[ 33/60] virtio/console: Add pipe_lock/unlock for splice_write

Greg Kroah-Hartman
2013-08-13T06:33:26Z

From: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>

commit 2b4fbf029dff5a28d9bf646346dea891ec43398a upstream.

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
V3: Add Reviewed-by lines and stable@ line in sign-off area

Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Amit Shah <amit.shah@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/char/virtio_console.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)

--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -936,16 +936,21 @@ static ssize_t port_fops_splice_write(st
* 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(st
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)