| Message ID | 20200306221740.GA31410@embeddedor (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [next] cifs: cifspdu.h: Replace zero-length array with flexible-array member | expand |
merged into cifs-2.6.git for-next On Fri, Mar 6, 2020 at 5:01 PM Gustavo A. R. Silva <gustavo@embeddedor.com> 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@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 >
On 3/7/20 14:04, Steve French wrote: > merged into cifs-2.6.git for-next > Thanks, Steve. -- Gustavo
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 */
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(-)