> 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 don’t need to set it multiple times.
>
> > + 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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