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From:   Pavel Shilovsky <piastryyy@gmail.com>
Date:   Fri, 20 Apr 2018 10:58:11 -0700
Message-ID: <CAKywueRbMHOd5vi7f-z2njS6cygmJaxzjAr8TX+vgKXio5JijQ@mail.gmail.com>
Subject: Re: [Patch v4] cifs: Allocate validate negotiation request through kmalloc
To:     Tom Talpey <tom@talpey.com>
Cc:     Long Li <longli@microsoft.com>, Steve French <sfrench@samba.org>,
        linux-cifs <linux-cifs@vger.kernel.org>,
        samba-technical <samba-technical@lists.samba.org>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-rdma@vger.kernel.org
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2018-04-20 7:55 GMT-07:00 Tom Talpey <tom@talpey.com>:
> Looks good, but I have two possibly style-related comments.
>
>
> On 4/19/2018 5:38 PM, Long Li wrote:
>>
>> From: Long Li <longli@microsoft.com>
>>
>> The data buffer allocated on the stack can't be DMA'ed, ib_dma_map_page
>> will
>> return an invalid DMA address for a buffer on stack. Even worse, this
>> incorrect address can't be detected by ib_dma_mapping_error. Sending data
>> from this address to hardware will not fail, but the remote peer will get
>> junk data.
>>
>> Fix this by allocating the request on the heap in smb3_validate_negotiate.
>>
>> Changes in v2:
>> Removed duplicated code on freeing buffers on function exit.
>> (Thanks to Parav Pandit <parav@mellanox.com>)
>> Fixed typo in the patch title.
>>
>> Changes in v3:
>> Added "Fixes" to the patch.
>> Changed several sizeof() to use *pointer in place of struct.
>>
>> Changes in v4:
>> Added detailed comments on the failure through RDMA.
>> Allocate request buffer using GPF_NOFS.
>> Fixed possible memory leak.
>>
>> Fixes: ff1c038addc4 ("Check SMB3 dialects against downgrade attacks")
>> Signed-off-by: Long Li <longli@microsoft.com>
>> ---
>>   fs/cifs/smb2pdu.c | 61
>> ++++++++++++++++++++++++++++++-------------------------
>>   1 file changed, 33 insertions(+), 28 deletions(-)
>>
>> diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
>> index 0f044c4..caa2a1e 100644
>> --- a/fs/cifs/smb2pdu.c
>> +++ b/fs/cifs/smb2pdu.c
>> @@ -729,8 +729,8 @@ SMB2_negotiate(const unsigned int xid, struct cifs_ses
>> *ses)
>>     int smb3_validate_negotiate(const unsigned int xid, struct cifs_tcon
>> *tcon)
>>   {
>> -       int rc = 0;
>> -       struct validate_negotiate_info_req vneg_inbuf;
>> +       int ret, rc = -EIO;
>
>
> Seems awkward to have "rc" and "ret", and based on the code below I
> don't see why two variables are needed. Simplify? (see later comment)
>
>
>> +       struct validate_negotiate_info_req *pneg_inbuf;
>>         struct validate_negotiate_info_rsp *pneg_rsp = NULL;
>>         u32 rsplen;
>>         u32 inbuflen; /* max of 4 dialects */
>> @@ -741,7 +741,6 @@ int smb3_validate_negotiate(const unsigned int xid,
>> struct cifs_tcon *tcon)
>>         if (tcon->ses->server->rdma)
>>                 return 0;
>>   #endif
>> -
>>         /* In SMB3.11 preauth integrity supersedes validate negotiate */
>>         if (tcon->ses->server->dialect == SMB311_PROT_ID)
>>                 return 0;
>> @@ -764,63 +763,67 @@ int smb3_validate_negotiate(const unsigned int xid,
>> struct cifs_tcon *tcon)
>>         if (tcon->ses->session_flags & SMB2_SESSION_FLAG_IS_NULL)
>>                 cifs_dbg(VFS, "Unexpected null user (anonymous) auth flag
>> sent by server\n");
>>   -     vneg_inbuf.Capabilities =
>> +       pneg_inbuf = kmalloc(sizeof(*pneg_inbuf), GFP_NOFS);
>> +       if (!pneg_inbuf)
>> +               return -ENOMEM;
>> +
>> +       pneg_inbuf->Capabilities =
>>
>> cpu_to_le32(tcon->ses->server->vals->req_capabilities);
>> -       memcpy(vneg_inbuf.Guid, tcon->ses->server->client_guid,
>> +       memcpy(pneg_inbuf->Guid, tcon->ses->server->client_guid,
>>                                         SMB2_CLIENT_GUID_SIZE);
>>         if (tcon->ses->sign)
>> -               vneg_inbuf.SecurityMode =
>> +               pneg_inbuf->SecurityMode =
>>                         cpu_to_le16(SMB2_NEGOTIATE_SIGNING_REQUIRED);
>>         else if (global_secflags & CIFSSEC_MAY_SIGN)
>> -               vneg_inbuf.SecurityMode =
>> +               pneg_inbuf->SecurityMode =
>>                         cpu_to_le16(SMB2_NEGOTIATE_SIGNING_ENABLED);
>>         else
>> -               vneg_inbuf.SecurityMode = 0;
>> +               pneg_inbuf->SecurityMode = 0;
>>         if (strcmp(tcon->ses->server->vals->version_string,
>>                 SMB3ANY_VERSION_STRING) == 0) {
>> -               vneg_inbuf.Dialects[0] = cpu_to_le16(SMB30_PROT_ID);
>> -               vneg_inbuf.Dialects[1] = cpu_to_le16(SMB302_PROT_ID);
>> -               vneg_inbuf.DialectCount = cpu_to_le16(2);
>> +               pneg_inbuf->Dialects[0] = cpu_to_le16(SMB30_PROT_ID);
>> +               pneg_inbuf->Dialects[1] = cpu_to_le16(SMB302_PROT_ID);
>> +               pneg_inbuf->DialectCount = cpu_to_le16(2);
>>                 /* structure is big enough for 3 dialects, sending only 2
>> */
>>                 inbuflen = sizeof(struct validate_negotiate_info_req) - 2;
>
>
> The "- 2" is a little confusing here. This was existing code, but I
> suggest you change this to a sizeof (u16) construct for consistency.
> It's reducing by the length of a single Dialects[n] entry.

