linux-kernel - [PATCH] usb: functionfs: avoid memcpy() field overflow warning

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Message-Id: <20230703123053.3117488-1-arnd@kernel.org>
Date:   Mon,  3 Jul 2023 14:30:32 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Udipto Goswami <quic_ugoswami@...cinc.com>,
        John Keeping <john@...ping.me.uk>,
        Linyu Yuan <quic_linyyuan@...cinc.com>,
        Dan Carpenter <error27@...il.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] usb: functionfs: avoid memcpy() field overflow warning

From: Arnd Bergmann <arnd@...db.de>

__ffs_func_bind_do_os_desc() copies both the CompatibleID and SubCompatibleID
fields of the usb_ext_compat_desc structure into an array, which triggers
a warning in the fortified memcpy():

In file included from drivers/usb/gadget/function/f_fs.c:17:
In file included from include/linux/string.h:254:
include/linux/fortify-string.h:592:4: error: call to '__read_overflow2_field' declared with 'warning' attribute: detected read beyond size of field (2nd parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
                        __read_overflow2_field(q_size_field, size);

Usually we can avoid this by using a struct_group() inside of the structure
definition, but this might cause problems in userspace since it is in a uapi
header.

Just copy the two members individually.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/usb/gadget/function/f_fs.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index f41a385a5c421..b8f9e52e6db6b 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -2933,8 +2933,9 @@ static int __ffs_func_bind_do_os_desc(enum ffs_os_desc_type type,
 		t = &func->function.os_desc_table[desc->bFirstInterfaceNumber];
 		t->if_id = func->interfaces_nums[desc->bFirstInterfaceNumber];
 		memcpy(t->os_desc->ext_compat_id, &desc->CompatibleID,
-		       ARRAY_SIZE(desc->CompatibleID) +
-		       ARRAY_SIZE(desc->SubCompatibleID));
+		       sizeof(desc->CompatibleID));
+		memcpy(t->os_desc->ext_compat_id + sizeof(desc->CompatibleID),
+			&desc->SubCompatibleID, sizeof(desc->SubCompatibleID));
 		length = sizeof(*desc);
 	}
 		break;
-- 
2.39.2