On 2/24/20 8:14 AM, Gustavo A. R. Silva wrote:
> 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")
>
> Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> ---
> ...
> 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 f8312a3e5b42..4dc158cf09b8 100644
> --- a/include/scsi/scsi_device.h
> +++ b/include/scsi/scsi_device.h
> @@ -231,7 +231,7 @@ 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) \
> @@ -315,7 +315,7 @@ 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 7a97fb8104cf..e6811ea8f984 100644
> --- a/include/scsi/scsi_host.h
> +++ b/include/scsi/scsi_host.h
> @@ -682,7 +682,7 @@ 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 {
> diff --git a/include/uapi/scsi/scsi_bsg_fc.h b/include/uapi/scsi/scsi_bsg_fc.h
> index 3ae65e93235c..7f5930801f72 100644
> --- a/include/uapi/scsi/scsi_bsg_fc.h
> +++ b/include/uapi/scsi/scsi_bsg_fc.h
> @@ -209,7 +209,7 @@ struct fc_bsg_host_vendor {
> __u64 vendor_id;
>
> /* start of vendor command area */
> - __u32 vendor_cmd[0];
> + __u32 vendor_cmd[];
> };
>
> /* Response:
>
Reviewed-by: Lee Duncan <lduncan@xxxxxxxx>
