4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Biggers <ebiggers@xxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: d365c6cfd337 ("HID: uhid: add UHID_CREATE and UHID_DESTROY events")
Cc: <stable@xxxxxxxxxxxxxxx> # v3.6+
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Reviewed-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/hid/uhid.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -12,6 +12,7 @@
#include <linux/atomic.h>
#include <linux/compat.h>
+#include <linux/cred.h>
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/hid.h>
@@ -24,6 +25,7 @@
#include <linux/spinlock.h>
#include <linux/uhid.h>
#include <linux/wait.h>
+#include <linux/uaccess.h>
#define UHID_NAME "uhid"
#define UHID_BUFSIZE 32
@@ -721,6 +723,17 @@ static ssize_t uhid_char_write(struct fi
switch (uhid->input_buf.type) {
case UHID_CREATE:
+ /*
+ * 'struct uhid_create_req' contains a __user pointer which is
+ * copied from, so it's unsafe to allow this with elevated
+ * privileges (e.g. from a setuid binary) or via kernel_write().
+ */
+ if (file->f_cred != current_cred() || uaccess_kernel()) {
+ pr_err_once("UHID_CREATE from different security context by process %d (%s), this is not allowed.\n",
+ task_tgid_vnr(current), current->comm);
+ ret = -EACCES;
+ goto unlock;
+ }
ret = uhid_dev_create(uhid, &uhid->input_buf);
break;
case UHID_CREATE2:
