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Subject[PATCH 2/6] Input: uinput - avoid crash when sending FF request to device going away
Date
If FF request comes in while uinput device is going away,
uinput_request_send() will fail with -ENODEV, and uinput_request_submit()
will attempt to mark the slot as unused by calling uinput_request_done().
Unfortunately in this case we haven't initialized request->done completion
yet, and we get a crash:

[ 39.402036] BUG: spinlock bad magic on CPU#1, fftest/3108
[ 39.402046] lock: 0xffff88006a93bb00, .magic: 00000000, .owner: /39, .owner_cpu: 1217155072
[ 39.402055] CPU: 1 PID: 3108 Comm: fftest Tainted: G W 4.13.0+ #15
[ 39.402059] Hardware name: LENOVO 20HQS0EG02/20HQS0EG02, BIOS N1MET37W (1.22 ) 07/04/2017
[ 39.402064] 0000000000000086 f0fad82f3ceaa120 ffff88006a93b9a0 ffffffff9de941bb
[ 39.402077] ffff88026df8ae00 ffff88006a93bb00 ffff88006a93b9c0 ffffffff9dca62b7
[ 39.402088] ffff88006a93bb00 ffff88006a93baf8 ffff88006a93b9e0 ffffffff9dca62e7
[ 39.402099] Call Trace:
[ 39.402112] [<ffffffff9de941bb>] dump_stack+0x4d/0x63
[ 39.402123] [<ffffffff9dca62b7>] spin_dump+0x97/0x9c
[ 39.402130] [<ffffffff9dca62e7>] spin_bug+0x2b/0x2d
[ 39.402138] [<ffffffff9dca6373>] do_raw_spin_lock+0x28/0xfd
[ 39.402147] [<ffffffff9e3055cd>] _raw_spin_lock_irqsave+0x19/0x1f
[ 39.402154] [<ffffffff9dca05b7>] complete+0x1d/0x48
[ 39.402162] [<ffffffffc04f30af>] 0xffffffffc04f30af
[ 39.402167] [<ffffffffc04f468c>] 0xffffffffc04f468c
[ 39.402177] [<ffffffff9dd59c16>] ? __slab_free+0x22f/0x359
[ 39.402184] [<ffffffff9dcc13e9>] ? tk_clock_read+0xc/0xe
[ 39.402189] [<ffffffffc04f471f>] 0xffffffffc04f471f
[ 39.402195] [<ffffffff9dc9ffe5>] ? __wake_up+0x44/0x4b
[ 39.402200] [<ffffffffc04f3240>] ? 0xffffffffc04f3240
[ 39.402207] [<ffffffff9e0f57f3>] erase_effect+0xa1/0xd2
[ 39.402214] [<ffffffff9e0f58c6>] input_ff_flush+0x43/0x5c
[ 39.402219] [<ffffffffc04f32ad>] 0xffffffffc04f32ad
[ 39.402227] [<ffffffff9e0f174f>] input_flush_device+0x3d/0x51
[ 39.402234] [<ffffffff9e0f69ae>] evdev_flush+0x49/0x5c
[ 39.402243] [<ffffffff9dd62d6e>] filp_close+0x3f/0x65
[ 39.402253] [<ffffffff9dd7dcf7>] put_files_struct+0x66/0xc1
[ 39.402261] [<ffffffff9dd7ddeb>] exit_files+0x47/0x4e
[ 39.402270] [<ffffffff9dc6b329>] do_exit+0x483/0x969
[ 39.402278] [<ffffffff9dc73211>] ? recalc_sigpending_tsk+0x3d/0x44
[ 39.402285] [<ffffffff9dc6c7a2>] do_group_exit+0x42/0xb0
[ 39.402293] [<ffffffff9dc767e1>] get_signal+0x58d/0x5bf
[ 39.402300] [<ffffffff9dc03701>] do_signal+0x37/0x53e
[ 39.402307] [<ffffffff9e0f8401>] ? evdev_ioctl_handler+0xac8/0xb04
[ 39.402314] [<ffffffff9e0f8464>] ? evdev_ioctl+0x10/0x12
[ 39.402321] [<ffffffff9dd74cfa>] ? do_vfs_ioctl+0x42e/0x501
[ 39.402328] [<ffffffff9dc0170e>] prepare_exit_to_usermode+0x66/0x90
[ 39.402333] [<ffffffff9dc0181b>] syscall_return_slowpath+0xe3/0xec
[ 39.402339] [<ffffffff9e305b7b>] int_ret_from_sys_call+0x25/0x8f

While we could solve this by simply initializing the completion earlier, we
are better off rearranging the code a bit so we avoid calling complete() on
requests that we did not send out. This patch consolidates marking request
slots as free in one place (in uinput_request_submit(), the same place
where we acquire them) and having everyone else simply signal completion
of the requests.

Fixes: 00ce756ce53a ("Input: uinput - mark failed submission requests as free")
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
drivers/input/misc/uinput.c | 39 +++++++++++++++++++++------------------
1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
index 2cff40be8860..443151de90c6 100644
--- a/drivers/input/misc/uinput.c
+++ b/drivers/input/misc/uinput.c
@@ -98,14 +98,15 @@ static int uinput_request_reserve_slot(struct uinput_device *udev,
uinput_request_alloc_id(udev, request));
}

-static void uinput_request_done(struct uinput_device *udev,
- struct uinput_request *request)
+static void uinput_request_release_slot(struct uinput_device *udev,
+ unsigned int id)
{
/* Mark slot as available */
- udev->requests[request->id] = NULL;
- wake_up(&udev->requests_waitq);
+ spin_lock(&udev->requests_lock);
+ udev->requests[id] = NULL;
+ spin_unlock(&udev->requests_lock);

- complete(&request->done);
+ wake_up(&udev->requests_waitq);
}

static int uinput_request_send(struct uinput_device *udev,
@@ -138,20 +139,22 @@ static int uinput_request_send(struct uinput_device *udev,
static int uinput_request_submit(struct uinput_device *udev,
struct uinput_request *request)
{
- int error;
+ int retval;

- error = uinput_request_reserve_slot(udev, request);
- if (error)
- return error;
+ retval = uinput_request_reserve_slot(udev, request);
+ if (retval)
+ return retval;

- error = uinput_request_send(udev, request);
- if (error) {
- uinput_request_done(udev, request);
- return error;
- }
+ retval = uinput_request_send(udev, request);
+ if (retval)
+ goto out;

wait_for_completion(&request->done);
- return request->retval;
+ retval = request->retval;
+
+ out:
+ uinput_request_release_slot(udev, request->id);
+ return retval;
}

/*
@@ -169,7 +172,7 @@ static void uinput_flush_requests(struct uinput_device *udev)
request = udev->requests[i];
if (request) {
request->retval = -ENODEV;
- uinput_request_done(udev, request);
+ complete(&request->done);
}
}

@@ -957,7 +960,7 @@ static long uinput_ioctl_handler(struct file *file, unsigned int cmd,
}

req->retval = ff_up.retval;
- uinput_request_done(udev, req);
+ complete(&req->done);
goto out;

case UI_END_FF_ERASE:
@@ -973,7 +976,7 @@ static long uinput_ioctl_handler(struct file *file, unsigned int cmd,
}

req->retval = ff_erase.retval;
- uinput_request_done(udev, req);
+ complete(&req->done);
goto out;
}

--
2.14.1.581.gf28d330327-goog
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