blktrace: fix debugfs use after free
On commit 6ac93117ab00 ("blktrace: use existing disk debugfs directory")
merged on v4.12 Omar fixed the original blktrace code for request-based
drivers (multiqueue). This however left in place a possible crash, if you
happen to abuse blktrace while racing to remove / add a device.
We used to use asynchronous removal of the request_queue, and with that
the issue was easier to reproduce. Now that we have reverted to
synchronous removal of the request_queue, the issue is still possible to
reproduce, its however just a bit more difficult.
We essentially run two instances of break-blktrace which add/remove
a loop device, and setup a blktrace and just never tear the blktrace
down. We do this twice in parallel. This is easily reproduced with the
script run_0004.sh from break-blktrace [0].
We can end up with two types of panics each reflecting where we
race, one a failed blktrace setup:
[ 252.426751] debugfs: Directory 'loop0' with parent 'block' already present!
[ 252.432265] BUG: kernel NULL pointer dereference, address: 00000000000000a0
[ 252.436592] #PF: supervisor write access in kernel mode
[ 252.439822] #PF: error_code(0x0002) - not-present page
[ 252.442967] PGD 0 P4D 0
[ 252.444656] Oops: 0002 [#1] SMP NOPTI
[ 252.446972] CPU: 10 PID: 1153 Comm: break-blktrace Tainted: G E 5.7.0-rc2-next-20200420+ #164
[ 252.452673] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
[ 252.456343] RIP: 0010:down_write+0x15/0x40
[ 252.458146] Code: eb ca e8 ae 22 8d ff cc cc cc cc cc cc cc cc cc cc cc cc
cc cc 0f 1f 44 00 00 55 48 89 fd e8 52 db ff ff 31 c0 ba 01 00
00 00 <f0> 48 0f b1 55 00 75 0f 48 8b 04 25 c0 8b 01 00 48 89
45 08 5d
[ 252.463638] RSP: 0018:ffffa626415abcc8 EFLAGS: 00010246
[ 252.464950] RAX: 0000000000000000 RBX: ffff958c25f0f5c0 RCX: ffffff8100000000
[ 252.466727] RDX: 0000000000000001 RSI: ffffff8100000000 RDI: 00000000000000a0
[ 252.468482] RBP: 00000000000000a0 R08: 0000000000000000 R09: 0000000000000001
[ 252.470014] R10: 0000000000000000 R11: ffff958d1f9227ff R12: 0000000000000000
[ 252.471473] R13: ffff958c25ea5380 R14: ffffffff8cce15f1 R15: 00000000000000a0
[ 252.473346] FS: 00007f2e69dee540(0000) GS:ffff958c2fc80000(0000) knlGS:0000000000000000
[ 252.475225] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 252.476267] CR2: 00000000000000a0 CR3: 0000000427d10004 CR4: 0000000000360ee0
[ 252.477526] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 252.478776] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 252.479866] Call Trace:
[ 252.480322] simple_recursive_removal+0x4e/0x2e0
[ 252.481078] ? debugfs_remove+0x60/0x60
[ 252.481725] ? relay_destroy_buf+0x77/0xb0
[ 252.482662] debugfs_remove+0x40/0x60
[ 252.483518] blk_remove_buf_file_callback+0x5/0x10
[ 252.484328] relay_close_buf+0x2e/0x60
[ 252.484930] relay_open+0x1ce/0x2c0
[ 252.485520] do_blk_trace_setup+0x14f/0x2b0
[ 252.486187] __blk_trace_setup+0x54/0xb0
[ 252.486803] blk_trace_ioctl+0x90/0x140
[ 252.487423] ? do_sys_openat2+0x1ab/0x2d0
[ 252.488053] blkdev_ioctl+0x4d/0x260
[ 252.488636] block_ioctl+0x39/0x40
[ 252.489139] ksys_ioctl+0x87/0xc0
[ 252.489675] __x64_sys_ioctl+0x16/0x20
[ 252.490380] do_syscall_64+0x52/0x180
[ 252.491032] entry_SYSCALL_64_after_hwframe+0x44/0xa9
And the other on the device removal:
[ 128.528940] debugfs: Directory 'loop0' with parent 'block' already present!
