RE: [Patch v4] cifs: Allocate validate negotiation request through kmalloc

[Long Li]

> Subject: Re: [Patch v4] cifs: Allocate validate negotiation request through
> kmalloc
> 
> On 4/20/2018 2:41 PM, Long Li wrote:
> >> Subject: Re: [Patch v4] cifs: Allocate validate negotiation request
> >> through kmalloc
> >>
> >> Looks good, but I have two possibly style-related comments.
> >>
> >> On 4/19/2018 5:38 PM, Long Li wrote:
> >>> From: Long Li <longli@xxxxxxxxxxxxx>
> >>>
> >>> 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@xxxxxxxxxxxx>) 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@xxxxxxxxxxxxx>
> >>> ---
> >>>    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)
> >
> > This is for addressing a prior comment to reduce duplicate code. All
> > the failure paths (after issuing I/O) returning -EIO, there are 5 of
> > them. Set rc to -EIO at the beginning so we donât need to set it multiple
> times.
> 
> Well, ok but now there are semi-duplicate and rather confusing "rc"
> and "ret" local variables, only one of which is actually returned.
> 
> How about a "goto err" with unconditonal -EIO, and just leave the "return 0"
> path alone, like it was? That would be much clearer IMO.

That means we'll have to call kfree(pneg_rsp) and kfree(pneg_inbuf) on the return 0 path,
as well as the return -EIO path.

I'm happy to do that if there is no objection.

> 
> As-is, I needed to read it several times to convince myself the right rc was
> returned.
> 
> Tom,
> 
> 
> >
> >>
> >>> +	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
> >>>
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> 
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> >
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