(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@xxxxxxxxxxx> > > Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@xxxxxxxxxxx> > Cc: Amit Shah <amit.shah@xxxxxxxxxx> > Cc: Arnd Bergmann <arnd@xxxxxxxx> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > --- > 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@xxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html