MC editor running under root cannot save files not belonging to the root user in /tmp

[birdie]

The error is "Save as: Cannot save file"

OS: Fedora 36
MC: 4.8.28

tmpfs on /tmp type tmpfs (rw,nosuid,nodev,relatime,seclabel)

Yet, in the root session:

echo 123 >> /tmp/testfile

works just fine, so this is a bug in MC.

strace shows

symlink("root@localhost.localdomain.481116", "/tmp/.#testfile") = 0
newfstatat(AT_FDCWD, "/tmp/testfile", {st_mode=S_IFREG|0755, st_size=8341, ...}, 0) = 0
chown("/tmp/testfile", 1000, 1000)       = 0
chmod("/tmp/testfile", 0100755)          = 0
openat(AT_FDCWD, "/tmp/testfile", O_WRONLY|O_CREAT|O_TRUNC, 0100755) = -1 EACCES (Permission denied)

In other directories, i.e. real mounted filesystems, this bug doesn't occur.

[ossi]

the problem is presumably not tmpfs, but the fact that the directory is sticky.
from the openat() manual:

       EACCES Where   O_CREAT   is  specified,  the  protected_fifos  or  pro‐
              tected_regular sysctl is enabled, the file already exists and is
              a  FIFO  or  regular  file, the owner of the file is neither the
              current user nor the owner of the containing directory, and  the
              containing  directory  is  both  world-  or  group-writable  and
              sticky.  For details, see the descriptions of  /proc/sys/fs/pro‐
              tected_fifos and /proc/sys/fs/protected_regular in proc(5).

so presumably you have some security setting enabled which makes root not all-powerful.

[birdie]

I'm using Fedora Linux 36 with default settings.

This warrants an investigation and fix. This is not some odd obscure distro, Fedora is one of the most important Linux distros out there.

[ossi]

i don't think there is a whole lot to investigate here.

things will probably work fine if you select "safe save" save mode.

[birdie]

My root user is not any more limited than what the default Fedora installation has.

If you're OK with the status quo under Fedora and RHEL, as well as their derivatives (we are talking about a dozen of distros) it's worth closing this bug report.