[Xcb] Re: new SELinux protocol reply problem
Jim Gettys
jg at laptop.org
Sat Feb 24 09:39:07 PST 2007
Actually, one or more 32 byte blocks.
The reasons for this is historical (hysterical). malloc/free on certain
platforms (e.g. VMS) were terribly show in the middle '80's. When I say
slow, I mean *really* slow. So by fixing the event size, and keeping a
list of wire events, we could make this go fast.
- Jim
On Sat, 2007-02-24 at 10:17 -0600, Ted X Toth wrote:
> The problem was that xcb in its' read_packet function expects replies to
> be at least 32 bytes long. When I padded the reply the protocol worked.
> Admittedly I'm no xcb expert but this seems a bit broken and at the
> least should be documented. Maybe the xslt could flag when replies
> aren't long enough?
>
> Xavier Toth wrote:
> > I've defined a new protocol GetPropertyContext which I modeled after
> > GetAtomName in xproto.xml but it isn't quite working. Using the code
> > I've include in this message the call to
> > xcb_se_linux_get_property_context_reply in my test client never
> > returns which implies that the client never received the reply or the
> > full reply. At one point I did try setting the reply length to zero
> > and got a reply but the 'context' string returned only contained 20 of
> > 41 bytes sent. What was also curious about this was that as I was
> > debugging and rooting around I could see in the connection in that the
> > entire context string had been received from the server. Is this just
> > a matter of setting the reply length correctly, if so what should I be
> > setting to and why? Also as I look at examples in xproto.xml many
> > requests and replies have a lot of padding that I don't understand the
> > need for can you help me understand why this is necessary?
> >
> >
> > XCB Protocol
> >
> > <xcb header="xselinux" extension-xname="SELinux" extension-name="SELinux"
> > major-version="1" minor-version="0">
> > <import>xproto</import>
> >
> > <request name="ChangePropertyContext" opcode="0">
> > <field type="WINDOW" name="window" />
> > <field type="ATOM" name="property" />
> > <field type="CARD16" name="context_len" />
> > <list type="char" name="context">
> > <fieldref>context_len</fieldref>
> > </list>
> > </request>
> >
> > <request name="GetPropertyContext" opcode="1">
> > <field type="WINDOW" name="window" />
> > <field type="ATOM" name="property" />
> > <reply>
> > <pad bytes="1" />
> > <field type="CARD16" name="context_len" />
> > <list type="CARD8" name="context">
> > <fieldref>context_len</fieldref>
> > </list>
> > </reply>
> > </request>
> >
> > </xcb>
> >
> > Server GetPropertyContext proc.
> >
> > int
> > ProcGetPropertyContext(ClientPtr client)
> > {
> > PropertyPtr pProp, prevProp;
> > unsigned long len, rc;
> > WindowPtr pWin;
> > xcb_se_linux_get_property_context_reply_t reply;
> > Mask access_mode = DixReadAccess;
> > REQUEST(xcb_se_linux_get_property_context_request_t);
> > security_context_t ctx;
> >
> > REQUEST_SIZE_MATCH(xcb_se_linux_get_property_context_request_t);
> > rc = dixLookupWindow(&pWin, stuff->window, client, DixReadAccess);
> > if (rc != Success)
> > return rc;
> >
> > if (!ValidAtom(stuff->property))
> > {
> > client->errorValue = stuff->property;
> > return(BadAtom);
> > }
> >
> > /* Find the property */
> > pProp = wUserProps (pWin);
> > prevProp = (PropertyPtr)NULL;
> > while (pProp)
> > {
> > if (pProp->propertyName == stuff->property)
> > break;
> > prevProp = pProp;
> > pProp = pProp->next;
> > }
> >
> > if (!pProp)
> > return NullPropertyContextReply(client, &reply);
> >
> > switch (XaceHook(XACE_PROPERTY_ACCESS, client, pWin, stuff->property,
> > access_mode))
> > {
> > case XaceErrorOperation:
> > client->errorValue = stuff->property;
> > return BadAtom;;
> > case XaceIgnoreOperation:
> > return NullPropertyContextReply(client, &reply);
> > }
> >
> > /*
> > * Return context value to client
> > */
> > rc = avc_sid_to_context(PropertyGetSIDPriv(pProp), &ctx);
> > if (rc < 0) {
> > FatalError("XSELinux: Failed to get security context!\n");
> > }
> >
> > len = strlen(ctx);
> > reply.response_type = X_Reply;
> > reply.length = (len + 3) >> 2;
> > reply.sequence = client->sequence;
> > reply.context_len = len;
> >
> > WriteToClient(client,
> > sizeof(xcb_se_linux_get_property_context_reply_t), &reply);
> >
> > if (len > 0)
> > {
> > WriteToClient(client, len, (char *)ctx);
> > }
> >
> > freecon(ctx);
> > return(client->noClientException);
> > }
> >
> > Test code.
