HID: uhid: forbid UHID_CREATE under KERNEL_DS or elevated privileges
authorEric Biggers <ebiggers@google.com>
Wed, 14 Nov 2018 21:55:09 +0000 (13:55 -0800)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Tue, 27 Nov 2018 15:10:51 +0000 (16:10 +0100)
commit540f89376ba2949f53ed6f057fea321be848cd43
tree31a2b0e083392d0ac5bd8cc4925c5c2fa95f932f
parent3cf1a2b4e0b3eae21abd25d535142e7b6ac3209c
HID: uhid: forbid UHID_CREATE under KERNEL_DS or elevated privileges

commit 8c01db7619f07c85c5cd81ec5eb83608b56c88f5 upstream.

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
sys_sendfile(), this can read from kernel memory.  Alternatively,
information can be leaked from a setuid binary that is tricked to write
to the file descriptor.  Therefore, forbid UHID_CREATE in these cases.

No other commands in uhid_char_write() are affected by this bug and
UHID_CREATE is marked as "obsolete", so apply the restriction to
UHID_CREATE only rather than to uhid_char_write() entirely.

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: <stable@vger.kernel.org> # v3.6+
Cc: Jann Horn <jannh@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Jann Horn <jannh@google.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/hid/uhid.c