4.4-stable review patch. If anyone has any objections, please let me know.
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From: Eric Biggers ebiggers@google.com
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 | 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: