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From:   Philipp Stanner <pstanner@redhat.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Philipp Stanner <pstanner@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Tony Luck <tony.luck@intel.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>
Cc:     linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org,
        Dave Airlie <airlied@redhat.com>
Subject: [PATCH v2] drivers/tty/vt: use standard array-copy-functions
Date:   Fri,  3 Nov 2023 12:12:08 +0100
Message-ID: <20231103111207.74621-2-pstanner@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

tty/vt currently uses memdup_user() and vmemdup_array_user() to copy
userspace arrays.

Whereas there is no danger of overflowing, the call to vmemdup_user()
currently utilizes array_size() to calculate the array size
nevertheless. This is not useful because array_size() would return
SIZE_MAX and pass it to vmemdup_user() in case of (the impossible)
overflow.

string.h from the core-API now provides the wrappers memdup_array_user()
and vmemdup_array_user() to copy userspace arrays in a standardized
manner. Additionally, they also perform generic overflow-checks.

Use these wrappers to make it more obvious and readable that arrays are
being copied.

As we are at it, remove two unnecessary empty lines.

Suggested-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Philipp Stanner <pstanner@redhat.com>
---
Changes in v2:
- Remove two empty lines from keyboard.c
- Rephrase the commit message completely to make it obvious that we're
  not actually fixing a really possible overflow here. Emphasize the
  commit being about unifying array-copying. (Al Viro)
---
 drivers/tty/vt/consolemap.c |  2 +-
 drivers/tty/vt/keyboard.c   | 10 ++++------
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/vt/consolemap.c b/drivers/tty/vt/consolemap.c
index f02d21e2a96e..313cef3322eb 100644
--- a/drivers/tty/vt/consolemap.c
+++ b/drivers/tty/vt/consolemap.c
@@ -644,7 +644,7 @@ int con_set_unimap(struct vc_data *vc, ushort ct, struct unipair __user *list)
 	if (!ct)
 		return 0;
 
-	unilist = vmemdup_user(list, array_size(sizeof(*unilist), ct));
+	unilist = vmemdup_array_user(list, ct, sizeof(*unilist));
 	if (IS_ERR(unilist))
 		return PTR_ERR(unilist);
 
diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index 1fe6107b539b..96f19ef360b5 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -1772,12 +1772,10 @@ int vt_do_diacrit(unsigned int cmd, void __user *udp, int perm)
 			return -EINVAL;
 
 		if (ct) {
-
-			dia = memdup_user(a->kbdiacr,
-					sizeof(struct kbdiacr) * ct);
+			dia = memdup_array_user(a->kbdiacr,
+						ct, sizeof(struct kbdiacr));
 			if (IS_ERR(dia))
 				return PTR_ERR(dia);
-
 		}
 
 		spin_lock_irqsave(&kbd_event_lock, flags);
@@ -1811,8 +1809,8 @@ int vt_do_diacrit(unsigned int cmd, void __user *udp, int perm)
 			return -EINVAL;
 
 		if (ct) {
-			buf = memdup_user(a->kbdiacruc,
-					  ct * sizeof(struct kbdiacruc));
+			buf = memdup_array_user(a->kbdiacruc,
+						ct, sizeof(struct kbdiacruc));
 			if (IS_ERR(buf))
 				return PTR_ERR(buf);
 		} 
-- 
2.41.0