HID: wacom: fix shift OOB in kfifo allocation for zero pktlen

During wacom_parse_and_register() the code calls wacom_devm_kfifo_alloc
to allocate a fifo. During this operation it passes kfifo_alloc a
fifo_size of 0. Kfifo attempts to round the size passed to it to the
next power of 2 via roundup_pow_of_two (queue-type data structures
do this to maintain efficiency of operations).

However during this phase a problem arises when the roundup_pow_of_two()
function utilises a shift exponent of fls_long(n-1), where n is the
fifo_size. Since n is 0 in this case and n is also an unsigned long,
doing n-1 causes unsigned integer wrap-around to occur making the
fifo_size 4294967295. So the code effectively does fls_long(4294967295)
which results in 64. Returning back to roundup_pow_of_two(), the code
utilises a shift exponent of 64. When a shift exponent of 64 is used
on a 64-bit type such as 1UL it results in a shift-out-of-bounds.

The root cause of the issue seems to stem from insufficient validation
of wacom_compute_pktlen(), since in this case the fifo_size comes
from wacom_wac->features.pktlen. During wacom_parse_and_register()
the wacom_compute_pktlen() function sets the pktlen as 0.

To fix this, we should handle cases where wacom_compute_pktlen()
results in 0.

Reported-by: syzbot <syzbot+d5204cbbdd921f1f7cad@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=d5204cbbdd921f1f7cad
Fixes: 5e013ad20689 ("HID: wacom: Remove static WACOM_PKGLEN_MAX limit")
Tested-by: Qasim Ijaz <qasdev00@gmail.com>
Reviewed-by: Jason Gerecke <jason.gerecke@wacom.com>
Cc: stable@vger.kernel.org
Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c
index 95a796b3e9f2a3a61d7f14bb13403d82218859c6..2d052653ba634fc8720f623ec060aacb817b3ea6 100644 (file)
--- a/drivers/hid/wacom_sys.c
+++ b/drivers/hid/wacom_sys.c
@@ -2368,6 +2368,8 @@ static int wacom_parse_and_register(struct wacom *wacom, bool wireless)
        unsigned int connect_mask = HID_CONNECT_HIDRAW;
 
        features->pktlen = wacom_compute_pktlen(hdev);
+       if (!features->pktlen)
+               return -ENODEV;
 
        if (!devres_open_group(&hdev->dev, wacom, GFP_KERNEL))
                return -ENOMEM;