I would suggest to make it "- sizeof(pneg_inbuf->Dialects[0])"...

>
>>         } else if (strcmp(tcon->ses->server->vals->version_string,
>>                 SMBDEFAULT_VERSION_STRING) == 0) {
>> -               vneg_inbuf.Dialects[0] = cpu_to_le16(SMB21_PROT_ID);
>> -               vneg_inbuf.Dialects[1] = cpu_to_le16(SMB30_PROT_ID);
>> -               vneg_inbuf.Dialects[2] = cpu_to_le16(SMB302_PROT_ID);
>> -               vneg_inbuf.DialectCount = cpu_to_le16(3);
>> +               pneg_inbuf->Dialects[0] = cpu_to_le16(SMB21_PROT_ID);
>> +               pneg_inbuf->Dialects[1] = cpu_to_le16(SMB30_PROT_ID);
>> +               pneg_inbuf->Dialects[2] = cpu_to_le16(SMB302_PROT_ID);
>> +               pneg_inbuf->DialectCount = cpu_to_le16(3);
>>                 /* structure is big enough for 3 dialects */
>>                 inbuflen = sizeof(struct validate_negotiate_info_req);
>>         } else {
>>                 /* otherwise specific dialect was requested */
>> -               vneg_inbuf.Dialects[0] =
>> +               pneg_inbuf->Dialects[0] =
>>                         cpu_to_le16(tcon->ses->server->vals->protocol_id);
>> -               vneg_inbuf.DialectCount = cpu_to_le16(1);
>> +               pneg_inbuf->DialectCount = cpu_to_le16(1);
>>                 /* structure is big enough for 3 dialects, sending only 1
>> */
>>                 inbuflen = sizeof(struct validate_negotiate_info_req) - 4;
>
>
>
> Ditto previous sizeof (u16) comment, with a *2 this case.

... and "- 2 * sizeof(pneg_inbuf->Dialects[0])" respectively.

>
>>         }
>>   -     rc = SMB2_ioctl(xid, tcon, NO_FILE_ID, NO_FILE_ID,
>> +       ret = SMB2_ioctl(xid, tcon, NO_FILE_ID, NO_FILE_ID,
>>                 FSCTL_VALIDATE_NEGOTIATE_INFO, true /* is_fsctl */,
>> -               (char *)&vneg_inbuf, sizeof(struct
>> validate_negotiate_info_req),
>> +               (char *)pneg_inbuf, sizeof(*pneg_inbuf),
>>                 (char **)&pneg_rsp, &rsplen);
>>   -     if (rc != 0) {
>> -               cifs_dbg(VFS, "validate protocol negotiate failed: %d\n",
>> rc);
>> -               return -EIO;
>> +       if (ret) {
>> +               cifs_dbg(VFS, "validate protocol negotiate failed: %d\n",
>> ret);
>> +               goto out_free_inbuf;
>>         }
>
>
> Why not leave "rc" alone, and set its value to -EIO before the goto
> if the ioctl fails? That will simplify and make the code much more
> readable IMO.
>
>>   -     if (rsplen != sizeof(struct validate_negotiate_info_rsp)) {
>> +       if (rsplen != sizeof(*pneg_rsp)) {
>>                 cifs_dbg(VFS, "invalid protocol negotiate response size:
>> %d\n",
>>                          rsplen);
>>                 /* relax check since Mac returns max bufsize allowed on
>> ioctl */
>>                 if ((rsplen > CIFSMaxBufSize)
>>                      || (rsplen < sizeof(struct
>> validate_negotiate_info_rsp)))
>> -                       goto err_rsp_free;
>> +                       goto out_free_rsp;
>>         }
>
>
> Would need an rc = -EIO here too if above comment is accepted.
>
> Tom.
>
>>         /* check validate negotiate info response matches what we got
>> earlier */
>> @@ -838,14 +841,16 @@ int smb3_validate_negotiate(const unsigned int xid,
>> struct cifs_tcon *tcon)
>>         /* validate negotiate successful */
>>         cifs_dbg(FYI, "validate negotiate info successful\n");
>> -       kfree(pneg_rsp);
>> -       return 0;
>> +       rc = 0;
>> +       goto out_free_rsp;
>>     vneg_out:
>>         cifs_dbg(VFS, "protocol revalidation - security settings
>> mismatch\n");
>> -err_rsp_free:
>> +out_free_rsp:
>>         kfree(pneg_rsp);
>> -       return -EIO;
>> +out_free_inbuf:
>> +       kfree(pneg_inbuf);
>> +       return rc;
>>   }
>>     enum securityEnum
>>
> --
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