splice: missing user pointer access verification

vmsplice_to_user() must always check the user pointer and length
with access_ok() before copying. Likewise, for the slow path of
copy_from_user_mmap_sem() we need to check that we may read from
the user region.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Cc: Wojciech Purczynski <cliph@research.coseinc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/splice.c

@@ -1179,6 +1179,9 @@ static int copy_from_user_mmap_sem(void *dst, const void __user *src, size_t n)
 {
 	int partial;
 
+	if (!access_ok(VERIFY_READ, src, n))
+		return -EFAULT;
+
 	pagefault_disable();
 	partial = __copy_from_user_inatomic(dst, src, n);
 	pagefault_enable();
@@ -1387,6 +1390,11 @@ static long vmsplice_to_user(struct file *file, const struct iovec __user *iov,
 			break;
 		}
 
+		if (unlikely(!access_ok(VERIFY_WRITE, base, len))) {
+			error = -EFAULT;
+			break;
+		}
+
 		sd.len = 0;
 		sd.total_len = len;
 		sd.flags = flags;