linux-kernel - [PATCH v3 2/8] mm: userfaultfd: check for start + len overflow in validate

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Message-ID: <20230706225037.1164380-3-axelrasmussen@google.com>
Date:   Thu,  6 Jul 2023 15:50:30 -0700
From:   Axel Rasmussen <axelrasmussen@...gle.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Geffon <bgeffon@...gle.com>,
        Christian Brauner <brauner@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Gaosheng Cui <cuigaosheng1@...wei.com>,
        Huang Ying <ying.huang@...el.com>,
        Hugh Dickins <hughd@...gle.com>,
        James Houghton <jthoughton@...gle.com>,
        "Jan Alexander Steffens (heftig)" <heftig@...hlinux.org>,
        Jiaqi Yan <jiaqiyan@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "Mike Rapoport (IBM)" <rppt@...nel.org>,
        Muchun Song <muchun.song@...ux.dev>,
        Nadav Amit <namit@...are.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Peter Xu <peterx@...hat.com>,
        Ryan Roberts <ryan.roberts@....com>,
        Shuah Khan <shuah@...nel.org>,
        Suleiman Souhlal <suleiman@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        "T.J. Alumbaugh" <talumbau@...gle.com>,
        Yu Zhao <yuzhao@...gle.com>,
        ZhangPeng <zhangpeng362@...wei.com>
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org,
        Axel Rasmussen <axelrasmussen@...gle.com>
Subject: [PATCH v3 2/8] 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.

Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
---
 fs/userfaultfd.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 7cecd49e078b..2e84684c46f0 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1306,6 +1306,8 @@ 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;
 }
 
@@ -1760,14 +1762,8 @@ static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
 	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 +1923,6 @@ 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;
-- 
2.41.0.255.g8b1d071c50-goog