Hello linux-usb,
We've hit a USB use-after-free on Stratus HW during device removal tests.
We're running fio disk I/O to a scsi disk hanging off USB when the USB
controller is hotplug removed. This crash is very consistent (usually the
first device pull during testing). Without I/O, it may take days to
encounter.
general protection fault: 0000 [#1] SMP
...
CPU: 35 PID: 19626 Comm: kworker/u97:0 Tainted: PF W O-------------- 3.10.0-210.el7.dev02.x86_64 #1
Hardware name: Stratus ftServer 6800/G7LYY, BIOS BIOS Version 8.0:30 11/12/2014
Workqueue: scsi_tmf_872 scmd_eh_abort_handler
task: ffff88031bd91960 ti: ffff880981318000 task.ti: ffff880981318000
RIP: 0010:[<ffffffff812d5e2d>] [<ffffffff812d5e2d>] kobject_put+0xd/0x60
RSP: 0018:ffff88098131bd28 EFLAGS: 00010002
RAX: 0000000000000000 RBX: 6b6b6b6b6b6b6c0b RCX: 00000001002f0009
RDX: 000000000000002f RSI: ffffea0015719800 RDI: 6b6b6b6b6b6b6c0b
RBP: ffff88098131bd30 R08: ffff88055c6622f0 R09: 00000001002f0008
R10: ffff88085f407a80 R11: ffffffff81450503 R12: ffff8804bab6d248
R13: 00000000ffffff98 R14: 0000000000000086 R15: 0000000000000c20
FS: 0000000000000000(0000) GS:ffff88085fce0000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f2ebb5d6008 CR3: 0000001038dc5000 CR4: 00000000001407e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Stack:
0000000000000000 ffff88098131bd40 ffffffff813cd327 ffff88098131bd50
ffffffff8140a65a ffff88098131bd78 ffffffff81416795 0000000000000000
ffff880414791968 ffff880414791978 ffff88098131bd88 ffffffff814175f6
Call Trace:
[<ffffffff813cd327>] put_device+0x17/0x20
[<ffffffff8140a65a>] usb_put_dev+0x1a/0x20
[<ffffffff81416795>] usb_hcd_unlink_urb+0x65/0xe0
[<ffffffff814175f6>] usb_unlink_urb+0x26/0x50
[<ffffffff81418e92>] usb_sg_cancel+0x82/0xe0
[<ffffffffa0074e71>] usb_stor_stop_transport+0x31/0x50 [usb_storage]
[<ffffffffa0073b8d>] command_abort+0xcd/0xe0 [usb_storage]
[<ffffffff813f51ef>] scmd_eh_abort_handler+0xbf/0x480
[<ffffffff8108f06b>] process_one_work+0x17b/0x470
[<ffffffff8108fe4b>] worker_thread+0x11b/0x400
[<ffffffff8108fd30>] ? rescuer_thread+0x400/0x400
[<ffffffff8109722f>] kthread+0xcf/0xe0
[<ffffffff81097160>] ? kthread_create_on_node+0x140/0x140
[<ffffffff8161387c>] ret_from_fork+0x7c/0xb0
[<ffffffff81097160>] ? kthread_create_on_node+0x140/0x140
from another crash, we know that the URB itself has been freed:
crash> struct -o urb | grep SIZE
SIZE: 0xc0
crash> p 0xc0/8
$2 = 0x18
crash> rd ffff880846df9248 0x18
ffff880846df9248: 6b6b6b6b6b6b6b6b 6b6b6b6b6b6b6b6b kkkkkkkkkkkkkkkk
ffff880846df9258: 6b6b6b6b6b6b6b6b 6b6b6b6b6b6b6b6b kkkkkkkkkkkkkkkk
ffff880846df9268: 6b6b6b6b6b6b6b6b 6b6b6b6b6b6b6b6b kkkkkkkkkkkkkkkk
ffff880846df9278: 6b6b6b6b6b6b6b6b 6b6b6b6b6b6b6b6b kkkkkkkkkkkkkkkk
ffff880846df9288: 6b6b6b6b6b6b6b6b 6b6b6b6b6b6b6b6b kkkkkkkkkkkkkkkk
