Typo in newuidmap newgidmap man pages file descriptor sections

[igo95862]

https://github.com/shadow-maint/shadow/blob/f7fe4c59781fde33e112be2cfdec44b84fda6497/man/newuidmap.1.xml#L122-L124

https://github.com/shadow-maint/shadow/blob/f7fe4c59781fde33e112be2cfdec44b84fda6497/man/newgidmap.1.xml#L122-L124

Both man pages when explaining passing the file descriptors mention that the descriptor has to be opened file /proc/[pid[. It is supposed to be /proc/[pid]/ directory? Is it supposed to be /proc/[pid]/uid_map? Or is it a pidfd?

[hallyn]

It's meant to be a pidfd or an fd to the directory /proc/pid. (per https://man7.org/linux/man-pages/man2/pidfd_open.2.html ,

       The pidfd_open() system call is the preferred way of obtaining a
       PID file descriptor for an already existing process.  The
       alternative is to obtain a file descriptor by opening a /proc/pid
       directory. 

)

[hallyn]

Having said that, I see that the result of pidfd_open will have a different device type, and therefore pidfd_open result actually won't work here.

[igo95862]

So the issue here is that first one of the square brackets is in wrong direction and second is that it should spell that it should be the directory that file descriptor should refer to.

[hallyn]

And the third is that right now it won't actually work with a pidfd. The code should be fixed to try check for and handle a pidfd. Or, the docs updated to specify that only open(/proc/pid, O_RDONLY) result is valid right now.

For fixing it to work with pidfd, @brauner suggested (thanks!):

• Parse the PID from /proc/self/fdinfo/N
• Open /proc/PID/Xid_map
• Send 0 signal to pidfd to verify it hasn't been recycled

[hallyn]

@igo95862 I assume based on your last comment that you are not interested in posting a pr for this, right?

[igo95862]

@igo95862 I assume based on your last comment that you are not interested in posting a pr for this, right?

I can if you want. (but it will have to wait until weekend)

I stumbled on this while working on my Python namespaces library.