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Message-ID: <CABBYNZ+N5UM3pvTiMSNx-EhhTOOXwEziO7BQoYK+u8=TtSQEnw@mail.gmail.com>
Date: Tue, 26 Mar 2024 17:12:31 -0400
From: Luiz Augusto von Dentz <luiz.dentz@...il.com>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Marcel Holtmann <marcel@...tmann.org>, Johan Hedberg <johan.hedberg@...il.com>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, linux-bluetooth@...r.kernel.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] Bluetooth: L2CAP: Avoid -Wflex-array-member-not-at-end
warnings
Hi Gustavo,
On Tue, Mar 26, 2024 at 4:02 PM Gustavo A. R. Silva
<gustavoars@...nel.org> wrote:
>
> -Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
> ready to enable it globally.
>
> There are currently a couple of objects (`req` and `rsp`), in a couple
> of structures, that contain flexible structures (`struct l2cap_ecred_conn_req`
> and `struct l2cap_ecred_conn_rsp`), for example:
>
> struct l2cap_ecred_rsp_data {
> struct {
> struct l2cap_ecred_conn_rsp rsp;
> __le16 scid[L2CAP_ECRED_MAX_CID];
> } __packed pdu;
> int count;
> };
>
> in the struct above, `struct l2cap_ecred_conn_rsp` is a flexible
> structure:
>
> struct l2cap_ecred_conn_rsp {
> __le16 mtu;
> __le16 mps;
> __le16 credits;
> __le16 result;
> __le16 dcid[];
> };
>
> So, in order to avoid ending up with a flexible-array member in the
> middle of another structure, we use the `struct_group_tagged()` (and
> `__struct_group()` when the flexible structure is `__packed`) helper
> to separate the flexible array from the rest of the members in the
> flexible structure:
>
> struct l2cap_ecred_conn_rsp {
> struct_group_tagged(l2cap_ecred_conn_rsp_hdr, hdr,
>
> ... the rest of members
>
> );
> __le16 dcid[];
> };
Wouldn't it be better, more readable at least, to not define the
l2cap_ecred_conn_rsp_hdr inside thought? Instead just do:
struct_group_tagged(l2cap_ecred_conn_rsp_hdr, hdr,
...
};
struct l2cap_ecred_conn_rsp {
struct l2cap_ecred_conn_rsp_hdr hdr;
__le16 dcid[];
};
Or was this done this way in order to maintain the same fields?
> With the change described above, we now declare objects of the type of
> the tagged struct, in this example `struct l2cap_ecred_conn_rsp_hdr`,
> without embedding flexible arrays in the middle of other structures:
>
> struct l2cap_ecred_rsp_data {
> struct {
> struct l2cap_ecred_conn_rsp_hdr rsp;
> __le16 scid[L2CAP_ECRED_MAX_CID];
> } __packed pdu;
> int count;
> };
>
> Also, when the flexible-array member needs to be accessed, we use
> `container_of()` to retrieve a pointer to the flexible structure.
>
> We also use the `DEFINE_RAW_FLEX()` helper for a couple of on-stack
> definitions of a flexible structure where the size of the flexible-array
> member is known at compile-time.
>
> So, with these changes, fix the following warnings:
> net/bluetooth/l2cap_core.c:1260:45: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> net/bluetooth/l2cap_core.c:3740:45: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> net/bluetooth/l2cap_core.c:4999:45: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> net/bluetooth/l2cap_core.c:7116:47: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
>
> Link: https://github.com/KSPP/linux/issues/202
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>
> Hi!
>
> I wonder if `struct l2cap_ecred_conn_rsp` should also be `__packed`.
>
> Thanks
> - Gustavo
>
> include/net/bluetooth/l2cap.h | 20 +++++++++------
> net/bluetooth/l2cap_core.c | 46 ++++++++++++++++-------------------
> 2 files changed, 33 insertions(+), 33 deletions(-)
>
> diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
> index a4278aa618ab..92a143517d83 100644
> --- a/include/net/bluetooth/l2cap.h
> +++ b/include/net/bluetooth/l2cap.h
> @@ -463,18 +463,22 @@ struct l2cap_le_credits {
> #define L2CAP_ECRED_MAX_CID 5
>
> struct l2cap_ecred_conn_req {
> - __le16 psm;
> - __le16 mtu;
> - __le16 mps;
> - __le16 credits;
> + __struct_group(l2cap_ecred_conn_req_hdr, hdr, __packed,
> + __le16 psm;
> + __le16 mtu;
> + __le16 mps;
> + __le16 credits;
> + );
> __le16 scid[];
> } __packed;
>
> struct l2cap_ecred_conn_rsp {
> - __le16 mtu;
> - __le16 mps;
> - __le16 credits;
> - __le16 result;
> + struct_group_tagged(l2cap_ecred_conn_rsp_hdr, hdr,
> + __le16 mtu;
> + __le16 mps;
> + __le16 credits;
> + __le16 result;
> + );
> __le16 dcid[];
> };
>
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 467b242d8be0..bf087eca489e 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -1257,7 +1257,7 @@ static void l2cap_le_connect(struct l2cap_chan *chan)
>
> struct l2cap_ecred_conn_data {
> struct {
> - struct l2cap_ecred_conn_req req;
> + struct l2cap_ecred_conn_req_hdr req;
> __le16 scid[5];
> } __packed pdu;
Can't we just use DEFINE_RAW_FLEX for the pdu field above?
