linux-kernel - Re: [PATCH RESEND] ksmbd: fix integer overflows on 32 bit systems

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Message-ID: <20f85837-68b7-404f-9284-73597feb142e@stanley.mountain>
Date: Wed, 15 Jan 2025 08:26:25 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Namjae Jeon <linkinjeon@...nel.org>
Cc: Steve French <sfrench@...ba.org>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Tom Talpey <tom@...pey.com>, linux-cifs@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH RESEND] ksmbd: fix integer overflows on 32 bit systems

On Wed, Jan 15, 2025 at 09:20:54AM +0900, Namjae Jeon wrote:
> On Tue, Jan 14, 2025 at 7:18 PM Dan Carpenter <dan.carpenter@...aro.org> wrote:
> >
> > On Tue, Jan 14, 2025 at 04:53:18PM +0900, Namjae Jeon wrote:
> > > On Mon, Jan 13, 2025 at 3:17 PM Dan Carpenter <dan.carpenter@...aro.org> wrote:
> > > >
> > > > On 32bit systems the addition operations in ipc_msg_alloc() can
> > > > potentially overflow leading to memory corruption.  Fix this using
> > > > size_add() which will ensure that the invalid allocations do not succeed.
> > > You previously said that memcpy overrun does not occur due to memory
> > > allocation failure with SIZE_MAX.
> > >
> > > Would it be better to handle integer overflows as an error before
> > > memory allocation?
> >
> > I mean we could do something like the below patch but I'd prefer to fix
> > it this way.
> >
> > > And static checkers don't detect memcpy overrun by considering memory
> > > allocation failure?
> >
> > How the struct_size()/array_size() kernel hardenning works is that if
> > you pass in a too large value instead of wrapping to a small value, the
> > math results in SIZE_MAX so the allocation will fail.  We already handle
> > allocation failures correctly so it's fine.
> >
> > The problem in this code is that on 32 bit systems if you chose a "sz"
> > value which is (unsigned int)-4 then the kvzalloc() allocation will
> > succeed but the buffer will be 4 bytes smaller than intended and the
> > "msg->sz = sz;" assignment will corrupt memory.
> >
> > Anyway, here is how the patch could look like with bounds checking instead
> > of size_add().  We could fancy it up a bit, but I don't like fancy math.
> Okay, There was a macro for max ipc payload size, So I have changed
> INT_MAX to KSMBD_IPC_MAX_PAYLOAD.

Nice.  I didn't know.  Thanks!

regards,
dan carpenter