[PATCH] ipw2x00: Replace zero-length array with flexible-array

Gustavo A. R. Silva
2020-05-07T18:50:26Z

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
int stuff;
struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
drivers/net/wireless/intel/ipw2x00/ipw2200.c | 2 -
drivers/net/wireless/intel/ipw2x00/ipw2200.h | 10 ++++-----
drivers/net/wireless/intel/ipw2x00/libipw.h | 28 +++++++++++++--------------
3 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/drivers/net/wireless/intel/ipw2x00/ipw2200.c b/drivers/net/wireless/intel/ipw2x00/ipw2200.c
index 60b5e08dd6df..64563840df00 100644
--- a/drivers/net/wireless/intel/ipw2x00/ipw2200.c
+++ b/drivers/net/wireless/intel/ipw2x00/ipw2200.c
@@ -3386,7 +3386,7 @@ struct ipw_fw {
__le32 boot_size;
__le32 ucode_size;
__le32 fw_size;
- u8 data[0];
+ u8 data[];
};

static int ipw_get_fw(struct ipw_priv *priv,
diff --git a/drivers/net/wireless/intel/ipw2x00/ipw2200.h b/drivers/net/wireless/intel/ipw2x00/ipw2200.h
index 4346520545c4..09fa7f19050f 100644
--- a/drivers/net/wireless/intel/ipw2x00/ipw2200.h
+++ b/drivers/net/wireless/intel/ipw2x00/ipw2200.h
@@ -448,7 +448,7 @@ struct tfd_command {
u8 index;
u8 length;
__le16 reserved;
- u8 payload[0];
+ u8 payload[];
} __packed;

struct tfd_data {
@@ -675,7 +675,7 @@ struct ipw_rx_frame {
// is identical)
u8 rtscts_seen; // 0x1 RTS seen ; 0x2 CTS seen
__le16 length;
- u8 data[0];
+ u8 data[];
} __packed;

struct ipw_rx_header {
@@ -1002,7 +1002,7 @@ struct ipw_cmd { /* XXX */
* Incoming parameters listed 1-st, followed by outcoming params.
* nParams=(len+3)/4+status_len
*/
- u32 param[0];
+ u32 param[];
} __packed;

#define STATUS_HCMD_ACTIVE (1<<0) /**< host command in progress */
@@ -1108,7 +1108,7 @@ struct ipw_fw_error { /* XXX */
u32 log_len;
struct ipw_error_elem *elem;
struct ipw_event *log;
- u8 payload[0];
+ u8 payload[];
} __packed;

#ifdef CONFIG_IPW2200_PROMISCUOUS
@@ -1153,7 +1153,7 @@ struct ipw_rt_hdr {
s8 rt_dbmsignal; /* signal in dbM, kluged to signed */
s8 rt_dbmnoise;
u8 rt_antenna; /* antenna number */
- u8 payload[0]; /* payload... */
+ u8 payload[]; /* payload... */
} __packed;
#endif

diff --git a/drivers/net/wireless/intel/ipw2x00/libipw.h b/drivers/net/wireless/intel/ipw2x00/libipw.h
index e4a6ab4e8391..e87538a8b88b 100644
--- a/drivers/net/wireless/intel/ipw2x00/libipw.h
+++ b/drivers/net/wireless/intel/ipw2x00/libipw.h
@@ -334,7 +334,7 @@ struct libipw_hdr_1addr {
__le16 frame_ctl;
__le16 duration_id;
u8 addr1[ETH_ALEN];
- u8 payload[0];
+ u8 payload[];
} __packed;

struct libipw_hdr_2addr {
@@ -342,7 +342,7 @@ struct libipw_hdr_2addr {
__le16 duration_id;
u8 addr1[ETH_ALEN];
u8 addr2[ETH_ALEN];
- u8 payload[0];
+ u8 payload[];
} __packed;

struct libipw_hdr_3addr {
@@ -352,7 +352,7 @@ struct libipw_hdr_3addr {
u8 addr2[ETH_ALEN];
u8 addr3[ETH_ALEN];
__le16 seq_ctl;
- u8 payload[0];
+ u8 payload[];
} __packed;

struct libipw_hdr_4addr {
@@ -363,7 +363,7 @@ struct libipw_hdr_4addr {
u8 addr3[ETH_ALEN];
__le16 seq_ctl;
u8 addr4[ETH_ALEN];
- u8 payload[0];
+ u8 payload[];
} __packed;

struct libipw_hdr_3addrqos {
@@ -380,7 +380,7 @@ struct libipw_hdr_3addrqos {
struct libipw_info_element {
u8 id;
u8 len;
- u8 data[0];
+ u8 data[];
} __packed;

/*
@@ -406,7 +406,7 @@ struct libipw_auth {
__le16 transaction;
__le16 status;
/* challenge */
- struct libipw_info_element info_element[0];
+ struct libipw_info_element info_element[];
} __packed;

struct libipw_channel_switch {
@@ -442,7 +442,7 @@ struct libipw_disassoc {
struct libipw_probe_request {
struct libipw_hdr_3addr header;
/* SSID, supported rates */
- struct libipw_info_element info_element[0];
+ struct libipw_info_element info_element[];
} __packed;

struct libipw_probe_response {
@@ -452,7 +452,7 @@ struct libipw_probe_response {
__le16 capability;
/* SSID, supported rates, FH params, DS params,
* CF params, IBSS params, TIM (if beacon), RSN */
- struct libipw_info_element info_element[0];
+ struct libipw_info_element info_element[];
} __packed;

/* Alias beacon for probe_response */
@@ -463,7 +463,7 @@ struct libipw_assoc_request {
__le16 capability;
__le16 listen_interval;
/* SSID, supported rates, RSN */
- struct libipw_info_element info_element[0];
+ struct libipw_info_element info_element[];
} __packed;

struct libipw_reassoc_request {
@@ -471,7 +471,7 @@ struct libipw_reassoc_request {
__le16 capability;
__le16 listen_interval;
u8 current_ap[ETH_ALEN];
- struct libipw_info_element info_element[0];
+ struct libipw_info_element info_element[];
} __packed;

struct libipw_assoc_response {
@@ -480,7 +480,7 @@ struct libipw_assoc_response {
__le16 status;
__le16 aid;
/* supported rates */
- struct libipw_info_element info_element[0];
+ struct libipw_info_element info_element[];
} __packed;

struct libipw_txb {
@@ -490,7 +490,7 @@ struct libipw_txb {
u8 reserved;
u16 frag_size;
u16 payload_size;
- struct sk_buff *fragments[0];
+ struct sk_buff *fragments[];
};

/* SWEEP TABLE ENTRIES NUMBER */
@@ -594,7 +594,7 @@ struct libipw_ibss_dfs {
struct libipw_info_element ie;
u8 owner[ETH_ALEN];
u8 recovery_interval;
- struct libipw_channel_map channel_map[0];
+ struct libipw_channel_map channel_map[];
};

struct libipw_csa {
@@ -830,7 +830,7 @@ struct libipw_device {

/* This must be the last item so that it points to the data
* allocated beyond this structure by alloc_libipw */
- u8 priv[0];
+ u8 priv[];
};

#define IEEE_A (1<<0)