[PATCH 4.12 08/43] USB: core: Avoid race of async_completed() w/ usbdev_release()

Greg Kroah-Hartman
2017-09-08T13:22:41Z

From: Douglas Anderson <dianders@chromium.org>

commit ed62ca2f4f51c17841ea39d98c0c409cb53a3e10 upstream.

While running reboot tests w/ a specific set of USB devices (and
slub_debug enabled), I found that once every few hours my device would
be crashed with a stack that looked like this:

[ 14.012445] BUG: spinlock bad magic on CPU#0, modprobe/2091
[ 14.012460] lock: 0xffffffc0cb055978, .magic: ffffffc0, .owner: cryption contexts: %lu/%lu
[ 14.012460] /1025536097, .owner_cpu: 0
[ 14.012466] CPU: 0 PID: 2091 Comm: modprobe Not tainted 4.4.79 #352
[ 14.012468] Hardware name: Google Kevin (DT)
[ 14.012471] Call trace:
[ 14.012483] [<....>] dump_backtrace+0x0/0x160
[ 14.012487] [<....>] show_stack+0x20/0x28
[ 14.012494] [<....>] dump_stack+0xb4/0xf0
[ 14.012500] [<....>] spin_dump+0x8c/0x98
[ 14.012504] [<....>] spin_bug+0x30/0x3c
[ 14.012508] [<....>] do_raw_spin_lock+0x40/0x164
[ 14.012515] [<....>] _raw_spin_lock_irqsave+0x64/0x74
[ 14.012521] [<....>] __wake_up+0x2c/0x60
[ 14.012528] [<....>] async_completed+0x2d0/0x300
[ 14.012534] [<....>] __usb_hcd_giveback_urb+0xc4/0x138
[ 14.012538] [<....>] usb_hcd_giveback_urb+0x54/0xf0
[ 14.012544] [<....>] xhci_irq+0x1314/0x1348
[ 14.012548] [<....>] usb_hcd_irq+0x40/0x50
[ 14.012553] [<....>] handle_irq_event_percpu+0x1b4/0x3f0
[ 14.012556] [<....>] handle_irq_event+0x4c/0x7c
[ 14.012561] [<....>] handle_fasteoi_irq+0x158/0x1c8
[ 14.012564] [<....>] generic_handle_irq+0x30/0x44
[ 14.012568] [<....>] __handle_domain_irq+0x90/0xbc
[ 14.012572] [<....>] gic_handle_irq+0xcc/0x18c

Investigation using kgdb() found that the wait queue that was passed
into wake_up() had been freed (it was filled with slub_debug poison).

I analyzed and instrumented the code and reproduced. My current
belief is that this is happening:

1. async_completed() is called (from IRQ). Moves "as" onto the
completed list.
2. On another CPU, proc_reapurbnonblock_compat() calls
async_getcompleted(). Blocks on spinlock.
3. async_completed() releases the lock; keeps running; gets blocked
midway through wake_up().
4. proc_reapurbnonblock_compat() => async_getcompleted() gets the
lock; removes "as" from completed list and frees it.
5. usbdev_release() is called. Frees "ps".
6. async_completed() finally continues running wake_up(). ...but
wake_up() has a pointer to the freed "ps".

The instrumentation that led me to believe this was based on adding
some trace_printk() calls in a select few functions and then using
kdb's "ftdump" at crash time. The trace follows (NOTE: in the trace
below I cheated a little bit and added a udelay(1000) in
async_completed() after releasing the spinlock because I wanted it to
trigger quicker):

<...>-2104 0d.h2 13759034us!: async_completed at start: as=ffffffc0cc638200
mtpd-2055 3.... 13759356us : async_getcompleted before spin_lock_irqsave
mtpd-2055 3d..1 13759362us : async_getcompleted after list_del_init: as=ffffffc0cc638200
mtpd-2055 3.... 13759371us+: proc_reapurbnonblock_compat: free_async(ffffffc0cc638200)
mtpd-2055 3.... 13759422us+: async_getcompleted before spin_lock_irqsave
mtpd-2055 3.... 13759479us : usbdev_release at start: ps=ffffffc0cc042080
mtpd-2055 3.... 13759487us : async_getcompleted before spin_lock_irqsave
mtpd-2055 3.... 13759497us!: usbdev_release after kfree(ps): ps=ffffffc0cc042080
<...>-2104 0d.h2 13760294us : async_completed before wake_up(): as=ffffffc0cc638200

To fix this problem we can just move the wake_up() under the ps->lock.
There should be no issues there that I'm aware of.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/core/devio.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -623,6 +623,8 @@ static void async_completed(struct urb *
if (as->status < 0 && as->bulk_addr && as->status != -ECONNRESET &&
as->status != -ENOENT)
cancel_bulk_urbs(ps, as->bulk_addr);
+
+ wake_up(&ps->wait);
spin_unlock(&ps->lock);

if (signr) {
@@ -630,8 +632,6 @@ static void async_completed(struct urb *
put_pid(pid);
put_cred(cred);
}
-
- wake_up(&ps->wait);
}

static void destroy_async(struct usb_dev_state *ps, struct list_head *list)