ffff880846df9298: 6b6b6b6b6b6b6b6b 6b6b6b6b6b6b6b6b kkkkkkkkkkkkkkkk
ffff880846df92a8: 6b6b6b6b6b6b6b6b 6b6b6b6b6b6b6b6b kkkkkkkkkkkkkkkk
ffff880846df92b8: 6b6b6b6b6b6b6b6b 6b6b6b6b6b6b6b6b kkkkkkkkkkkkkkkk
ffff880846df92c8: 6b6b6b6b6b6b6b6b 6b6b6b6b6b6b6b6b kkkkkkkkkkkkkkkk
ffff880846df92d8: 6b6b6b6b6b6b6b6b 6b6b6b6b6b6b6b6b kkkkkkkkkkkkkkkk
ffff880846df92e8: 6b6b6b6b6b6b6b6b 6b6b6b6b6b6b6b6b kkkkkkkkkkkkkkkk
ffff880846df92f8: 6b6b6b6b6b6b6b6b a56b6b6b6b6b6b6b kkkkkkkkkkkkkkk.
but the underlying usb_device->device is still present:
crash> struct usb_device ffff88084fd22e68
...
dev = {
parent = 0xffff881050c3d418,
p = 0xffff88084ff27ae8,
kobj = {
name = 0xffff88084ff071e0 "6-1",
entry = {
next = 0xffff88084ff09568,
prev = 0xffff88084ff09000
},
parent = 0xffff881050c3d428,
kset = 0xffff8808540dc9f0,
ktype = 0xffffffff819cc220 <device_ktype>,
sd = 0xffff88084ff1b8b8,
kref = {
refcount = {
counter = 0x8
}
},
state_initialized = 0x1,
state_in_sysfs = 0x1,
state_add_uevent_sent = 0x1,
state_remove_uevent_sent = 0x0,
uevent_suppress = 0x0
},
...
I added trace printing to usb_{alloc_urb,get_urb,free_urb} and urb_destroy
showing the URB and the calling function, then crashed again:
... snip ...
usb-storage-687 [000] 350.013212: bprint: usb_alloc_urb : JL: usb_sg_init+0xe1 -> usb_alloc_urb(0xffff8808489b0a28)
usb-storage-687 [000] 350.013212: bprint: usb_get_urb : JL: usb_hcd_submit_urb+0x3b -> usb_get_urb(0xffff8808489b0a28)
kworker/u97:2-703 [006] 380.656791: bprint: usb_free_urb : JL: __usb_hcd_giveback_urb -> usb_free_urb(0xffff8808489b0a28)
usb-storage-687 [000] 380.656793: bprint: usb_free_urb : JL: sg_clean+0x33 -> usb_free_urb(0xffff8808489b0a28)
usb-storage-687 [000] 380.656794: bprint: urb_destroy : JL: usb_free_urb+0x40 -> urb_destroy(0xffff8808489b0a28)
crash> bt 703
PID: 703 TASK: ffff8808497f8000 CPU: 6 COMMAND: "kworker/u97:2"
#0 [ffff8808497f7c10] die at ffffffff8101736b
#1 [ffff8808497f7c40] do_general_protection at ffffffff8160be4e
#2 [ffff8808497f7c70] general_protection at ffffffff8160b768
[exception RIP: kobject_put+0xd]
RIP: ffffffff812d69dd RSP: ffff8808497f7d28 RFLAGS: 00010002
RAX: 0000000000000000 RBX: 6b6b6b6b6b6b6c0b RCX: dead000000200200
RDX: ffff88085f400390 RSI: 0000000000000047 RDI: 6b6b6b6b6b6b6c0b
RBP: ffff8808497f7d30 R8: ffff88085f400390 R9: 00000001002f002e
R10: ffff88085f407a80 R11: ffffffff81450e03 R12: ffff8808489b0a28
R13: 00000000ffffff98 R14: 0000000000000086 R15: 0000000000000c20
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
#3 [ffff8808497f7d38] put_device at ffffffff813cdc57
#4 [ffff8808497f7d48] usb_put_dev at ffffffff8140afda
#5 [ffff8808497f7d58] usb_hcd_unlink_urb at ffffffff81417115
#6 [ffff8808497f7d80] usb_unlink_urb at ffffffff814180d6
#7 [ffff8808497f7d90] usb_sg_cancel at ffffffff81419792
