HID: picolcd: Avoid compile warning/error triggered by copy_from_user()

With CONFIG_DEBUG_STRICT_USER_COPY_CHECKS=y compilation of PicoLCD
driver fails on copy_from_user(), without it a warning is generated:

  CC [M]  drivers/hid/hid-picolcd.o
In file included from /usr/src/linux-2.6/arch/x86/include/asm/uaccess.h:571,
                 from /usr/src/linux-2.6/arch/x86/include/asm/sections.h:5,
                 from /usr/src/linux-2.6/arch/x86/include/asm/hw_irq.h:26,
                 from /usr/src/linux-2.6/include/linux/irq.h:359,
                 from /usr/src/linux-2.6/arch/x86/include/asm/hardirq.h:5,
                 from /usr/src/linux-2.6/include/linux/hardirq.h:7,
                 from /usr/src/linux-2.6/include/linux/interrupt.h:12,
                 from /usr/src/linux-2.6/include/linux/usb.h:15,
                 from /usr/src/linux-2.6/drivers/hid/hid-picolcd.c:25:
In function 'copy_from_user',
    inlined from 'picolcd_debug_eeprom_write' at drivers/hid/hid-picolcd.c:1592:
arch/x86/include/asm/uaccess_32.h:212: error: call to 'copy_from_user_overflow' declared with attribute error: copy_from_user() buffer size is not provably correct

gcc-4.4.5 is not able to track size calculation when it is stored into
a variable, thus tell copy_from_user() maximum size via
min(*max-size*, *effective-size*) explicitly and inline how much to copy
at most.

Signed-off-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/drivers/hid/hid-picolcd.c b/drivers/hid/hid-picolcd.c
index de9cf21b3494c39d7a105f75a90078ebfe8b145e..6f0642ea1009c1aac96b0b72d651173f08d41fbc 100644 (file)
--- a/drivers/hid/hid-picolcd.c
+++ b/drivers/hid/hid-picolcd.c
@@ -1584,11 +1584,11 @@ static ssize_t picolcd_debug_eeprom_write(struct file *f, const char __user *u,
        memset(raw_data, 0, sizeof(raw_data));
        raw_data[0] = *off & 0xff;
        raw_data[1] = (*off >> 8) & 0xff;
-       raw_data[2] = s < 20 ? s : 20;
+       raw_data[2] = min((size_t)20, s);
        if (*off + raw_data[2] > 0xff)
                raw_data[2] = 0x100 - *off;
 
-       if (copy_from_user(raw_data+3, u, raw_data[2]))
+       if (copy_from_user(raw_data+3, u, min((u8)20, raw_data[2])))
                return -EFAULT;
        resp = picolcd_send_and_wait(data->hdev, REPORT_EE_WRITE, raw_data,
                        sizeof(raw_data));