[PATCH][next] cifs: smb2pdu.h: Replace zero-length array with flexible-array member

From: Gustavo A. R. Silva
Date: Mon Mar 09 2020 - 11:41:47 EST

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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>
---
fs/cifs/smb2pdu.h | 38 +++++++++++++++++++-------------------
1 file changed, 19 insertions(+), 19 deletions(-)

diff --git a/fs/cifs/smb2pdu.h b/fs/cifs/smb2pdu.h
index ad14b8505b4d..817bc0531536 100644
--- a/fs/cifs/smb2pdu.h
+++ b/fs/cifs/smb2pdu.h
@@ -182,7 +182,7 @@ struct smb2_symlink_err_rsp {
__le16 PrintNameOffset;
__le16 PrintNameLength;
__le32 Flags;
- __u8 PathBuffer[0];
+ __u8 PathBuffer[];
} __packed;

/* SMB 3.1.1 and later dialects. See MS-SMB2 section 2.2.2.1 */
@@ -210,7 +210,7 @@ struct share_redirect_error_context_rsp {
__le16 Flags;
__le16 TargetType;
__le32 IPAddrCount;
- struct move_dst_ipaddr IpAddrMoveList[0];
+ struct move_dst_ipaddr IpAddrMoveList[];
/* __u8 ResourceName[] */ /* Name of share as counted Unicode string */
} __packed;

@@ -326,7 +326,7 @@ struct smb2_netname_neg_context {
__le16 ContextType; /* 0x100 */
__le16 DataLength;
__le32 Reserved;
- __le16 NetName[0]; /* hostname of target converted to UCS-2 */
+ __le16 NetName[]; /* hostname of target converted to UCS-2 */
} __packed;

#define POSIX_CTXT_DATA_LEN 16
@@ -421,13 +421,13 @@ struct tree_connect_contexts {
__le16 ContextType;
__le16 DataLength;
__le32 Reserved;
- __u8 Data[0];
+ __u8 Data[];
} __packed;

/* Remoted identity tree connect context structures - see MS-SMB2 2.2.9.2.1 */
struct smb3_blob_data {
__le16 BlobSize;
- __u8 BlobData[0];
+ __u8 BlobData[];
} __packed;

/* Valid values for Attr */
@@ -477,14 +477,14 @@ struct remoted_identity_tcon_context {
__le16 DeviceGroups; /* offset to SID_ARRAY_DATA struct */
__le16 UserClaims; /* offset to BLOB_DATA struct */
__le16 DeviceClaims; /* offset to BLOB_DATA struct */
- __u8 TicketInfo[0]; /* variable length buf - remoted identity data */
+ __u8 TicketInfo[]; /* variable length buf - remoted identity data */
} __packed;

struct smb2_tree_connect_req_extension {
__le32 TreeConnectContextOffset;
__le16 TreeConnectContextCount;
__u8 Reserved[10];
- __u8 PathName[0]; /* variable sized array */
+ __u8 PathName[]; /* variable sized array */
/* followed by array of TreeConnectContexts */
} __packed;

@@ -689,7 +689,7 @@ struct smb2_create_req {
__le16 NameLength;
__le32 CreateContextsOffset;
__le32 CreateContextsLength;
- __u8 Buffer[0];
+ __u8 Buffer[];
} __packed;

/*
@@ -727,7 +727,7 @@ struct create_context {
__le16 Reserved;
__le16 DataOffset;
__le32 DataLength;
- __u8 Buffer[0];
+ __u8 Buffer[];
} __packed;

#define SMB2_LEASE_READ_CACHING_HE 0x01
@@ -869,7 +869,7 @@ struct crt_sd_ctxt {
struct resume_key_req {
char ResumeKey[COPY_CHUNK_RES_KEY_SIZE];
__le32 ContextLength; /* MBZ */
- char Context[0]; /* ignored, Windows sets to 4 bytes of zero */
+ char Context[]; /* ignored, Windows sets to 4 bytes of zero */
} __packed;

/* this goes in the ioctl buffer when doing a copychunk request */
@@ -931,7 +931,7 @@ struct reparse_data_buffer {
__le32 ReparseTag;
__le16 ReparseDataLength;
__u16 Reserved;
- __u8 DataBuffer[0]; /* Variable Length */
+ __u8 DataBuffer[]; /* Variable Length */
} __packed;

struct reparse_guid_data_buffer {
@@ -939,7 +939,7 @@ struct reparse_guid_data_buffer {
__le16 ReparseDataLength;
__u16 Reserved;
__u8 ReparseGuid[16];
- __u8 DataBuffer[0]; /* Variable Length */
+ __u8 DataBuffer[]; /* Variable Length */
} __packed;

struct reparse_mount_point_data_buffer {
@@ -950,7 +950,7 @@ struct reparse_mount_point_data_buffer {
__le16 SubstituteNameLength;
__le16 PrintNameOffset;
__le16 PrintNameLength;
- __u8 PathBuffer[0]; /* Variable Length */
+ __u8 PathBuffer[]; /* Variable Length */
} __packed;

#define SYMLINK_FLAG_RELATIVE 0x00000001
@@ -964,7 +964,7 @@ struct reparse_symlink_data_buffer {
__le16 PrintNameOffset;
__le16 PrintNameLength;
__le32 Flags;
- __u8 PathBuffer[0]; /* Variable Length */
+ __u8 PathBuffer[]; /* Variable Length */
} __packed;

/* See MS-FSCC 2.1.2.6 and cifspdu.h for struct reparse_posix_data */
@@ -1066,7 +1066,7 @@ struct smb2_ioctl_req {
__le32 MaxOutputResponse;
__le32 Flags;
__u32 Reserved2;
- __u8 Buffer[0];
+ __u8 Buffer[];
} __packed;

struct smb2_ioctl_rsp {
@@ -1469,7 +1469,7 @@ struct smb3_fs_vol_info {
__le32 VolumeLabelLength; /* includes trailing null */
__u8 SupportsObjects; /* True if eg like NTFS, supports objects */
__u8 Reserved;
- __u8 VolumeLabel[0]; /* variable len */
+ __u8 VolumeLabel[]; /* variable len */
} __packed;

/* partial list of QUERY INFO levels */
@@ -1531,7 +1531,7 @@ struct smb2_file_rename_info { /* encoding of request for level 10 */
__u8 Reserved[7];
__u64 RootDirectory; /* MBZ for network operations (why says spec?) */
__le32 FileNameLength;
- char FileName[0]; /* New name to be assigned */
+ char FileName[]; /* New name to be assigned */
} __packed; /* level 10 Set */

struct smb2_file_link_info { /* encoding of request for level 11 */
@@ -1540,7 +1540,7 @@ struct smb2_file_link_info { /* encoding of request for level 11 */
__u8 Reserved[7];
__u64 RootDirectory; /* MBZ for network operations (why says spec?) */
__le32 FileNameLength;
- char FileName[0]; /* Name to be assigned to new link */
+ char FileName[]; /* Name to be assigned to new link */
} __packed; /* level 11 Set */

struct smb2_file_full_ea_info { /* encoding of response for level 15 */
@@ -1548,7 +1548,7 @@ struct smb2_file_full_ea_info { /* encoding of response for level 15 */
__u8 flags;
__u8 ea_name_length;
__le16 ea_value_length;
- char ea_data[0]; /* \0 terminated name plus value */
+ char ea_data[]; /* \0 terminated name plus value */
} __packed; /* level 15 Set */

/*
--
2.25.0

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