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Message-ID: <c8924b83-dfa2-a44c-a425-deb7e03d0bf1@talpey.com>
Date: Fri, 20 Apr 2018 10:55:52 -0400
From: Tom Talpey <tom@...pey.com>
To: longli@...rosoft.com, Steve French <sfrench@...ba.org>,
linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org
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@...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.
> } 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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