From: Al Viro <viro@zeniv.linux.org.uk>
To: Jhih Ming Huang <fbihjmeric@gmail.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
fabioaiuto83@gmail.com, ross.schm.dev@gmail.com,
maqianga@uniontech.com, marcocesati@gmail.com,
linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] rtw_security: fix cast to restricted __le32
Date: Mon, 14 Jun 2021 17:03:40 +0000 [thread overview]
Message-ID: <YMeL7PjstV601pbN@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <CAKgboZ9P2afm7-eOE3COrKVDkFZ_g288KfJAyQiwzC6fN75VmA@mail.gmail.com>
On Mon, Jun 14, 2021 at 11:27:03PM +0800, Jhih Ming Huang wrote:
> Thanks for your explanation.
>
> To clarify, even though it might be false positives in some senses,
> following "hold the variable native-endian and check the conversion
> done correctly"
> is much easier than the other way. And it's exactly the current implementation.
>
> So it's better to keep the current implementation and ignore the
> warnings, right?
Umm... If that's the case, the warnings should go away if you use
cpu_to_le32() for conversions from native to l-e and le32_to_cpu()
for conversions from l-e to native.
IOW, the choice between those should annotate what's going on.
In your case doing
*((u32 *)crc) = le32_to_cpu((__force __le32)~crc32_le(~0, payload, length - 4));
is wrong - you have
crc32_le(...) native-endian
~crc32_le(...) - ditto
le32_to_cpu(~crc32_le(...)) - byteswapped native-endian on b-e, unchanged on
l-e. So result will be little-endian representation of ~crc32(...) in all
cases. IOW, it's cpu_to_le32(~crc32_le(...)), misannotated as native-endian
instead of little-endian it actually is.
Then you store that value (actually __le32) into *(u32 *)crc. Seeing that
crc is u8[4] there, that *(u32 *) is misleading - you are actually storing
__le32 there (and, AFAICS, doing noting with the result). The same story
in rtw_tkip_decrypt(), only there you do use the result later.
So just make it __le32 crc and
crc = cpu_to_le32(~crc32_le(~0, payload, length - 4));
with
if (crc[3] != payload[length - 1] || crc[2] != payload[length - 2] ||
crc[1] != payload[length - 3] || crc[0] != payload[length - 4])
turned into
if (memcmp(&crc, payload + length - 4, 4) != 0)
(or (crc != get_unaligned((__le32 *)(payload + length - 4))),
for that matter, to document what's going on and let the damn thing
pick the optimal implementation for given architecture).
Incidentally, your secmicgetuint32() is simply get_unaligned_le32()
and secmicputuint32() - put_unaligned_le32(). No need to reinvent
that wheel...
next prev parent reply other threads:[~2021-06-14 17:03 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-13 12:28 [PATCH v2] rtw_security: fix cast to restricted __le32 Jhih-Ming Huang
2021-06-13 12:34 ` Greg KH
2021-06-13 16:40 ` Jhih Ming Huang
2021-06-14 14:14 ` Al Viro
2021-06-14 15:27 ` Jhih Ming Huang
2021-06-14 17:03 ` Al Viro [this message]
2021-06-18 18:17 ` [PATCH v3] " Jhih-Ming Huang
2021-06-18 19:29 ` Al Viro
2021-06-19 7:52 ` [PATCH v4] " Jhih-Ming Huang
2021-06-21 8:19 ` [PATCH v5] " Jhih-Ming Huang
2021-06-21 15:48 ` [PATCH v6] " Jhih-Ming Huang
2021-06-21 15:51 ` [PATCH v5] " Jhih-Ming Huang
2021-06-22 9:31 ` David Laight
2021-07-04 10:31 ` [PATCH v7] " Jhih-Ming Huang
2021-07-04 19:05 ` Greg KH
2021-08-01 15:51 ` Jhih-Ming Huang
2021-08-05 11:17 ` Greg KH
2021-06-19 9:20 ` [PATCH v3] " Jhih-Ming Huang
2021-06-18 18:28 ` [PATCH v2] " Jhih Ming Huang
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