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Subject: Re: [Patch v4] cifs: Allocate validate negotiation request through
 kmalloc
To:     longli@microsoft.com, Steve French <sfrench@samba.org>,
        linux-cifs@vger.kernel.org, samba-technical@lists.samba.org,
        linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org
References: <20180419213807.3128-1-longli@linuxonhyperv.com>
From:   Tom Talpey <tom@talpey.com>
Message-ID: <c8924b83-dfa2-a44c-a425-deb7e03d0bf1@talpey.com>
Date:   Fri, 20 Apr 2018 10:55:52 -0400
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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.

>   	} 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.

>   	}
>   
> -	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
>