[PATCH 2/2] HID: hidraw, fix a NULL pointer dereference in hidraw_write

[Antonio Ospite <ospite@xxxxxxxxxxxxxxxxx>]

BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
IP: [<ffffffffa0f0a625>] hidraw_write+0x3b/0x116 [hid]
[...]

This is reproducible by disconnecting the device while userspace writes
to dev node in a loop and doesn't check return values in order to exit
the loop, like in the following test program:

int main(int argc, char *argv[])
{
	int fd = -1;
	unsigned char report[2] = {0x01, 0x00};
	int ret;

	if (argc != 2) {
		fprintf(stderr, "usage: %s </dev/hidrawX>\n", argv[0]);
		exit(1);
	}

	fd = open(argv[1], O_RDWR);
	if (fd < 0) {
		perror("hidraw open");
		exit(1);
	}

	while (1) {
		ret = write(fd, report, sizeof(report));
		printf("ret: %d\n", ret);
	}

	close(fd);
	exit(0);
}

Signed-off-by: Antonio Ospite <ospite@xxxxxxxxxxxxxxxxx>
---
 drivers/hid/hidraw.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/hid/hidraw.c b/drivers/hid/hidraw.c
index 9eaf6ae..a3866b5 100644
--- a/drivers/hid/hidraw.c
+++ b/drivers/hid/hidraw.c
@@ -109,6 +109,12 @@ static ssize_t hidraw_write(struct file *file, const char __user *buffer, size_t
 	int ret = 0;
 
 	mutex_lock(&minors_lock);
+
+	if (!hidraw_table[minor]) {
+		ret = -ENODEV;
+		goto out;
+	}
+
 	dev = hidraw_table[minor]->hid;
 
 	if (!dev->hid_output_raw_report) {
-- 
1.7.1

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