USB: sisusbvga: Fix a potential UB casued by left shifting a negative value

[ Upstream commit 2b53a19284f537168fb506f2f40d7fda40a01162 ]

The char buffer buf, receives data directly from user space,
so its content might be negative and its elements are left
shifted to form an unsigned integer.

Since left shifting a negative value is undefined behavior, thus
change the char to u8 to elimintate this UB.

Signed-off-by: Changming Liu <charley.ashbringer@gmail.com>
Link: https://lore.kernel.org/r/20200711043018.928-1-charley.ashbringer@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/usb/misc/sisusbvga/sisusb.c b/drivers/usb/misc/sisusbvga/sisusb.c
index 895e8c0..30b3bdc 100644 (file)
--- a/drivers/usb/misc/sisusbvga/sisusb.c
+++ b/drivers/usb/misc/sisusbvga/sisusb.c
@@ -762,7 +762,7 @@ static int sisusb_write_mem_bulk(struct sisusb_usb_data *sisusb, u32 addr,
        u8   swap8, fromkern = kernbuffer ? 1 : 0;
        u16  swap16;
        u32  swap32, flag = (length >> 28) & 1;
-       char buf[4];
+       u8 buf[4];
 
        /* if neither kernbuffer not userbuffer are given, assume
         * data in obuf