[PATCH v2] Cygwin: clipboard: Fix a bug in read().
Thomas Wolff
towo@towo.net
Tue Dec 7 20:18:42 GMT 2021
Am 07.12.2021 um 15:23 schrieb Corinna Vinschen:
> On Dec 7 23:00, Takashi Yano wrote:
>> - Fix a bug in fhandler_dev_clipboard::read() that the second read
>> fails with 'Bad address'.
>>
>> Addresses:
>> https://cygwin.com/pipermail/cygwin/2021-December/250141.html
>> ---
>> winsup/cygwin/fhandler_clipboard.cc | 2 +-
>> winsup/cygwin/release/3.3.4 | 6 ++++++
>> 2 files changed, 7 insertions(+), 1 deletion(-)
>> create mode 100644 winsup/cygwin/release/3.3.4
>>
>> diff --git a/winsup/cygwin/fhandler_clipboard.cc b/winsup/cygwin/fhandler_clipboard.cc
>> index 0b87dd352..ae10228a7 100644
>> --- a/winsup/cygwin/fhandler_clipboard.cc
>> +++ b/winsup/cygwin/fhandler_clipboard.cc
>> @@ -229,7 +229,7 @@ fhandler_dev_clipboard::read (void *ptr, size_t& len)
>> if (pos < (off_t) clipbuf->cb_size)
>> {
>> ret = (len > (clipbuf->cb_size - pos)) ? clipbuf->cb_size - pos : len;
>> - memcpy (ptr, &clipbuf[1] + pos , ret);
>> + memcpy (ptr, (char *) &clipbuf[1] + pos, ret);
> I'm always cringing a bit when I see this kind of expression. Personally
> I think (ptr + offset) is easier to read than &ptr[offset], but of course
> that's just me. If you agree, would it be ok to change the above to
>
> (char *) (clipbuf + 1)
>
> while you're at it? If you like the ampersand expression more, it's ok,
> too, of course. Please push.
In this specific case I think it's actually more confusing because of
the type mangling that's intended in the clipbuf.
At quick glance, it looks a bit as if the following were meant:
(char *) clipbuf + 1
I'd even make it clearer like
+ memcpy (ptr, ((char *) &clipbuf[1]) + pos, ret);
or even
+ memcpy (ptr, ((char *) (&clipbuf[1])) + pos, ret);
Thomas
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