cifs: cifspdu.h: 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")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/cifs/cifspdu.h b/fs/cifs/cifspdu.h
index 8e15887..593d826 100644 (file)
--- a/fs/cifs/cifspdu.h
+++ b/fs/cifs/cifspdu.h
@@ -1021,7 +1021,7 @@ typedef struct smb_com_writex_req {
        __le16 ByteCount;
        __u8 Pad;               /* BB check for whether padded to DWORD
                                   boundary and optimum performance here */
-       char Data[0];
+       char Data[];
 } __attribute__((packed)) WRITEX_REQ;
 
 typedef struct smb_com_write_req {
@@ -1041,7 +1041,7 @@ typedef struct smb_com_write_req {
        __le16 ByteCount;
        __u8 Pad;               /* BB check for whether padded to DWORD
                                   boundary and optimum performance here */
-       char Data[0];
+       char Data[];
 } __attribute__((packed)) WRITE_REQ;
 
 typedef struct smb_com_write_rsp {
@@ -1306,7 +1306,7 @@ typedef struct smb_com_ntransact_req {
        /* SetupCount words follow then */
        __le16 ByteCount;
        __u8 Pad[3];
-       __u8 Parms[0];
+       __u8 Parms[];
 } __attribute__((packed)) NTRANSACT_REQ;
 
 typedef struct smb_com_ntransact_rsp {
@@ -1523,7 +1523,7 @@ struct file_notify_information {
        __le32 NextEntryOffset;
        __le32 Action;
        __le32 FileNameLength;
-       __u8  FileName[0];
+       __u8  FileName[];
 } __attribute__((packed));
 
 /* For IO_REPARSE_TAG_SYMLINK */
@@ -1536,7 +1536,7 @@ struct reparse_symlink_data {
        __le16  PrintNameOffset;
        __le16  PrintNameLength;
        __le32  Flags;
-       char    PathBuffer[0];
+       char    PathBuffer[];
 } __attribute__((packed));
 
 /* Flag above */
@@ -1553,7 +1553,7 @@ struct reparse_posix_data {
        __le16  ReparseDataLength;
        __u16   Reserved;
        __le64  InodeType; /* LNK, FIFO, CHR etc. */
-       char    PathBuffer[0];
+       char    PathBuffer[];
 } __attribute__((packed));
 
 struct cifs_quota_data {
@@ -1762,7 +1762,7 @@ struct set_file_rename {
        __le32 overwrite;   /* 1 = overwrite dest */
        __u32 root_fid;   /* zero */
        __le32 target_name_len;
-       char  target_name[0];  /* Must be unicode */
+       char  target_name[];  /* Must be unicode */
 } __attribute__((packed));
 
 struct smb_com_transaction2_sfi_req {
@@ -2451,7 +2451,7 @@ struct cifs_posix_acl { /* access conrol list  (ACL) */
        __le16  version;
        __le16  access_entry_count;  /* access ACL - count of entries */
        __le16  default_entry_count; /* default ACL - count of entries */
-       struct cifs_posix_ace ace_array[0];
+       struct cifs_posix_ace ace_array[];
        /* followed by
        struct cifs_posix_ace default_ace_arraay[] */
 } __attribute__((packed));  /* level 0x204 */
@@ -2757,7 +2757,7 @@ typedef struct file_xattr_info {
        /* BB do we need another field for flags? BB */
        __u32 xattr_name_len;
        __u32 xattr_value_len;
-       char  xattr_name[0];
+       char  xattr_name[];
        /* followed by xattr_value[xattr_value_len], no pad */
 } __attribute__((packed)) FILE_XATTR_INFO; /* extended attribute info
                                              level 0x205 */