RE: [Patch v3 2/6] cifs: Allocate validate negotiation request through kmalloc

[Long Li]

> Subject: Re: [Patch v3 2/6] cifs: Allocate validate negotiation request through
> kmalloc
> 
> Two comments.
> 
> On 4/17/2018 8:33 PM, Long Li wrote:
> > From: Long Li <longli@xxxxxxxxxxxxx>
> >
> > The data buffer allocated on the stack can't be DMA'ed, and hence
> > can't send through RDMA via SMB Direct.
> 
> This comment is confusing. Any registered memory can be DMA'd, need to
> state the reason for the choice here more clearly.
> 
> >
> > 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@xxxxxxxxxxxx>) Fixed typo in the patch
> > title.
> >
> > Changes in v3:
> > Added "Fixes" to the patch.
> > Changed sizeof() to use *pointer in place of struct.
> >
> > Fixes: ff1c038addc4 ("Check SMB3 dialects against downgrade attacks")
> > Signed-off-by: Long Li <longli@xxxxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > ---
> >   fs/cifs/smb2pdu.c | 59 ++++++++++++++++++++++++++++++--------------
> -----------
> >   1 file changed, 32 insertions(+), 27 deletions(-)
> >
> > diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c index
> > 0f044c4..5582a02 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;
> > +	struct validate_negotiate_info_req *pneg_inbuf;
> >   	struct validate_negotiate_info_rsp *pneg_rsp = NULL;
> >   	u32 rsplen;
> >   	u32 inbuflen; /* max of 4 dialects */ @@ -741,6 +741,9 @@ int
> > smb3_validate_negotiate(const unsigned int xid, struct cifs_tcon *tcon)
> >   	if (tcon->ses->server->rdma)
> >   		return 0;
> >   #endif
> > +	pneg_inbuf = kmalloc(sizeof(*pneg_inbuf), GFP_KERNEL);
> > +	if (!pneg_inbuf)
> > +		return -ENOMEM;
> 
> Why is this a nonblocking allocation? It would seem more robust to use
> GFP_NOFS here.

I agree it makes sense to use GFP_NOFS. 

The choice here is made consistent with all the rest CIFS code allocating protocol request buffers. Maybe we should do another patch to cleanup all those code.

> 
> Tom.
> 
> >
> >   	/* In SMB3.11 preauth integrity supersedes validate negotiate */
> >   	if (tcon->ses->server->dialect == SMB311_PROT_ID) @@ -764,63
> > +767,63 @@ 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->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;
> >   	} 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;
> >   	}
> >
> > -	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;
> >   	}
> >
> > -	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;
> >   	}
> >
> >   	/* 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
> >