iwlwifi: Replace zero-length array with flexible-array

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>
Link: https://lore.kernel.org/r/20200507185538.GA14674@embeddedor
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

diff --git a/drivers/net/wireless/intel/iwlwifi/dvm/commands.h b/drivers/net/wireless/intel/iwlwifi/dvm/commands.h
index 0f4be4b..fdcc129 100644 (file)
--- a/drivers/net/wireless/intel/iwlwifi/dvm/commands.h
+++ b/drivers/net/wireless/intel/iwlwifi/dvm/commands.h
@@ -1023,7 +1023,7 @@ struct iwl_wep_cmd {
        u8 global_key_type;
        u8 flags;
        u8 reserved;
-       struct iwl_wep_key key[0];
+       struct iwl_wep_key key[];
 } __packed;
 
 #define WEP_KEY_WEP_TYPE 1
@@ -1305,7 +1305,7 @@ struct iwl_tx_cmd {
         * length is 26 or 30 bytes, followed by payload data
         */
        u8 payload[0];
-       struct ieee80211_hdr hdr[0];
+       struct ieee80211_hdr hdr[];
 } __packed;
 
 /*
@@ -2380,7 +2380,7 @@ struct iwl_scan_cmd {
         * for one scan to complete (i.e. receive SCAN_COMPLETE_NOTIFICATION)
         * before requesting another scan.
         */
-       u8 data[0];
+       u8 data[];
 } __packed;
 
 /* Can abort will notify by complete notification with abort status. */
@@ -2475,7 +2475,7 @@ struct iwl_tx_beacon_cmd {
        __le16 tim_idx;
        u8 tim_size;
        u8 reserved1;
-       struct ieee80211_hdr frame[0];  /* beacon frame */
+       struct ieee80211_hdr frame[];   /* beacon frame */
 } __packed;
 
 /******************************************************************************
@@ -3188,7 +3188,7 @@ struct iwl_calib_hdr {
 
 struct iwl_calib_cmd {
        struct iwl_calib_hdr hdr;
-       u8 data[0];
+       u8 data[];
 } __packed;
 
 struct iwl_calib_xtal_freq_cmd {
@@ -3216,7 +3216,7 @@ struct iwl_calib_temperature_offset_v2_cmd {
 /* IWL_PHY_CALIBRATE_CHAIN_NOISE_RESET_CMD */
 struct iwl_calib_chain_noise_reset_cmd {
        struct iwl_calib_hdr hdr;
-       u8 data[0];
+       u8 data[];
 };
 
 /* IWL_PHY_CALIBRATE_CHAIN_NOISE_GAIN_CMD */

diff --git a/drivers/net/wireless/intel/iwlwifi/fw/api/nvm-reg.h b/drivers/net/wireless/intel/iwlwifi/fw/api/nvm-reg.h
index fd719c3..b6c31f0 100644 (file)
--- a/drivers/net/wireless/intel/iwlwifi/fw/api/nvm-reg.h
+++ b/drivers/net/wireless/intel/iwlwifi/fw/api/nvm-reg.h
@@ -361,7 +361,7 @@ struct iwl_mcc_update_resp_v3 {
        __le16 time;
        __le16 geo_info;
        __le32 n_channels;
-       __le32 channels[0];
+       __le32 channels[];
 } __packed; /* LAR_UPDATE_MCC_CMD_RESP_S_VER_3 */
 
 /**
@@ -390,7 +390,7 @@ struct iwl_mcc_update_resp {
        u8 source_id;
        u8 reserved[3];
        __le32 n_channels;
-       __le32 channels[0];
+       __le32 channels[];
 } __packed; /* LAR_UPDATE_MCC_CMD_RESP_S_VER_4 */
 
 /**

diff --git a/drivers/net/wireless/intel/iwlwifi/fw/debugfs.c b/drivers/net/wireless/intel/iwlwifi/fw/debugfs.c
index 6e72c27..267ad4e 100644 (file)
--- a/drivers/net/wireless/intel/iwlwifi/fw/debugfs.c
+++ b/drivers/net/wireless/intel/iwlwifi/fw/debugfs.c
@@ -260,7 +260,7 @@ struct hcmd_write_data {
        __be32 cmd_id;
        __be32 flags;
        __be16 length;
-       u8 data[0];
+       u8 data[];
 } __packed;
 
 static ssize_t iwl_dbgfs_send_hcmd_write(struct iwl_fw_runtime *fwrt, char *buf,

diff --git a/drivers/net/wireless/intel/iwlwifi/iwl-op-mode.h b/drivers/net/wireless/intel/iwlwifi/iwl-op-mode.h
index 3008a52..b35b892 100644 (file)
--- a/drivers/net/wireless/intel/iwlwifi/iwl-op-mode.h
+++ b/drivers/net/wireless/intel/iwlwifi/iwl-op-mode.h
@@ -175,7 +175,7 @@ void iwl_opmode_deregister(const char *name);
 struct iwl_op_mode {
        const struct iwl_op_mode_ops *ops;
 
-       char op_mode_specific[0] __aligned(sizeof(void *));
+       char op_mode_specific[] __aligned(sizeof(void *));
 };
 
 static inline void iwl_op_mode_stop(struct iwl_op_mode *op_mode)

diff --git a/drivers/net/wireless/intel/iwlwifi/iwl-trans.h b/drivers/net/wireless/intel/iwlwifi/iwl-trans.h
index a301e24..34788e7 100644 (file)
--- a/drivers/net/wireless/intel/iwlwifi/iwl-trans.h
+++ b/drivers/net/wireless/intel/iwlwifi/iwl-trans.h
@@ -1006,7 +1006,7 @@ struct iwl_trans {
 
        /* pointer to trans specific struct */
        /*Ensure that this pointer will always be aligned to sizeof pointer */
-       char trans_specific[0] __aligned(sizeof(void *));
+       char trans_specific[] __aligned(sizeof(void *));
 };
 
 const char *iwl_get_cmd_string(struct iwl_trans *trans, u32 id);