clone3: switch to copy_struct_from_user()

Switch clone3() syscall from it's own copying struct clone_args from
userspace to the new dedicated copy_struct_from_user() helper.

The change is very straightforward, and helps unify the syscall
interface for struct-from-userspace syscalls. Additionally, explicitly
define CLONE_ARGS_SIZE_VER0 to match the other users of the
struct-extension pattern.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
[christian.brauner@ubuntu.com: improve commit message]
Link: https://lore.kernel.org/r/20191001011055.19283-3-cyphar@cyphar.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

1 files changed, 7 insertions, 27 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index f9572f416126..2ef529869c64 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2525,39 +2525,19 @@ SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
 #ifdef __ARCH_WANT_SYS_CLONE3
 noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
                                               struct clone_args __user *uargs,
-                                              size_t size)
+                                              size_t usize)
 {
+        int err;
         struct clone_args args;
 
-        if (unlikely(size > PAGE_SIZE))
+        if (unlikely(usize > PAGE_SIZE))
                 return -E2BIG;
-
-        if (unlikely(size < sizeof(struct clone_args)))
+        if (unlikely(usize < CLONE_ARGS_SIZE_VER0))
                 return -EINVAL;
 
-        if (unlikely(!access_ok(uargs, size)))
-                return -EFAULT;
-
-        if (size > sizeof(struct clone_args)) {
-                unsigned char __user *addr;
-                unsigned char __user *end;
-                unsigned char val;
-
-                addr = (void __user *)uargs + sizeof(struct clone_args);
-                end = (void __user *)uargs + size;
-
-                for (; addr < end; addr++) {
-                        if (get_user(val, addr))
-                                return -EFAULT;
-                        if (val)
-                                return -E2BIG;
-                }
-
-                size = sizeof(struct clone_args);
-        }
-
-        if (copy_from_user(&args, uargs, size))
-                return -EFAULT;
+        err = copy_struct_from_user(&args, sizeof(args), uargs, usize);
+        if (err)
+                return err;
 
         /*
          * Verify that higher 32bits of exit_signal are unset and that