[quoted lines by rmgls on 2017/09/03 at 18:03 +0200] >I changed the permissions at compile time of the screen executable that I >sent. Screen.c
That isn't necessary. If you start with pure screen source and apply our patch, it will work. If it doesn't then something else is wrong. Tehre's another issue, too. Users have an implicit trust when getting source from official sources. I wouldn't dare run any executable that's been modified by anyone who doesn't have a well established reputation. They're either running this stuff as themselves or as root, and they simply, and rightly, don't want to take any chances. > shmid = shmget( key, size, IPC_CREAT | S_IRWXU | 660); This modified line actually is a case in point. S_IRWXU is a constant that has the octal value 0700, i.e. user-only permissions. That's correct. Adding more bits makes the user's screen viewable by others, which is exactly what he doesn't want. Now let's look at the 660 that's being ored to the correct value. While 660 may be correct chmod syntax, that's only because chmod is expecting an octal value. In C, 660 is being interpreted as a decimal number. 660 decimal works out to being 1224 octal. That's clearly a bad value for the permissions of a shared memory segment. Even if 660 were interpreted as octal, it'd be adding group permissions and that's not what a user would want anyway. So please go back to pure screen source with just our patch applied. I'm going to guess regarding what the problem may be. Screen needs to be started first (at least for the first time) to ensure that the shared memory segment is created before brltty tries to find it. Then brltty must be started, and it must be started by the very same user who started screen. This is nencessary for at least three reasons. First, that's the only way for user-only permissions to allow access. Second, it's the only way for both programs to be implicitly looking for the same shared memory segment. Third, shared memory segments are private by default which means that, without a bit of extra work, another user wouldn't be able to find it. -- Dave Mielke | 2213 Fox Crescent | http://Mielke.cc/ Phone: 1-613-726-0014 | Ottawa, Ontario | http://Mielke.cc/bible/ EMail: [email protected] | Canada K2A 1H7 | The Bible is the very Word of God. _______________________________________________ This message was sent via the BRLTTY mailing list. To post a message, send an e-mail to: [email protected] For general information, go to: http://brltty.com/mailman/listinfo/brltty
