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Message-ID: <CAKywueRbMHOd5vi7f-z2njS6cygmJaxzjAr8TX+vgKXio5JijQ@mail.gmail.com>
Date: Fri, 20 Apr 2018 10:58:11 -0700
From: Pavel Shilovsky <piastryyy@...il.com>
To: Tom Talpey <tom@...pey.com>
Cc: Long Li <longli@...rosoft.com>, Steve French <sfrench@...ba.org>,
linux-cifs <linux-cifs@...r.kernel.org>,
samba-technical <samba-technical@...ts.samba.org>,
Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-rdma@...r.kernel.org
Subject: Re: [Patch v4] cifs: Allocate validate negotiation request through kmalloc
2018-04-20 7:55 GMT-07:00 Tom Talpey <tom@...pey.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@...rosoft.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@...lanox.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@...rosoft.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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