#8 [ffff8808497f7dc0] usb_stor_stop_transport at ffffffffa00a9e71 [usb_storage]
#9 [ffff8808497f7dd8] command_abort at ffffffffa00a8b8d [usb_storage]
#10 [ffff8808497f7df8] scmd_eh_abort_handler at ffffffff813f5b5f
#11 [ffff8808497f7e20] process_one_work at ffffffff8108f0ab
#12 [ffff8808497f7e68] worker_thread at ffffffff8108fe8b
#13 [ffff8808497f7ec8] kthread at ffffffff8109726f
#14 [ffff8808497f7f50] ret_from_fork at ffffffff81613cbc
PID: 687 TASK: ffff88084c92a610 CPU: 0 COMMAND: "usb-storage"
[exception RIP: _raw_spin_lock_irq+0x38]
RIP: ffffffff8160b1d8 RSP: ffff88084cc23da0 RFLAGS: 00000002
RAX: 0000000000001d66 RBX: ffff88104cea1888 RCX: 0000000000008160
RDX: 0000000000008162 RSI: 0000000000008162 RDI: ffff88104cea1198
RBP: ffff88084cc23da0 R8: 0000000000001000 R9: 0000000100300023
R10: ffff88085f404240 R11: ffffffff81418e39 R12: ffff88084a878900
R13: ffff88104cea19f8 R14: 0000000000000003 R15: 0000000000000000
CS: 0010 SS: 0018
#0 [ffff88084cc23da8] usb_stor_invoke_transport at ffffffffa00a9fe2 [usb_storage]
#1 [ffff88084cc23e58] usb_stor_transparent_scsi_command at ffffffffa00a8c6e [usb_storage]
#2 [ffff88084cc23e68] usb_stor_control_thread at ffffffffa00ab6d8 [usb_storage]
#3 [ffff88084cc23ec8] kthread at ffffffff8109726f
#4 [ffff88084cc23f50] ret_from_fork at ffffffff81613cbc
It looks like usb_hcd_unlink_urb takes a reference out on the underlying
device but not the URB, which in our test case consistently gets freed
just before usb_hcd_unlink_urb tries to return a reference on urb->device.
Maybe the URB is a reference count short when usb_hcd_unlink_urb calls
unlink1? Somewhere usb-storage missed taking out a ref?
A tourniquet hack-patch follows (probably inside out, as the URB should stay
intact while usb_hcd_unlink_urb does its thing) and has been running a
little over 30 surprise device removals under I/O without incident.
Any better suggestions?
-- Joe
-->8-- -->8-- -->8--
diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 11cee55ae397..3a4ccc13f6a8 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -1624,8 +1624,10 @@ int usb_hcd_unlink_urb (struct urb *urb, int status)
/* Prevent the device and bus from going away while
* the unlink is carried out. If they are already gone
* then urb->use_count must be 0, since disconnected
- * devices can't have any active URBs.
+ * devices can't have any active URBs. Nail down the
+ * URB while we're at it, too.
*/
+ usb_get_urb(urb);
spin_lock_irqsave(&hcd_urb_unlink_lock, flags);
if (atomic_read(&urb->use_count) > 0) {
retval = 0;
@@ -1643,6 +1645,7 @@ int usb_hcd_unlink_urb (struct urb *urb, int status)
else if (retval != -EIDRM && retval != -EBUSY)
dev_dbg(&urb->dev->dev, "hcd_unlink_urb %p fail %d\n",
urb, retval);
+ usb_put_urb(urb);
return retval;
}
--
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