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Tue, 01 Apr 2025 05:59:50 -0700 (PDT) From: Qasim Ijaz To: ping.cheng@wacom.com, jason.gerecke@wacom.com, jikos@kernel.org, bentiss@kernel.org Cc: linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot , stable@vger.kernel.org Subject: [PATCH] HID: wacom: fix shift OOB in kfifo allocation for zero pktlen Date: Tue, 1 Apr 2025 13:59:12 +0100 Message-Id: <20250401125912.73044-1-qasdev00@gmail.com> X-Mailer: git-send-email 2.39.5 Precedence: bulk X-Mailing-List: linux-input@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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 Closes: https://syzkaller.appspot.com/bug?extid=d5204cbbdd921f1f7cad Tested-by: Qasim Ijaz Cc: stable@vger.kernel.org Signed-off-by: Qasim Ijaz Reviewed-by: Jason Gerecke --- drivers/hid/wacom_sys.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c index 97393a3083ca..9b2f3dbca467 100644 --- a/drivers/hid/wacom_sys.c +++ b/drivers/hid/wacom_sys.c @@ -2361,6 +2361,8 @@ 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;