From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Biggers Subject: [PATCH] HID: uhid: prevent uhid_char_write() under KERNEL_DS Date: Wed, 14 Nov 2018 10:02:17 -0800 Message-ID: <20181114180217.195917-1-ebiggers@kernel.org> References: <20181114171447.GA87768@gmail.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20181114171447.GA87768@gmail.com> Sender: stable-owner@vger.kernel.org To: David Herrmann , Jiri Kosina , Benjamin Tissoires , linux-input@vger.kernel.org Cc: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, Dmitry Vyukov , Dmitry Torokhov , syzbot+72473edc9bf4eb1c6556@syzkaller.appspotmail.com, stable@vger.kernel.org, Jann Horn List-Id: linux-input@vger.kernel.org From: Eric Biggers When a UHID_CREATE command is written to the uhid char device, a copy_from_user() is done from a user pointer embedded in the command. When the address limit is KERNEL_DS, e.g. as is the case during sendfile(), this can read from kernel memory. Therefore, UHID_CREATE must not be allowed in this case. For consistency and to make sure all current and future uhid commands are covered, apply the restriction to uhid_char_write() as a whole rather than to UHID_CREATE specifically. Thanks to Dmitry Vyukov for adding uhid definitions to syzkaller and to Jann Horn for commit 9da3f2b740544 ("x86/fault: BUG() when uaccess helpers fault on kernel addresses"), allowing this bug to be found. Reported-by: syzbot+72473edc9bf4eb1c6556@syzkaller.appspotmail.com Fixes: d365c6cfd337 ("HID: uhid: add UHID_CREATE and UHID_DESTROY events") Cc: # v3.6+ Cc: Jann Horn Signed-off-by: Eric Biggers --- drivers/hid/uhid.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c index 3c55073136064..e94c5e248b56e 100644 --- a/drivers/hid/uhid.c +++ b/drivers/hid/uhid.c @@ -705,6 +705,12 @@ static ssize_t uhid_char_write(struct file *file, const char __user *buffer, int ret; size_t len; + if (uaccess_kernel()) { /* payload may contain a __user pointer */ + pr_err_once("%s: process %d (%s) called from kernel context, this is not allowed.\n", + __func__, task_tgid_vnr(current), current->comm); + return -EACCES; + } + /* we need at least the "type" member of uhid_event */ if (count < sizeof(__u32)) return -EINVAL; -- 2.19.1.930.g4563a0d9d0-goog