Red Hat Bugzilla – Bug 24844
/usr/libexec/pt_chown has wrong permissions
Last modified: 2016-11-24 10:05:03 EST
Symptoms: run mc under non-privileged user account and you are unable to
use subshell there.
Reason: after glibc-common-2.2-12 (or glibc before splittting it to two
rpms) install, the file permissions for /usr/libexec/pt_chown are set
incorrectly. They are 600, while they must be 755, and pt_chown must be
suid root also.
Consequences: glibc always fails in grantpt() returning ENOEXEC in errno,
because of the incorrect file permisions in pt_chown
Why? Because /usr/libexec/pt_chown is a helper app used by glibc to change
ownership of the slave end of a pseudo-terminal. This is what grantpt()
Since permissions are set to 600 on pt_chown, glibc can't execute it from
the grantpt() function, and hence we get ENOEXEC.
This is intentional. We don't want to ship an unneeded suid program
(it is not needed when you have /dev/pts mounted) but we ship it there so
folks who explicitely don't want to use /dev/pts (installer sets up /dev/pts
mounting btw) can chmod 4755 /usr/libexec/pt_chown themselves.
/usr/libexec/pt_chown had 600 permissions for long time already, I've just
checked glibc-2.1.92-14 which shipped in 7.0 originally and it has the same
mc spawns a subshell when I login as normal user on console without any problems.
How about adding post-install script to glibc-common, which detects absence of
/dev/pts and sets proper permissions to pt_chown?
Your mc works fine either because you have /dev/pts or because permissions on
pt_chown are 755/suid. In my case I did not have /dev/pts and glibc-common did
not detect it during install and mc wouldn't spawn subshell. Because without
/dev/pts glibc needs pt_chown with access rights 755, but again, glibc-common
doesn't do that, EVEN when there is no /dev/pts.
So this is rather a bug anyway. glibc-common must detect whether there is
/dev/pts and act accordingly, adjusting permissions for /usr/libexec/pt_chown.
NOTE: I didn't notice /dev/pts in my mount output:
[pirks@alg158ghy74l ~]$ mount
/dev/hda8 on / type ext2 (rw)
none on /proc type proc (rw)
/dev/hda7 on /mnt/fat type vfat (rw,uid=500,gid=500)
/dev/hda3 on /mnt/fat2 type vfat (rw,uid=500,gid=500)
/dev/hda5 on /mnt/ext2 type ext2 (rw)
[pirks@alg158ghy74l ~]$ ls /dev/pts
ls: /dev/pts: No such file or directory
So now the question is why installer did not set up /dev/pts on my system, which
is another issue.
Is there a way I can check if /dev/pts was installed by glibc-common? A special
file somewhere or something like? OK, I can check the post-install script in a
while. If I find something interesting, I'll post it here.