Re: [PATCH] scsi: Replace zero-length array with flexible-array member
From: Gustavo A. R. Silva
Date: Mon Feb 24 2020 - 11:39:36 EST
On 2/24/20 10:30, Lee Duncan wrote:
> 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>
>
Thanks, Lee.
--
Gustavo