A userspace process holding a file descriptor to a virtio_blk device can
still invoke block_device_operations after hot unplug. This leads to a
use-after-free accessing vblk->vdev in virtblk_getgeo() when
ioctl(HDIO_GETGEO) is invoked:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000090
IP: [<ffffffffc00e5450>] virtio_check_driver_offered_feature+0x10/0x90 [virtio]
PGD 800000003a92f067 PUD 3a930067 PMD 0
Oops: 0000 [#1] SMP
CPU: 0 PID: 1310 Comm: hdio-getgeo Tainted: G OE ------------ 3.10.0-1062.el7.x86_64 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
task: ffff9be5fbfb8000 ti: ffff9be5fa890000 task.ti: ffff9be5fa890000
RIP: 0010:[<ffffffffc00e5450>] [<ffffffffc00e5450>] virtio_check_driver_offered_feature+0x10/0x90 [virtio]
RSP: 0018:ffff9be5fa893dc8 EFLAGS: 00010246
RAX: ffff9be5fc3f3400 RBX: ffff9be5fa893e30 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffff9be5fbc10b40
RBP: ffff9be5fa893dc8 R08: 0000000000000301 R09: 0000000000000301
R10: 0000000000000000 R11: 0000000000000000 R12: ffff9be5fdc24680
R13: ffff9be5fbc10b40 R14: ffff9be5fbc10480 R15: 0000000000000000
FS: 00007f1bfb968740(0000) GS:ffff9be5ffc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000090 CR3: 000000003a894000 CR4: 0000000000360ff0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
[<ffffffffc016ac37>] virtblk_getgeo+0x47/0x110 [virtio_blk]
[<ffffffff8d3f200d>] ? handle_mm_fault+0x39d/0x9b0
[<ffffffff8d561265>] blkdev_ioctl+0x1f5/0xa20
[<ffffffff8d488771>] block_ioctl+0x41/0x50
[<ffffffff8d45d9e0>] do_vfs_ioctl+0x3a0/0x5a0
[<ffffffff8d45dc81>] SyS_ioctl+0xa1/0xc0
A related problem is that virtblk_remove() leaks the vd_index_ida index
when something still holds a reference to vblk->disk during hot unplug.
This causes virtio-blk device names to be lost (vda, vdb, etc).
Fix these issues by protecting vblk->vdev with a mutex and reference
counting vblk so the vd_index_ida index can be removed in all cases.
Fixes: 48e4043d45 ("virtio: add virtio disk geometry feature")
Reported-by: Lance Digby <ldigby@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Link: https://lore.kernel.org/r/20200430140442.171016-1-stefanha@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
90b5feb8c4