[ 128.615325] BUG: kernel NULL pointer dereference, address: 00000000000000a0
[ 128.619537] #PF: supervisor write access in kernel mode
[ 128.622700] #PF: error_code(0x0002) - not-present page
[ 128.625842] PGD 0 P4D 0
[ 128.627585] Oops: 0002 [#1] SMP NOPTI
[ 128.629871] CPU: 12 PID: 544 Comm: break-blktrace Tainted: G E 5.7.0-rc2-next-20200420+ #164
[ 128.635595] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
[ 128.640471] RIP: 0010:down_write+0x15/0x40
[ 128.643041] Code: eb ca e8 ae 22 8d ff cc cc cc cc cc cc cc cc cc cc cc cc
cc cc 0f 1f 44 00 00 55 48 89 fd e8 52 db ff ff 31 c0 ba 01 00
00 00 <f0> 48 0f b1 55 00 75 0f 65 48 8b 04 25 c0 8b 01 00 48 89
45 08 5d
[ 128.650180] RSP: 0018:ffffa9c3c05ebd78 EFLAGS: 00010246
[ 128.651820] RAX: 0000000000000000 RBX: ffff8ae9a6370240 RCX: ffffff8100000000
[ 128.653942] RDX: 0000000000000001 RSI: ffffff8100000000 RDI: 00000000000000a0
[ 128.655720] RBP: 00000000000000a0 R08: 0000000000000002 R09: ffff8ae9afd2d3d0
[ 128.657400] R10: 0000000000000056 R11: 0000000000000000 R12: 0000000000000000
[ 128.659099] R13: 0000000000000000 R14: 0000000000000003 R15: 00000000000000a0
[ 128.660500] FS: 00007febfd995540(0000) GS:ffff8ae9afd00000(0000) knlGS:0000000000000000
[ 128.662204] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 128.663426] CR2: 00000000000000a0 CR3: 0000000420042003 CR4: 0000000000360ee0
[ 128.664776] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 128.666022] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 128.667282] Call Trace:
[ 128.667801] simple_recursive_removal+0x4e/0x2e0
[ 128.668663] ? debugfs_remove+0x60/0x60
[ 128.669368] debugfs_remove+0x40/0x60
[ 128.669985] blk_trace_free+0xd/0x50
[ 128.670593] __blk_trace_remove+0x27/0x40
[ 128.671274] blk_trace_shutdown+0x30/0x40
[ 128.671935] blk_release_queue+0x95/0xf0
[ 128.672589] kobject_put+0xa5/0x1b0
[ 128.673188] disk_release+0xa2/0xc0
[ 128.673786] device_release+0x28/0x80
[ 128.674376] kobject_put+0xa5/0x1b0
[ 128.674915] loop_remove+0x39/0x50 [loop]
[ 128.675511] loop_control_ioctl+0x113/0x130 [loop]
[ 128.676199] ksys_ioctl+0x87/0xc0
[ 128.676708] __x64_sys_ioctl+0x16/0x20
[ 128.677274] do_syscall_64+0x52/0x180
[ 128.677823] entry_SYSCALL_64_after_hwframe+0x44/0xa9
The common theme here is:
debugfs: Directory 'loop0' with parent 'block' already present
This crash happens because of how blktrace uses the debugfs directory
where it places its files. Upon init we always create the same directory
which would be needed by blktrace but we only do this for make_request
drivers (multiqueue) block drivers, but never for request-based block
drivers. Furthermore, that directory is only created on init for the
entire disk. This means that if you use blktrace on a partition, we'll
always be creating a new directory regardless of whether or not you
are doing blktrace on a make_request driver (multiqueue) or a
request-based block drivers.
These directory creations are only associated with a path, and so
when a debugfs_remove() is called it removes everything in its way.
A device removal will remove all blktrace files, and so if a blktrace
is still present a cleanup of blktrace files later will end up trying
to remove dentries pointing to NULL.
We can fix the UAF by using a debugfs directory which moving forward
will always be accessible if debugfs is enabled for both make_request
drivers (multiqueue) and request-based block drivers, *and* for all
partitions upon creation. This ensures that removal of the directories
only happens on device removal and removes the race of the files
underneath an active blktrace.
We special-case a solution for scsi-generic as well which got blktrace
support added by Christof via commit 6da127ad0918 ("blktrace: Add
blktrace ioctls to SCSI generic devices") so upstream since v2.6.25.
scsi-generic drives use a character device, however behind the scenes
we have a scsi device with a request_queue. How this is used varies
by class of driver (TYPE_DISK, TYPE_TAPE, etc). We simply create its
a scsi-generic dedicated debugfs_dir and have blktrace use that when
this interface is used.
This goes tested with:
o nvme partitions
o ISCSI with tgt, and blktracing against scsi-generic with:
o block
o tape
o cdrom
o media changer
o blktests
This patch is part of the work which disputes the severity of
CVE-2019-19770 which shows this issue is not a core debugfs issue, but
a misuse of debugfs within blktace.
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Nicolai Stange <nstange@suse.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
Cc: yu kuai <yukuai3@huawei.com>
Reported-by: syzbot+603294af2d01acfdd6da@syzkaller.appspotmail.com
Fixes: 6ac93117ab00 ("blktrace: use existing disk debugfs directory")
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
10 files changed
