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Subject[PATCH] hidraw: correctly deallocate memory on device disconnect
Hi Jiri,

This is mail is in regard to your commit for hidaw devices. We were seeing kernel crashes while connect and disconnect a hidraw device and we were hitting
rb tree corruption in vmalloc and kernel was crashing because of null pointer de-reference.
Later we figure out that was because the hid device disconnect is freeing memory which later got access by hidraw_read and hid_write.

commit df0cfd6990347c20ae031f3f34137cba274f1972
Author: Jiri Kosina <jkosina@suse.cz>
Date: Thu Nov 1 11:33:26 2012 +0100

HID: hidraw: put old deallocation mechanism in place

This basically reverts commit 4fe9f8e203fda. It causes multiple problems,
namely:


We found following commit by Ratan Nalumasu was helping in solving our issue
commit 4fe9f8e203fdad1524c04beb390f3c6099781ed9
Author: Ratan Nalumasu <ratan@google.com>
Date: Sat Sep 22 11:46:30 2012 -0700

HID: hidraw: don't deallocate memory when it is in use

When a device is unplugged, wait for all processes that have opened the device
to close before deallocating the device.


But there was a bug in Ratan's that commit which was causing slab memory corruption. We fixed that bug and now our issue solved. I can give evidence on issue.
The bug that was there in the commit that he was deleting list after words and feeing head of it before.
I am attaching the patch.


-regards
Manoj


-----------------------------------------------------------------------

diff --git a/drivers/hid/hidraw.c b/drivers/hid/hidraw.c
index a745163..612a655 100644
--- a/drivers/hid/hidraw.c
+++ b/drivers/hid/hidraw.c
@@ -113,7 +113,7 @@ static ssize_t hidraw_send_report(struct file *file, const char __user *buffer,
__u8 *buf;
int ret = 0;

- if (!hidraw_table[minor]) {
+ if (!hidraw_table[minor] || !hidraw_table[minor]->exist) {
ret = -ENODEV;
goto out;
}
@@ -261,7 +261,7 @@ static int hidraw_open(struct inode *inode, struct file *file)
}

mutex_lock(&minors_lock);
- if (!hidraw_table[minor]) {
+ if (!hidraw_table[minor] || !hidraw_table[minor]->exist) {
err = -ENODEV;
goto out_unlock;
}
@@ -302,39 +302,38 @@ static int hidraw_fasync(int fd, struct file *file, int on)
return fasync_helper(fd, file, on, &list->fasync);
}

+static void drop_ref(struct hidraw *hidraw, int exists_bit)
+{
+ if (exists_bit) {
+ hid_hw_close(hidraw->hid);
+ hidraw->exist = 0;
+ if (hidraw->open)
+ wake_up_interruptible(&hidraw->wait);
+ } else {
+ --hidraw->open;
+ }
+
+ if (!hidraw->open && !hidraw->exist) {
+ device_destroy(hidraw_class, MKDEV(hidraw_major, hidraw->minor));
+ hidraw_table[hidraw->minor] = NULL;
+ kfree(hidraw);
+ }
+}
+
static int hidraw_release(struct inode * inode, struct file * file)
{
unsigned int minor = iminor(inode);
- struct hidraw *dev;
struct hidraw_list *list = file->private_data;
- int ret;
- int i;

mutex_lock(&minors_lock);
- if (!hidraw_table[minor]) {
- ret = -ENODEV;
- goto unlock;
- }

list_del(&list->node);
- dev = hidraw_table[minor];
- if (!--dev->open) {
- if (list->hidraw->exist) {
- hid_hw_power(dev->hid, PM_HINT_NORMAL);
- hid_hw_close(dev->hid);
- } else {
- kfree(list->hidraw);
- }
- }
-
- for (i = 0; i < HIDRAW_BUFFER_SIZE; ++i)
- kfree(list->buffer[i].value);
kfree(list);
- ret = 0;
-unlock:
- mutex_unlock(&minors_lock);

- return ret;
+ drop_ref(hidraw_table[minor], 0);
+
+ mutex_unlock(&minors_lock);
+ return 0;
}

static long hidraw_ioctl(struct file *file, unsigned int cmd,
@@ -539,18 +538,9 @@ void hidraw_disconnect(struct hid_device *hid)
struct hidraw *hidraw = hid->hidraw;

mutex_lock(&minors_lock);
- hidraw->exist = 0;
-
- device_destroy(hidraw_class, MKDEV(hidraw_major, hidraw->minor));

- hidraw_table[hidraw->minor] = NULL;
+ drop_ref(hidraw, 1);

- if (hidraw->open) {
- hid_hw_close(hid);
- wake_up_interruptible(&hidraw->wait);
- } else {
- kfree(hidraw);
- }
mutex_unlock(&minors_lock);
}
EXPORT_SYMBOL_GPL(hidraw_disconnect);
--
-Regards
Manoj

[ 111.578116] Unable to handle kernel NULL pointer dereference at virtual address 00000001

[ 111.578134] pgd = aa870000

[ 111.578143] [00000001] *pgd=2afbb831, *pte=00000000, *ppte=00000000

[ 111.578168] Internal error: Oops: 17 [#1] PREEMPT SMP

[ 111.578352] CPU: 1 Tainted: P

[ 111.578378] PC is at rb_erase+0x1b4/0x370

[ 111.578399] LR is at __free_vmap_area+0x5c/0xf4

[ 111.578413] pc : [<801d2ba8>] lr : [<800b7fb8>] psr: 200f0013

[ 111.578419] sp : aa205d88 ip : 00000001 fp : 00000002

[ 111.578431] r10: 00000d30 r9 : 00000002 r8 : c1ab2000

[ 111.578442] r7 : 00000d30 r6 : 9ca544ec r5 : 805f38a0 r4 : 9ca24b6c

[ 111.578454] r3 : 9c8a87ec r2 : 00000001 r1 : b627bf6c r0 : 00000001

[ 111.578468] Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user

[ 111.578481] Control: 10c5387d Table: 2a87004a DAC: 00000015

[ 111.578491]

[unhandled content-type:application/octet-stream]
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