> On 25 Jun 2015, at 14:27, Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx> wrote:
>
> On Tue, Jun 23, 2015 at 07:03:36PM +0300, Dmitry Kalinkin wrote:
>> Signed-off-by: Dmitry Kalinkin <dmitry.kalinkin@xxxxxxxxx>
>> ---
>> drivers/staging/vme/devices/vme_user.c | 47 ++++++++--------------------------
>> 1 file changed, 11 insertions(+), 36 deletions(-)
>>
> <snip>
>> @@ -178,38 +167,24 @@ static ssize_t buffer_to_user(unsigned int minor, char __user *buf,
>> size_t count, loff_t *ppos)
>> {
>> void *image_ptr;
>> - ssize_t retval;
>>
>> image_ptr = image[minor].kern_buf + *ppos;
>> + if (__copy_to_user(buf, image_ptr, (unsigned long)count))
>> + return -EFAULT;
>>
>> - retval = __copy_to_user(buf, image_ptr, (unsigned long)count);
>> - if (retval != 0) {
>> - retval = (count - retval);
>> - pr_warn("Partial copy to userspace\n");
>> - } else
>> - retval = count;
>> -
>> - /* Return number of bytes successfully read */
>> - return retval;
>> + return count;
> will it not affect the userspace code?
> previously number of bytes successfully read was returned, now incase of
> partial read -EFAULT is being returned.
Exactly.
Practically there is an access_ok() call in vfs_read() and vfs_write() that
will catch this first. I don’t know exactly what is the condition for
__copy_to_user to fail, but it is probably some rare arch-specific thing (and
we only care for x86/powerpc here). But when it happens it better be returning
proper error codes. This is why I think this is not a “we broke userspace”
situation.
Cheers,
Dmitry
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