mm: userfaultfd: check for start + len overflow in validate_range

Most userfaultfd ioctls take a `start + len` range as an argument.  We
have the validate_range helper to check that such ranges are valid. 
However, some (but not all!) ioctls *also* check that `start + len`
doesn't wrap around (overflow).

Just check for this in validate_range.  This saves some repetitive code,
and adds the check to some ioctls which weren't bothering to check for it
before.

[axelrasmussen@google.com: call validate_range() on the src range too]
  Link: https://lkml.kernel.org/r/20230714182932.2608735-1-axelrasmussen@google.com
[axelrasmussen@google.com: fix src/dst validation]
  Link: https://lkml.kernel.org/r/20230810192128.1855570-1-axelrasmussen@google.com
Link: https://lkml.kernel.org/r/20230707215540.2324998-3-axelrasmussen@google.comSigned-off-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Gaosheng Cui <cuigaosheng1@huawei.com>
Cc: Huang, Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Jan Alexander Steffens (heftig) <heftig@archlinux.org>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nadav Amit <namit@vmware.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: T.J. Alumbaugh <talumbau@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: ZhangPeng <zhangpeng362@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/userfaultfd.c

@@ -1289,13 +1289,11 @@ static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
 		__wake_userfault(ctx, range);
 }
 
-static __always_inline int validate_range(struct mm_struct *mm,
-					  __u64 start, __u64 len)
+static __always_inline int validate_unaligned_range(
+	struct mm_struct *mm, __u64 start, __u64 len)
 {
 	__u64 task_size = mm->task_size;
 
-	if (start & ~PAGE_MASK)
-		return -EINVAL;
 	if (len & ~PAGE_MASK)
 		return -EINVAL;
 	if (!len)
@@ -1306,9 +1304,20 @@ static __always_inline int validate_range(struct mm_struct *mm,
 		return -EINVAL;
 	if (len > task_size - start)
 		return -EINVAL;
+	if (start + len <= start)
+		return -EINVAL;
 	return 0;
 }
 
+static __always_inline int validate_range(struct mm_struct *mm,
+					  __u64 start, __u64 len)
+{
+	if (start & ~PAGE_MASK)
+		return -EINVAL;
+
+	return validate_unaligned_range(mm, start, len);
+}
+
 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 				unsigned long arg)
 {
@@ -1757,17 +1766,15 @@ static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
 			   sizeof(uffdio_copy)-sizeof(__s64)))
 		goto out;
 
+	ret = validate_unaligned_range(ctx->mm, uffdio_copy.src,
+				       uffdio_copy.len);
+	if (ret)
+		goto out;
 	ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
 	if (ret)
 		goto out;
-	/*
-	 * double check for wraparound just in case. copy_from_user()
-	 * will later check uffdio_copy.src + uffdio_copy.len to fit
-	 * in the userland range.
-	 */
+
 	ret = -EINVAL;
-	if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
-		goto out;
 	if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
 		goto out;
 	if (uffdio_copy.mode & UFFDIO_COPY_MODE_WP)
@@ -1927,11 +1934,6 @@ static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
 		goto out;
 
 	ret = -EINVAL;
-	/* double check for wraparound just in case. */
-	if (uffdio_continue.range.start + uffdio_continue.range.len <=
-	    uffdio_continue.range.start) {
-		goto out;
-	}
 	if (uffdio_continue.mode & ~(UFFDIO_CONTINUE_MODE_DONTWAKE |
 				     UFFDIO_CONTINUE_MODE_WP))
 		goto out;