> >
> >
> > #include <stdio.h>
> >
> > #include <xcb/xcb.h>
> > #include <xcb/xcb_atom.h>
> > #include <xcb/xselinux.h>
> >
> >
> > int
> > main ()
> > {
> >
> > xcb_connection_t *c;
> > xcb_screen_t *screen;
> > xcb_window_t win;
> > char *title = "Hello World !";
> > char *title_icon = "Hello World ! (iconified)";
> >
> > xcb_generic_error_t *generic_error = NULL;
> >
> > xcb_intern_atom_cookie_t atom_cookie;
> > xcb_intern_atom_reply_t *atom_reply;
> > xcb_atom_t atom;
> > xcb_get_atom_name_cookie_t atom_name_cookie;
> > xcb_get_atom_name_reply_t *atom_name_reply;
> >
> > xcb_se_linux_get_property_context_cookie_t prop_cookie;
> > xcb_se_linux_get_property_context_reply_t *prop_reply;
> >
> >
> > /* Open the connection to the X server */
> > c = xcb_connect (NULL, NULL);
> >
> > /* Get the first screen */
> > screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
> >
> > /* Ask for our window's Id */
> > win = xcb_generate_id (c);
> >
> > /* Create the window */
> > xcb_create_window (c, /*
> > Connection */
> > 0, /*
> > depth */
> > win, /* window
> > Id */
> > screen->root, /* parent
> > window */
> > 0, 0, /* x,
> > y */
> > 250, 150, /* width,
> > height */
> > 10, /*
> > border_width */
> > XCB_WINDOW_CLASS_INPUT_OUTPUT, /*
> > class */
> > screen->root_visual, /*
> > visual */
> > 0, NULL); /* masks, not
> > used */
> >
> > /* Set the title of the window */
> > xcb_change_property (c, XCB_PROP_MODE_REPLACE, win,
> > WM_NAME, STRING, 8,
> > strlen (title), title);
> >
> > /* Set the title of the window icon */
> > xcb_change_property (c, XCB_PROP_MODE_REPLACE, win,
> > WM_ICON_NAME, STRING, 8,
> > strlen(title_icon), title_icon);
> >
> > /* Map the window on the screen */
> > xcb_map_window (c, win);
> >
> > xcb_flush (c);
> >
> > atom = xcb_intern_atom_reply (c,
> > xcb_intern_atom (c,
> > 0,
> > strlen("WM_NAME"),
> > "WM_NAME"),
> > NULL)->atom;
> >
> > atom_name_cookie = xcb_get_atom_name(c, atom);
> > atom_name_reply = xcb_get_atom_name_reply(c, atom_name_cookie,
> > &generic_error);
> > fprintf(stderr, "atom %d %s\n",
> > xcb_get_atom_name_name_length(atom_name_reply),
> > (char*)xcb_get_atom_name_name(atom_name_reply));
> >
> > fprintf(stderr, "xcb_se_linux_get_property_context_reply_t %d\n",
> > sizeof(xcb_se_linux_get_property_context_reply_t));
> > prop_cookie = xcb_se_linux_get_property_context(c, win, WM_NAME);
> > prop_reply = xcb_se_linux_get_property_context_reply(c, prop_cookie,
> > &generic_error);
> >
> > if ((generic_error != NULL) || (prop_reply == NULL)) {
> > free(generic_error);
> > return 0;
> > }
> >
> > int num_ret =
> > xcb_se_linux_get_property_context_context_length(prop_reply);
> > char *retval = xcb_se_linux_get_property_context_context(prop_reply);
> >
> > fprintf(stderr, "Context %d %s %d\n", num_ret, retval, strlen(retval));
> >
> > while (1) {}
> >
> >
> > return 0;
> > }
> >
>
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--
Jim Gettys
One Laptop Per Child
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