Re: [PATCH V2 1/2] [BUGFIX] virtio/console: Quit from splice_write if pipe->nrbufs is 0

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

(2013/07/19 18:19), Yoshihiro YUNOMAE wrote:
> Quit from splice_write if pipe->nrbufs is 0 for avoiding oops in virtio-serial.
> 
> When an application was doing splice from a kernel buffer to virtio-serial on
> a guest, the application received signal(SIGINT). This situation will normally
> happen, but the kernel executed a kernel panic by oops as follows:
> 
>  BUG: unable to handle kernel paging request at ffff882071c8ef28
>  IP: [<ffffffff812de48f>] sg_init_table+0x2f/0x50
>  PGD 1fac067 PUD 0
>  Oops: 0000 [#1] SMP
>  Modules linked in: lockd sunrpc bnep bluetooth rfkill 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 microcode virtio_balloon virtio_net pcspkr soundcore i2c_piix4 i2c_core uinput floppy
>  CPU: 1 PID: 908 Comm: trace-cmd Not tainted 3.10.0+ #49
>  Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
>  task: ffff880071c64650 ti: ffff88007bf24000 task.ti: ffff88007bf24000
>  RIP: 0010:[<ffffffff812de48f>]  [<ffffffff812de48f>] sg_init_table+0x2f/0x50
>  RSP: 0018:ffff88007bf25dd8  EFLAGS: 00010286
>  RAX: 0000001fffffffe0 RBX: ffff882071c8ef28 RCX: 0000000000000000
>  RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff880071c8ef48
>  RBP: ffff88007bf25de8 R08: ffff88007fd15d40 R09: ffff880071c8ef48
>  R10: ffffea0001c71040 R11: ffffffff8139c555 R12: 0000000000000000
>  R13: ffff88007506a3c0 R14: ffff88007c862500 R15: ffff880071c8ef00
>  FS:  00007f0a3646c740(0000) GS:ffff88007fd00000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: ffff882071c8ef28 CR3: 000000007acbb000 CR4: 00000000000006e0
>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>  Stack:
>   ffff880071c8ef48 ffff88007bf25e20 ffff88007bf25e88 ffffffff8139d6fa
>   ffff88007bf25e28 ffffffff8127a3f4 0000000000000000 0000000000000000
>   ffff880071c8ef48 0000100000000000 0000000000000003 ffff88007bf25e08
>  Call Trace:
>   [<ffffffff8139d6fa>] port_fops_splice_write+0xaa/0x130
>   [<ffffffff8127a3f4>] ? selinux_file_permission+0xc4/0x120
>   [<ffffffff8139d650>] ? wait_port_writable+0x1b0/0x1b0
>   [<ffffffff811a6fe0>] do_splice_from+0xa0/0x110
>   [<ffffffff811a951f>] SyS_splice+0x5ff/0x6b0
>   [<ffffffff8161f8c2>] system_call_fastpath+0x16/0x1b
>  Code: c1 e2 05 48 89 e5 48 83 ec 10 4c 89 65 f8 41 89 f4 31 f6 48 89 5d f0 48 89 fb e8 8d ce ff ff 41 8d 44 24 ff 48 c1 e0 05 48 01 c3 <48> 8b 03 48 83 e0 fe 48 83 c8 02 48 89 03 48 8b 5d f0 4c 8b 65
>  RIP  [<ffffffff812de48f>] sg_init_table+0x2f/0x50
>   RSP <ffff88007bf25dd8>
>  CR2: ffff882071c8ef28
>  ---[ end trace 86323505eb42ea8f ]---
> 
> It seems to induce pagefault in sg_init_tabel() when pipe->nrbufs is equal to
> zero. This may happen in a following situation:
> 
> (1) The application normally does splice(read) from a kernel buffer, then does
>     splice(write) to virtio-serial.
> (2) The application receives SIGINT when is doing splice(read), so splice(read)
>     is failed by EINTR. However, the application does not finish the operation.
> (3) The application tries to do splice(write) without pipe->nrbufs.
> (4) The virtio-console driver tries to touch scatterlist structure sgl in
>     sg_init_table(), but the region is out of bound.
> 
> To avoid the case, a kernel should check whether pipe->nrbufs is empty or not
> when splice_write is executed in the virtio-console driver.

Thank you for fixing it :)

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 |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index 1b456fe..8722656 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -932,6 +932,13 @@ static ssize_t port_fops_splice_write(struct pipe_inode_info *pipe,
>  	if (is_rproc_serial(port->out_vq->vdev))
>  		return -EINVAL;
>  
> +	/*
> +	 * pipe->nrbufs == 0 means there are no data to transfer,
> +	 * so this returns just 0 for no data.
> +	 */
> +	if (!pipe->nrbufs)
> +		return 0;
> +
>  	ret = wait_port_writable(port, filp->f_flags & O_NONBLOCK);
>  	if (ret < 0)
>  		return ret;
> 
> 


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