Hi,
On 29-01-15 10:33, Martin Gräßlin wrote:
On Thursday 29 January 2015 10:20:41 Hans de Goede wrote:
Hi All,
A Fedora user has reported problems with MIT-SHM when the xserver
is not running as root. Normal use works fine, but when doing a
"su -" and then starting X apps as root MIT-SHM fails, see this
screenshot:
https://bugzilla.redhat.com/attachment.cgi?id=977933
The culprit is this error:
"Xerror: BadAccess (Attempt to access private resources denied)"
Which makes sense, the shm segment is created by the app running
as root, and the Xserver which is running as a normal user thus
cannot access it, so far this has never been a problem because
X was always running as root :)
I'm tempted to call this a feature rather then a bug, and declaring
this a Qt/KDE bug. I've written MIT SHM using X11 code in the past,
and always installed an error handler, and did an XSync after the
attach to check if the xshm-attach succeed, as it will also fail
when running over the network. I guess qt/kde is using some other
heuristic to determine if it is not running over a network, and
assumes that things will just work when not running over the
network, rather then doing "proper" error checking here.
So to me it seems that Qt/KDE should do "proper" error checking
here and simply fallback to a non shm path in this special case.
thanks for letting me know. Sharing my personal opinion on it:
first of all I consider it an out-of-scope if one runs kcalc as root ;-) That
basically applies to all KDE applications - I do not think we support running
them on root. So breakage here is for me a feature and not a bug.
While I agree that running apps as root in general is a bad idea, I would
not go as far as saying that this breakage is desirable :)
Otherwise it's important to know which application version that is. Whether
it's Qt 4 or Qt 5. The complete interaction with X11 got rewritten for Qt 5
from scratch using XCB. From studying the code in the past I know the xshm
related code supports fallback to non-shm paths. I assume that kcalc is still
a Qt 4 based application in Fedora. If this problem is solved in Qt 5 I guess
nobody would care any more about it.
This is on Fedora 21, so KDE4 (4.14), which AFAIK means qt4.
Regards,
Hans
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