scsi: Replace zero-length array with flexible-array member

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]

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")

Link: https://lore.kernel.org/r/20200224161406.GA21454@embeddedor
Reviewed-by: Lee Duncan <lduncan@suse.com>
Reviewed-by: Satish Kharat <satishkh@cisco.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

6 files changed, 14 insertions, 14 deletions

diff --git a/include/scsi/iscsi_if.h b/include/scsi/iscsi_if.h
index 92b11c7e0b4f..b0e240b10bf9 100644
--- a/include/scsi/iscsi_if.h
+++ b/include/scsi/iscsi_if.h
@@ -311,7 +311,7 @@ enum iscsi_param_type {
 struct iscsi_param_info {
 	uint32_t len;		/* Actual length of the param value */
 	uint16_t param;		/* iscsi param */
-	uint8_t value[0];	/* length sized value follows */
+	uint8_t value[];	/* length sized value follows */
 } __packed;
 
 struct iscsi_iface_param_info {
@@ -320,7 +320,7 @@ struct iscsi_iface_param_info {
 	uint16_t param;		/* iscsi param value */
 	uint8_t iface_type;	/* IPv4 or IPv6 */
 	uint8_t param_type;	/* iscsi_param_type */
-	uint8_t value[0];	/* length sized value follows */
+	uint8_t value[];	/* length sized value follows */
 } __packed;
 
 /*
@@ -697,7 +697,7 @@ enum iscsi_flashnode_param {
 struct iscsi_flashnode_param_info {
 	uint32_t len;		/* Actual length of the param */
 	uint16_t param;		/* iscsi param value */
-	uint8_t value[0];	/* length sized value follows */
+	uint8_t value[];	/* length sized value follows */
 } __packed;
 
 enum iscsi_discovery_parent_type {
@@ -815,7 +815,7 @@ struct iscsi_stats {
 	 * up to ISCSI_STATS_CUSTOM_MAX
 	 */
 	uint32_t custom_length;
-	struct iscsi_stats_custom custom[0]
+	struct iscsi_stats_custom custom[]
 		__attribute__ ((aligned (sizeof(uint64_t))));
 };
 
@@ -946,7 +946,7 @@ struct iscsi_offload_host_stats {
 	 * up to ISCSI_HOST_STATS_CUSTOM_MAX
 	 */
 	uint32_t custom_length;
-	struct iscsi_host_stats_custom custom[0]
+	struct iscsi_host_stats_custom custom[]
 		__aligned(sizeof(uint64_t));
 };
 
diff --git a/include/scsi/scsi_bsg_iscsi.h b/include/scsi/scsi_bsg_iscsi.h
index fa0c820a1663..6b8128005af8 100644
--- a/include/scsi/scsi_bsg_iscsi.h
+++ b/include/scsi/scsi_bsg_iscsi.h
@@ -52,7 +52,7 @@ struct iscsi_bsg_host_vendor {
 	uint64_t vendor_id;
 
 	/* start of vendor command area */
-	uint32_t vendor_cmd[0];
+	uint32_t vendor_cmd[];
 };
 
 /* Response:
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index f146a4557787..579e24c92f2f 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -230,7 +230,7 @@ struct scsi_device {
 	struct mutex		state_mutex;
 	enum scsi_device_state sdev_state;
 	struct task_struct	*quiesced_by;
-	unsigned long		sdev_data[0];
+	unsigned long		sdev_data[];
 } __attribute__((aligned(sizeof(unsigned long))));
 
 #define	to_scsi_device(d)	\
@@ -314,7 +314,7 @@ struct scsi_target {
 	char			scsi_level;
 	enum scsi_target_state	state;
 	void 			*hostdata; /* available to low-level driver */
-	unsigned long		starget_data[0]; /* for the transport */
+	unsigned long		starget_data[]; /* for the transport */
 	/* starget_data must be the last element!!!! */
 } __attribute__((aligned(sizeof(unsigned long))));
 
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 7464394e7d01..822e8cda8d9b 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -683,7 +683,7 @@ struct Scsi_Host {
 	 * and also because some compilers (m68k) don't automatically force
 	 * alignment to a long boundary.
 	 */
-	unsigned long hostdata[0]  /* Used for storage of host specific stuff */
+	unsigned long hostdata[]  /* Used for storage of host specific stuff */
 		__attribute__ ((aligned (sizeof(unsigned long))));
 };
 
diff --git a/include/scsi/scsi_ioctl.h b/include/scsi/scsi_ioctl.h
index 4fe69d863b5d..b465799f4d2d 100644
--- a/include/scsi/scsi_ioctl.h
+++ b/include/scsi/scsi_ioctl.h
@@ -27,7 +27,7 @@ struct scsi_device;
 typedef struct scsi_ioctl_command {
 	unsigned int inlen;
 	unsigned int outlen;
-	unsigned char data[0];
+	unsigned char data[];
 } Scsi_Ioctl_Command;
 
 typedef struct scsi_idlun {
diff --git a/include/scsi/srp.h b/include/scsi/srp.h
index 9220758d5087..177d8026e96f 100644
--- a/include/scsi/srp.h
+++ b/include/scsi/srp.h
@@ -109,7 +109,7 @@ struct srp_direct_buf {
 struct srp_indirect_buf {
 	struct srp_direct_buf	table_desc;
 	__be32			len;
-	struct srp_direct_buf	desc_list[0];
+	struct srp_direct_buf	desc_list[];
 } __attribute__((packed));
 
 /* Immediate data buffer descriptor as defined in SRP2. */
@@ -244,7 +244,7 @@ struct srp_cmd {
 	u8	reserved4;
 	u8	add_cdb_len;
 	u8	cdb[16];
-	u8	add_data[0];
+	u8	add_data[];
 };
 
 enum {
@@ -274,7 +274,7 @@ struct srp_rsp {
 	__be32	data_in_res_cnt;
 	__be32	sense_data_len;
 	__be32	resp_data_len;
-	u8	data[0];
+	u8	data[];
 } __attribute__((packed));
 
 struct srp_cred_req {
@@ -306,7 +306,7 @@ struct srp_aer_req {
 	struct scsi_lun	lun;
 	__be32	sense_data_len;
 	u32	reserved3;
-	u8	sense_data[0];
+	u8	sense_data[];
 } __attribute__((packed));
 
 struct srp_aer_rsp {