serial driver does not get
> lock for the structure in splice_write, so this competition will induce
> oops.
> 
> <oops messages>
>  BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
>  IP: [<ffffffff811a6b5f>] splice_from_pipe_feed+0x6f/0x130
>  PGD 7223e067 PUD 72391067 PMD 0
>  Oops: 0000 [#1] SMP
>  Modules linked in: lockd bnep bluetooth rfkill sunrpc ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables snd_hda_intel snd_hda_codec snd_hwdep snd_pcm snd_page_alloc snd_timer snd soundcore pcspkr virtio_net virtio_balloon i2c_piix4 i2c_core microcode uinput floppy
>  CPU: 0 PID: 1072 Comm: compete-test Not tainted 3.10.0ws+ #55
>  Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
>  task: ffff880071b98000 ti: ffff88007b55e000 task.ti: ffff88007b55e000
>  RIP: 0010:[<ffffffff811a6b5f>]  [<ffffffff811a6b5f>] splice_from_pipe_feed+0x6f/0x130
>  RSP: 0018:ffff88007b55fd78  EFLAGS: 00010287
>  RAX: 0000000000000000 RBX: ffff88007b55fe20 RCX: 0000000000000000
>  RDX: 0000000000001000 RSI: ffff88007a95ba30 RDI: ffff880036f9e6c0
>  RBP: ffff88007b55fda8 R08: 00000000000006ec R09: ffff880077626708
>  R10: 0000000000000003 R11: ffffffff8139ca59 R12: ffff88007a95ba30
>  R13: 0000000000000000 R14: ffffffff8139dd00 R15: ffff880036f9e6c0
>  FS:  00007f2e2e3a0740(0000) GS:ffff88007fc00000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>  CR2: 0000000000000018 CR3: 0000000071bd1000 CR4: 00000000000006f0
>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>  Stack:
>   ffffffff8139ca59 ffff88007b55fe20 ffff880036f9e6c0 ffffffff8139dd00
>   ffff8800776266c0 ffff880077626708 ffff88007b55fde8 ffffffff811a6e8e
>   ffff88007b55fde8 ffffffff8139ca59 ffff880036f9e6c0 ffff88007b55fe20
>  Call Trace:
>   [<ffffffff8139ca59>] ? alloc_buf.isra.13+0x39/0xb0
>   [<ffffffff8139dd00>] ? virtcons_restore+0x100/0x100
>   [<ffffffff811a6e8e>] __splice_from_pipe+0x7e/0x90
>   [<ffffffff8139ca59>] ? alloc_buf.isra.13+0x39/0xb0
>   [<ffffffff8139d739>] port_fops_splice_write+0xe9/0x140
>   [<ffffffff8127a3f4>] ? selinux_file_permission+0xc4/0x120
>   [<ffffffff8139d650>] ? wait_port_writable+0x1b0/0x1b0
>   [<ffffffff811a6fe0>] do_splice_from+0xa0/0x110
>   [<ffffffff811a951f>] SyS_splice+0x5ff/0x6b0
>   [<ffffffff8161facf>] tracesys+0xdd/0xe2
>  Code: 49 8b 87 80 00 00 00 4c 8d 24 d0 8b 53 04 41 8b 44 24 0c 4d 8b 6c 24 10 39 d0 89 03 76 02 89 13 49 8b 44 24 10 4c 89 e6 4c 89 ff <ff> 50 18 85 c0 0f 85 aa 00 00 00 48 89 da 4c 89 e6 4c 89 ff 41
>  RIP  [<ffffffff811a6b5f>] splice_from_pipe_feed+0x6f/0x130
>   RSP <ffff88007b55fd78>
>  CR2: 0000000000000018
>  ---[ end trace 24572beb7764de59 ]---
> 
> V2: Fix a locking problem for error

Thanks, this looks good for me.

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

> 
> Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
> Cc: Amit Shah <amit.shah@redhat.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  drivers/char/virtio_console.c |   20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index 8722656..8a15af3 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -936,16 +936,21 @@ static ssize_t port_fops_splice_write(struct pipe_inode_info *pipe,
>  	 * pipe->nrbufs == 0 means there are no data to transfer,
>  	 * so this returns just 0 for no data.
>  	 */
> -	if (!pipe->nrbufs)
> -		return 0;
> +	pipe_lock(pipe);
> +	if (!pipe->nrbufs) {
> +		ret = 0;
> +		goto error_out;
> +	}
>  
>  	ret = wait_port_writable(port, filp->f_flags & O_NONBLOCK);
>  	if (ret < 0)
> -		return ret;
> +		goto error_out;
>  
>  	buf = alloc_buf(port->out_vq, 0, pipe->nrbufs);
> -	if (!buf)
> -		return -ENOMEM;
> +	if (!buf) {
> +		ret = -ENOMEM;
> +		goto error_out;
> +	}
>  
>  	sgl.n = 0;
>  	sgl.len = 0;
> @@ -953,12 +958,17 @@ static ssize_t port_fops_splice_write(struct pipe_inode_info *pipe,
>  	sgl.sg = buf->sg;
>  	sg_init_table(sgl.sg, sgl.size);
>  	ret = __splice_from_pipe(pipe, &sd, pipe_to_sg);
> +	pipe_unlock(pipe);
>  	if (likely(ret > 0))
>  		ret = __send_to_port(port, buf->sg, sgl.n, sgl.len, buf, true);
>  
>  	if (unlikely(ret <= 0))
>  		free_buf(buf, true);
>  	return ret;
> +
> +error_out:
> +	pipe_unlock(pipe);
> +	return ret;
>  }
>  
>  static unsigned int port_fops_poll(struct file *filp, poll_table *wait)
> 
> 


-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com