> struct l2cap_chan *chan;
> @@ -3737,7 +3737,7 @@ static void l2cap_ecred_list_defer(struct l2cap_chan *chan, void *data)
>
> struct l2cap_ecred_rsp_data {
> struct {
> - struct l2cap_ecred_conn_rsp rsp;
> + struct l2cap_ecred_conn_rsp_hdr rsp;
> __le16 scid[L2CAP_ECRED_MAX_CID];
> } __packed pdu;
Ditto.
> int count;
> @@ -3746,6 +3746,8 @@ struct l2cap_ecred_rsp_data {
> static void l2cap_ecred_rsp_defer(struct l2cap_chan *chan, void *data)
> {
> struct l2cap_ecred_rsp_data *rsp = data;
> + struct l2cap_ecred_conn_rsp *rsp_flex =
> + container_of(&rsp->pdu.rsp, struct l2cap_ecred_conn_rsp, hdr);
>
> if (test_bit(FLAG_ECRED_CONN_REQ_SENT, &chan->flags))
> return;
> @@ -3755,7 +3757,7 @@ static void l2cap_ecred_rsp_defer(struct l2cap_chan *chan, void *data)
>
> /* Include all channels pending with the same ident */
> if (!rsp->pdu.rsp.result)
> - rsp->pdu.rsp.dcid[rsp->count++] = cpu_to_le16(chan->scid);
> + rsp_flex->dcid[rsp->count++] = cpu_to_le16(chan->scid);
> else
> l2cap_chan_del(chan, ECONNRESET);
> }
> @@ -4995,10 +4997,7 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
> u8 *data)
> {
> struct l2cap_ecred_conn_req *req = (void *) data;
> - struct {
> - struct l2cap_ecred_conn_rsp rsp;
> - __le16 dcid[L2CAP_ECRED_MAX_CID];
> - } __packed pdu;
> + DEFINE_RAW_FLEX(struct l2cap_ecred_conn_rsp, pdu, dcid, L2CAP_ECRED_MAX_CID);
> struct l2cap_chan *chan, *pchan;
> u16 mtu, mps;
> __le16 psm;
> @@ -5017,7 +5016,7 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
> cmd_len -= sizeof(*req);
> num_scid = cmd_len / sizeof(u16);
>
> - if (num_scid > ARRAY_SIZE(pdu.dcid)) {
> + if (num_scid > L2CAP_ECRED_MAX_CID) {
> result = L2CAP_CR_LE_INVALID_PARAMS;
> goto response;
> }
> @@ -5046,7 +5045,7 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
>
> BT_DBG("psm 0x%2.2x mtu %u mps %u", __le16_to_cpu(psm), mtu, mps);
>
> - memset(&pdu, 0, sizeof(pdu));
> + memset(pdu, 0, sizeof(*pdu));
>
> /* Check if we have socket listening on psm */
> pchan = l2cap_global_chan_by_psm(BT_LISTEN, psm, &conn->hcon->src,
> @@ -5072,8 +5071,8 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
>
> BT_DBG("scid[%d] 0x%4.4x", i, scid);
>
> - pdu.dcid[i] = 0x0000;
> - len += sizeof(*pdu.dcid);
> + pdu->dcid[i] = 0x0000;
> + len += sizeof(*pdu->dcid);
>
> /* Check for valid dynamic CID range */
> if (scid < L2CAP_CID_DYN_START || scid > L2CAP_CID_LE_DYN_END) {
> @@ -5107,13 +5106,13 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
> l2cap_ecred_init(chan, __le16_to_cpu(req->credits));
>
> /* Init response */
> - if (!pdu.rsp.credits) {
> - pdu.rsp.mtu = cpu_to_le16(chan->imtu);
> - pdu.rsp.mps = cpu_to_le16(chan->mps);
> - pdu.rsp.credits = cpu_to_le16(chan->rx_credits);
> + if (!pdu->credits) {
> + pdu->mtu = cpu_to_le16(chan->imtu);
> + pdu->mps = cpu_to_le16(chan->mps);
> + pdu->credits = cpu_to_le16(chan->rx_credits);
> }
>
> - pdu.dcid[i] = cpu_to_le16(chan->scid);
> + pdu->dcid[i] = cpu_to_le16(chan->scid);
>
> __set_chan_timer(chan, chan->ops->get_sndtimeo(chan));
>
> @@ -5135,13 +5134,13 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
> l2cap_chan_put(pchan);
>
> response:
> - pdu.rsp.result = cpu_to_le16(result);
> + pdu->result = cpu_to_le16(result);
>
> if (defer)
> return 0;
>
> l2cap_send_cmd(conn, cmd->ident, L2CAP_ECRED_CONN_RSP,
> - sizeof(pdu.rsp) + len, &pdu);
> + sizeof(*pdu) + len, pdu);
>
> return 0;
> }
> @@ -7112,14 +7111,11 @@ EXPORT_SYMBOL_GPL(l2cap_chan_connect);
> static void l2cap_ecred_reconfigure(struct l2cap_chan *chan)
> {
> struct l2cap_conn *conn = chan->conn;
> - struct {
> - struct l2cap_ecred_reconf_req req;
> - __le16 scid;
> - } pdu;
> + DEFINE_RAW_FLEX(struct l2cap_ecred_reconf_req, pdu, scid, 1);
>
> - pdu.req.mtu = cpu_to_le16(chan->imtu);
> - pdu.req.mps = cpu_to_le16(chan->mps);
> - pdu.scid = cpu_to_le16(chan->scid);
> + pdu->mtu = cpu_to_le16(chan->imtu);
> + pdu->mps = cpu_to_le16(chan->mps);
> + pdu->scid[0] = cpu_to_le16(chan->scid);
>
> chan->ident = l2cap_get_ident(conn);
>
> --
> 2.34.1
>
--
Luiz Augusto von Dentz
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