Re: [PATCH][next] smb: smb2pdu.h: Avoid -Wflex-array-member-not-at-end warnings

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 23/04/24 14:15, Steve French wrote:
> This looks reasonably safe (running the usual regression tests on it now).
> 
> Reminds me though that we have to be careful (e.g. the recent fix for
> regression caused by cleanup).

mmh... it seems that the offending commit was never CC'd to the linux-hardening
list, hence it wasn't reviewed by us.

After reviewing both, the offending commit and the fix, both seem to be wrong.

for __packed structs, you should use __struct_group():

__struct_group(network_open_info, group_name, __packed, struct_members);

The _packed in the commit 0268a7cc7fdc is not an attribute, it's the name
for the group. So, it's not actually doing what the submitter thinks it does.

> 
> Thoughts about whether should be sent in rc6 or wait till 6.10?  51
> warnings does sound
> distracting though so might be worth going in sooner rather than later.

There is actually no hurry. :)

Thanks
--
Gustavo

> 
> commit 0268a7cc7fdc47d90b6c18859de7718d5059f6f1
> Author: Namjae Jeon <linkinjeon@kernel.org>
> Date:   Fri Apr 19 23:46:34 2024 +0900
> 
>      ksmbd: common: use struct_group_attr instead of struct_group for
> network_open_info
> 
>      4byte padding cause the connection issue with the applications of MacOS.
>      smb2_close response size increases by 4 bytes by padding, And the smb
>      client of MacOS check it and stop the connection. This patch use
>      struct_group_attr instead of struct_group for network_open_info to use
>       __packed to avoid padding.
> 
> 
> On Tue, Apr 23, 2024 at 1:58 PM Gustavo A. R. Silva
> <gustavo@embeddedor.com> wrote:
>>
>> Hi all,
>>
>> Friendly ping: who can take this, please?
>>
>> Thanks
>> --
>> Gustavo
>>
>> On 11/04/24 09:35, Gustavo A. R. Silva wrote:
>>> -Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
>>> ready to enable it globally.
>>>
>>> So, in order to avoid ending up with a flexible-array member in the
>>> middle of multiple other structs, we use the `__struct_group()` helper
>>> to separate the flexible array from the rest of the members in the
>>> flexible structure, and use the tagged `struct create_context_hdr`
>>> instead of `struct create_context`.
>>>
>>> So, with these changes, fix 51 of the following warnings[1]:
>>>
>>> fs/smb/client/../common/smb2pdu.h:1225:31: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
>>>
>>> Link: https://gist.github.com/GustavoARSilva/772526a39be3dd4db39e71497f0a9893 [1]
>>> Link: https://github.com/KSPP/linux/issues/202
>>> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>>> ---
>>>    fs/smb/client/smb2pdu.h | 12 ++++++------
>>>    fs/smb/common/smb2pdu.h | 33 ++++++++++++++++++---------------
>>>    fs/smb/server/smb2pdu.h | 18 +++++++++---------
>>>    3 files changed, 33 insertions(+), 30 deletions(-)
>>>
>>> diff --git a/fs/smb/client/smb2pdu.h b/fs/smb/client/smb2pdu.h
>>> index c72a3b2886b7..1a02bd9e0c00 100644
>>> --- a/fs/smb/client/smb2pdu.h
>>> +++ b/fs/smb/client/smb2pdu.h
>>> @@ -145,7 +145,7 @@ struct durable_context_v2 {
>>>    } __packed;
>>>
>>>    struct create_durable_v2 {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        struct durable_context_v2 dcontext;
>>>    } __packed;
>>> @@ -167,7 +167,7 @@ struct durable_reconnect_context_v2_rsp {
>>>    } __packed;
>>>
>>>    struct create_durable_handle_reconnect_v2 {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        struct durable_reconnect_context_v2 dcontext;
>>>        __u8   Pad[4];
>>> @@ -175,7 +175,7 @@ struct create_durable_handle_reconnect_v2 {
>>>
>>>    /* See MS-SMB2 2.2.13.2.5 */
>>>    struct crt_twarp_ctxt {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8    Name[8];
>>>        __le64  Timestamp;
>>>
>>> @@ -183,12 +183,12 @@ struct crt_twarp_ctxt {
>>>
>>>    /* See MS-SMB2 2.2.13.2.9 */
>>>    struct crt_query_id_ctxt {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8    Name[8];
>>>    } __packed;
>>>
>>>    struct crt_sd_ctxt {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8    Name[8];
>>>        struct smb3_sd sd;
>>>    } __packed;
>>> @@ -415,7 +415,7 @@ struct smb2_posix_info_parsed {
>>>    };
>>>
>>>    struct smb2_create_ea_ctx {
>>> -     struct create_context ctx;
>>> +     struct create_context_hdr ctx;
>>>        __u8 name[8];
>>>        struct smb2_file_full_ea_info ea;
>>>    } __packed;
>>> diff --git a/fs/smb/common/smb2pdu.h b/fs/smb/common/smb2pdu.h
>>> index 1b594307c9d5..eab9d49c63ba 100644
>>> --- a/fs/smb/common/smb2pdu.h
>>> +++ b/fs/smb/common/smb2pdu.h
>>> @@ -1171,12 +1171,15 @@ struct smb2_server_client_notification {
>>>    #define SMB2_CREATE_FLAG_REPARSEPOINT 0x01
>>>
>>>    struct create_context {
>>> -     __le32 Next;
>>> -     __le16 NameOffset;
