iwlegacy: Replace zero-length array with flexible-array

PATCH In review Gustavo A. R. Silva 2 participants 2 messages May 7, 2020 – May 12, 2020 Intel wireless 3945ABG/bg, 4965AGN (iwlegacy)

lore

Share & tools

lore

Gustavo A. R. Silva

author

2020-05-07 18:51 UTC #0 lore raw

PATCH 1/1 iwlegacy: 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 <[email protected]>

---
 drivers/net/wireless/intel/iwlegacy/commands.h     |   22 ++++++++++-----------
 drivers/net/wireless/intel/iwlegacy/iwl-spectrum.h |    4 +--
 2 files changed, 13 insertions(+), 13 deletions(-)

drivers/net/wireless/intel/iwlegacy/commands.h +11 ~~-11~~

index dd744135c956..89c6671b32bc 100644
@@ -203,7 +203,7 @@ struct il_cmd_header {
 	__le16 sequence;
 
 	/* command or response/notification data follows immediately */
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 /**

@@ -1112,7 +1112,7 @@ struct il_wep_cmd {
 	u8 global_key_type;
 	u8 flags;
 	u8 reserved;
-	struct il_wep_key key[0];
+	struct il_wep_key key[];
 } __packed;
 
 #define WEP_KEY_WEP_TYPE 1

@@ -1166,7 +1166,7 @@ struct il3945_rx_frame_stats {
 	u8 agc;
 	__le16 sig_avg;
 	__le16 noise_diff;
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct il3945_rx_frame_hdr {

@@ -1175,7 +1175,7 @@ struct il3945_rx_frame_hdr {
 	u8 reserved1;
 	u8 rate;
 	__le16 len;
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct il3945_rx_frame_end {

@@ -1211,7 +1211,7 @@ struct il4965_rx_non_cfg_phy {
 	__le16 ant_selection;	/* ant A bit 4, ant B bit 5, ant C bit 6 */
 	__le16 agc_info;	/* agc code 0:6, agc dB 7:13, reserved 14:15 */
 	u8 rssi_info[6];	/* we use even entries, 0/2/4 for A/B/C rssi */
-	u8 pad[0];
+	u8 pad[];
 } __packed;
 
 /*

@@ -1409,7 +1409,7 @@ struct il3945_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;
 
 /*

@@ -1511,7 +1511,7 @@ struct il_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;
 
 /* TX command response is sent after *3945* transmission attempts.

@@ -2520,7 +2520,7 @@ struct il3945_scan_cmd {
 	 * for one scan to complete (i.e. receive N_SCAN_COMPLETE)
 	 * before requesting another scan.
 	 */
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 struct il_scan_cmd {

@@ -2564,7 +2564,7 @@ struct il_scan_cmd {
 	 * for one scan to complete (i.e. receive N_SCAN_COMPLETE)
 	 * before requesting another scan.
 	 */
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 /* Can abort will notify by complete notification with abort status. */

@@ -2664,7 +2664,7 @@ struct il3945_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;
 
 struct il_tx_beacon_cmd {

@@ -2672,7 +2672,7 @@ struct il_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;
 
 /******************************************************************************

drivers/net/wireless/intel/iwlegacy/iwl-spectrum.h +2 -2

index a3b490501a70..1e8ab704dbfb 100644
@@ -53,7 +53,7 @@ struct ieee80211_measurement_params {
 struct ieee80211_info_element {
 	u8 id;
 	u8 len;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 struct ieee80211_measurement_request {

@@ -61,7 +61,7 @@ struct ieee80211_measurement_request {
 	u8 token;
 	u8 mode;
 	u8 type;
-	struct ieee80211_measurement_params params[0];
+	struct ieee80211_measurement_params params[];
 } __packed;
 
 struct ieee80211_measurement_report {

Kalle Valo

2020-05-12 08:55 UTC #1 lore raw

Quoted 29 lines · Gustavo A. R. Silva

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.

Quoted 7 lines

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 <[email protected]>

Patch applied to wireless-drivers-next.git, thanks.

8863b1212aab iwlegacy: Replace zero-length array with flexible-array

Signature · 3 lines

https://patchwork.kernel.org/patch/11534705/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches