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Subject[PATCH][next] 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>
---
fs/cifs/cifspdu.h | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/fs/cifs/cifspdu.h b/fs/cifs/cifspdu.h
index 8e15887d1f1f..593d826820c3 100644
--- 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 */
--
2.25.0
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