>>> -     __le16 NameLength;
>>> -     __le16 Reserved;
>>> -     __le16 DataOffset;
>>> -     __le32 DataLength;
>>> +     /* New members must be added within the struct_group() macro below. */
>>> +     __struct_group(create_context_hdr, hdr, __packed,
>>> +             __le32 Next;
>>> +             __le16 NameOffset;
>>> +             __le16 NameLength;
>>> +             __le16 Reserved;
>>> +             __le16 DataOffset;
>>> +             __le32 DataLength;
>>> +     );
>>>        __u8 Buffer[];
>>>    } __packed;
>>>
>>> @@ -1222,7 +1225,7 @@ struct smb2_create_rsp {
>>>    } __packed;
>>>
>>>    struct create_posix {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8    Name[16];
>>>        __le32  Mode;
>>>        __u32   Reserved;
>>> @@ -1230,7 +1233,7 @@ struct create_posix {
>>>
>>>    /* See MS-SMB2 2.2.13.2.3 and MS-SMB2 2.2.13.2.4 */
>>>    struct create_durable {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        union {
>>>                __u8  Reserved[16];
>>> @@ -1243,14 +1246,14 @@ struct create_durable {
>>>
>>>    /* See MS-SMB2 2.2.13.2.5 */
>>>    struct create_mxac_req {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        __le64 Timestamp;
>>>    } __packed;
>>>
>>>    /* See MS-SMB2 2.2.14.2.5 */
>>>    struct create_mxac_rsp {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        __le32 QueryStatus;
>>>        __le32 MaximalAccess;
>>> @@ -1286,13 +1289,13 @@ struct lease_context_v2 {
>>>    } __packed;
>>>
>>>    struct create_lease {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        struct lease_context lcontext;
>>>    } __packed;
>>>
>>>    struct create_lease_v2 {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        struct lease_context_v2 lcontext;
>>>        __u8   Pad[4];
>>> @@ -1300,7 +1303,7 @@ struct create_lease_v2 {
>>>
>>>    /* See MS-SMB2 2.2.14.2.9 */
>>>    struct create_disk_id_rsp {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        __le64 DiskFileId;
>>>        __le64 VolumeId;
>>> @@ -1309,7 +1312,7 @@ struct create_disk_id_rsp {
>>>
>>>    /* See MS-SMB2 2.2.13.2.13 */
>>>    struct create_app_inst_id {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8 Name[16];
>>>        __le32 StructureSize; /* Must be 20 */
>>>        __u16 Reserved;
>>> @@ -1318,7 +1321,7 @@ struct create_app_inst_id {
>>>
>>>    /* See MS-SMB2 2.2.13.2.15 */
>>>    struct create_app_inst_id_vers {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8 Name[16];
>>>        __le32 StructureSize; /* Must be 24 */
>>>        __u16 Reserved;
>>> diff --git a/fs/smb/server/smb2pdu.h b/fs/smb/server/smb2pdu.h
>>> index bd1d2a0e9203..643f5e1cfe35 100644
>>> --- a/fs/smb/server/smb2pdu.h
>>> +++ b/fs/smb/server/smb2pdu.h
>>> @@ -64,7 +64,7 @@ struct preauth_integrity_info {
>>>    #define SMB2_SESSION_TIMEOUT                (10 * HZ)
>>>
>>>    struct create_durable_req_v2 {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        __le32 Timeout;
>>>        __le32 Flags;
>>> @@ -73,7 +73,7 @@ struct create_durable_req_v2 {
>>>    } __packed;
>>>
>>>    struct create_durable_reconn_req {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        union {
>>>                __u8  Reserved[16];
>>> @@ -85,7 +85,7 @@ struct create_durable_reconn_req {
>>>    } __packed;
>>>
>>>    struct create_durable_reconn_v2_req {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        struct {
>>>                __u64 PersistentFileId;
>>> @@ -96,13 +96,13 @@ struct create_durable_reconn_v2_req {
>>>    } __packed;
>>>
>>>    struct create_alloc_size_req {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        __le64 AllocationSize;
>>>    } __packed;
>>>
>>>    struct create_durable_rsp {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        union {
>>>                __u8  Reserved[8];
>>> @@ -114,7 +114,7 @@ struct create_durable_rsp {
>>>    /* Flags */
>>>    #define SMB2_DHANDLE_FLAG_PERSISTENT        0x00000002
>>>    struct create_durable_v2_rsp {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        __le32 Timeout;
>>>        __le32 Flags;
>>> @@ -122,7 +122,7 @@ struct create_durable_v2_rsp {
>>>
>>>    /* equivalent of the contents of SMB3.1.1 POSIX open context response */
>>>    struct create_posix_rsp {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8    Name[16];
>>>        __le32 nlink;
>>>        __le32 reparse_tag;
>>> @@ -381,13 +381,13 @@ struct smb2_ea_info {
>>>    } __packed; /* level 15 Query */
>>>
>>>    struct create_ea_buf_req {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        struct smb2_ea_info ea;
>>>    } __packed;
>>>
>>>    struct create_sd_buf_req {
>>> -     struct create_context ccontext;
>>> +     struct create_context_hdr ccontext;
>>>        __u8   Name[8];
>>>        struct smb_ntsd ntsd;
>>>    } __packed;
>>
> 
> 
> --
> Thanks,
> 
> Steve