cifs: fix possible memory corruption in CIFSFindNext

The name_len variable in CIFSFindNext is a signed int that gets set to
the resume_name_len in the cifs_search_info. The resume_name_len however
is unsigned and for some infolevels is populated directly from a 32 bit
value sent by the server.

If the server sends a very large value for this, then that value could
look negative when converted to a signed int. That would make that
value pass the PATH_MAX check later in CIFSFindNext. The name_len would
then be used as a length value for a memcpy. It would then be treated
as unsigned again, and the memcpy scribbles over a ton of memory.

Fix this by making the name_len an unsigned value in CIFSFindNext.

Cc: <stable@kernel.org>
Reported-by: Darren Lavender <dcl@hppine99.gbr.hp.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
CIFSSMBRename(const int xid, struct cifs_tcon *tcon,
	      const char *fromName, const char *toName,
	      const struct nls_table *nls_codepage, int remap)
{
	int rc = 0;
	RENAME_REQ *pSMB = NULL;
	RENAME_RSP *pSMBr = NULL;
	int bytes_returned;
	int name_len, name_len2;
	__u16 count;

	cFYI(1, "In CIFSSMBRename");
renameRetry:
	rc = smb_init(SMB_COM_RENAME, 1, tcon, (void **) &pSMB,
		      (void **) &pSMBr);
	if (rc)
		return rc;

	pSMB->BufferFormat = 0x04;
	pSMB->SearchAttributes =
	    cpu_to_le16(ATTR_READONLY | ATTR_HIDDEN | ATTR_SYSTEM |
			ATTR_DIRECTORY);

	if (pSMB->hdr.Flags2 & SMBFLG2_UNICODE) {
		name_len =
		    cifsConvertToUCS((__le16 *) pSMB->OldFileName, fromName,
				     PATH_MAX, nls_codepage, remap);
		name_len++;	/* trailing null */
		name_len *= 2;
		pSMB->OldFileName[name_len] = 0x04;	/* pad */
	/* protocol requires ASCII signature byte on Unicode string */
		pSMB->OldFileName[name_len + 1] = 0x00;
		name_len2 =
		    cifsConvertToUCS((__le16 *)&pSMB->OldFileName[name_len + 2],
				     toName, PATH_MAX, nls_codepage, remap);
		name_len2 += 1 /* trailing null */  + 1 /* Signature word */ ;
		name_len2 *= 2;	/* convert to bytes */
	} else {	/* BB improve the check for buffer overruns BB */
		name_len = strnlen(fromName, PATH_MAX);
		name_len++;	/* trailing null */
		strncpy(pSMB->OldFileName, fromName, name_len);
		name_len2 = strnlen(toName, PATH_MAX);
		name_len2++;	/* trailing null */
		pSMB->OldFileName[name_len] = 0x04;  /* 2nd buffer format */
		strncpy(&pSMB->OldFileName[name_len + 1], toName, name_len2);
		name_len2++;	/* trailing null */
		name_len2++;	/* signature byte */
	}

	count = 1 /* 1st signature byte */  + name_len + name_len2;
	inc_rfc1001_len(pSMB, count);
	pSMB->ByteCount = cpu_to_le16(count);

	rc = SendReceive(xid, tcon->ses, (struct smb_hdr *) pSMB,
			 (struct smb_hdr *) pSMBr, &bytes_returned, 0);
	cifs_stats_inc(&tcon->num_renames);
	if (rc)
		cFYI(1, "Send error in rename = %d", rc);

	cifs_buf_release(pSMB);

	if (rc == -EAGAIN)
		goto renameRetry;

	return rc;
}

CIFSSMBRename(const int xid, struct cifs_tcon *tcon,
	      const char *fromName, const char *toName,
	      const struct nls_table *nls_codepage, int remap)
{
	int rc = 0;
	RENAME_REQ *pSMB = NULL;
	RENAME_RSP *pSMBr = NULL;
	int bytes_returned;
	int name_len, name_len2;
	__u16 count;

	cFYI(1, "In CIFSSMBRename");
renameRetry:
	rc = smb_init(SMB_COM_RENAME, 1, tcon, (void **) &pSMB,
		      (void **) &pSMBr);
	if (rc)
		return rc;

	pSMB->BufferFormat = 0x04;
	pSMB->SearchAttributes =
	    cpu_to_le16(ATTR_READONLY | ATTR_HIDDEN | ATTR_SYSTEM |
			ATTR_DIRECTORY);

	if (pSMB->hdr.Flags2 & SMBFLG2_UNICODE) {
		name_len =
		    cifsConvertToUCS((__le16 *) pSMB->OldFileName, fromName,
				     PATH_MAX, nls_codepage, remap);
		name_len++;	/* trailing null */
		name_len *= 2;
		pSMB->OldFileName[name_len] = 0x04;	/* pad */
	/* protocol requires ASCII signature byte on Unicode string */
		pSMB->OldFileName[name_len + 1] = 0x00;
		name_len2 =
		    cifsConvertToUCS((__le16 *)&pSMB->OldFileName[name_len + 2],
				     toName, PATH_MAX, nls_codepage, remap);
		name_len2 += 1 /* trailing null */  + 1 /* Signature word */ ;
		name_len2 *= 2;	/* convert to bytes */
	} else {	/* BB improve the check for buffer overruns BB */
		name_len = strnlen(fromName, PATH_MAX);
		name_len++;	/* trailing null */
		strncpy(pSMB->OldFileName, fromName, name_len);
		name_len2 = strnlen(toName, PATH_MAX);
		name_len2++;	/* trailing null */
		pSMB->OldFileName[name_len] = 0x04;  /* 2nd buffer format */
		strncpy(&pSMB->OldFileName[name_len + 1], toName, name_len2);
		name_len2++;	/* trailing null */
		name_len2++;	/* signature byte */
	}

	count = 1 /* 1st signature byte */  + name_len + name_len2;
	inc_rfc1001_len(pSMB, count);
	pSMB->ByteCount = cpu_to_le16(count);

	rc = SendReceive(xid, tcon->ses, (struct smb_hdr *) pSMB,
			 (struct smb_hdr *) pSMBr, &bytes_returned, 0);
	cifs_stats_inc(&tcon->num_renames);
	if (rc)
		cFYI(1, "Send error in rename = %d", rc);

	cifs_buf_release(pSMB);

	if (rc == -EAGAIN)
		goto renameRetry;

	return rc;
}
