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

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Message-ID: <CAKYAXd_a=u0KKGSAe7yZy+jhtQb5Mq2ZTX=WirL7mhr3QOkTtw@mail.gmail.com>
Date: Wed, 15 Jan 2025 09:20:54 +0900
From: Namjae Jeon <linkinjeon@...nel.org>
To: Dan Carpenter <dan.carpenter@...aro.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 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.
I will apply it to #ksmbd-for-next-next.
Thanks!
>
> regards,
> dan carpenter
>
> diff --git a/fs/smb/server/transport_ipc.c b/fs/smb/server/transport_ipc.c
> index befaf42b84cc..e1e3bfff163c 100644
> --- a/fs/smb/server/transport_ipc.c
> +++ b/fs/smb/server/transport_ipc.c
> @@ -626,6 +626,9 @@ ksmbd_ipc_spnego_authen_request(const char *spnego_blob, int blob_len)
>         struct ksmbd_spnego_authen_request *req;
>         struct ksmbd_spnego_authen_response *resp;
>
> +       if (blob_len > INT_MAX)
> +               return NULL;
> +
>         msg = ipc_msg_alloc(sizeof(struct ksmbd_spnego_authen_request) +
>                         blob_len + 1);
>         if (!msg)
> @@ -805,6 +808,9 @@ struct ksmbd_rpc_command *ksmbd_rpc_write(struct ksmbd_session *sess, int handle
>         struct ksmbd_rpc_command *req;
>         struct ksmbd_rpc_command *resp;
>
> +       if (payload_sz > INT_MAX)
> +               return NULL;
> +
>         msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
>         if (!msg)
>                 return NULL;
> @@ -853,6 +859,9 @@ struct ksmbd_rpc_command *ksmbd_rpc_ioctl(struct ksmbd_session *sess, int handle
>         struct ksmbd_rpc_command *req;
>         struct ksmbd_rpc_command *resp;
>
> +       if (payload_sz > INT_MAX)
> +               return NULL;
> +
>         msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
>         if (!msg)
>                 return NULL;
> @@ -878,6 +887,9 @@ struct ksmbd_rpc_command *ksmbd_rpc_rap(struct ksmbd_session *sess, void *payloa
>         struct ksmbd_rpc_command *req;
>         struct ksmbd_rpc_command *resp;
>
> +       if (payload_sz > INT_MAX)
> +               return NULL;
> +
>         msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
>         if (!msg)
>                 return NULL;