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Merged
merged 6 commits into from
Sep 22, 2024
Merged

argument to change uid/gid #927

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7cd0f6b
argument to change uid/gid
cathugger Jul 11, 2022
72fbe25
attempt to make CodeQL warnings go away
cathugger Dec 8, 2023
87fa0a8
Update cmd/yggdrasil/chuser_unix.go
neilalexander Aug 3, 2024
cb29747
Update cmd/yggdrasil/chuser_unix.go
neilalexander Aug 3, 2024
a2f35a3
Fix imports
neilalexander Aug 3, 2024
fb587b1
Merge branch 'develop' into setuid
neilalexander Sep 22, 2024
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10 changes: 10 additions & 0 deletions cmd/yggdrasil/chuser_other.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
//go:build !aix && !darwin && !dragonfly && !freebsd && !linux && !netbsd && !openbsd && !solaris
// +build !aix,!darwin,!dragonfly,!freebsd,!linux,!netbsd,!openbsd,!solaris

package main

import "errors"

func chuser(user string) error {
return errors.New("setting uid/gid is not supported on this platform")
}
87 changes: 87 additions & 0 deletions cmd/yggdrasil/chuser_unix.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,87 @@
//go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris

package main

import (
"errors"
"fmt"
"math"
osuser "os/user"
"strconv"
"strings"
"syscall"
)

func chuser(user string) error {
group := ""
if i := strings.IndexByte(user, ':'); i >= 0 {
user, group = user[:i], user[i+1:]
}
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Why not just strings.Split(user, ':')?

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IndexByte is probably speediest as Split allocates slice and uses string for splitting.
Cut would probably be more fitting here API niceness wise, but I'm not sure if really worth changing at this point.

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IndexByte is probably speediest as Split allocates slice and uses string for splitting.

This code runs once, it is not a hot path.

Cut would probably be more fitting here API niceness wise, but I'm not sure if really worth changing at this point.

Sure, either way looks cleaner than manual indexing.


u := (*osuser.User)(nil)
g := (*osuser.Group)(nil)

if user != "" {
if _, err := strconv.ParseUint(user, 10, 32); err == nil {
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Why parse it yourself? You can try a name lookup, fallback to UID on error and return if that fails, too, just like getpwnam(3) behaves:

if u, err = osuser.Lookup(user); err != nil {
    if u, err = osuser.LookupId(user); if err != nil {
        return err
    }
}

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this PR introduced as replacement for one that only used numeric IDs so I preserved ability to do chown/chgrp without passwords database file being present in system.
LookupId depends on /etc/passwd being present which is technically not a necessity.

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nvm we do LookupId after this anyway so it's a moot point.

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parsing before potentially IO hitting pw database lookup is probably what i thought back when i wrote this.

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this PR introduced as replacement for one that only used numeric IDs so I preserved ability to do chown/chgrp without passwords database file being present in system.

Do these systems exist? Are they relevant?

LookupId depends on /etc/passwd being present which is technically not a necessity.

The next line uses that function, so this did not go as planned.

So you might as well clean it up, imho.

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as I've mentioned in following comments, yes, this needs pw database anyways, but i prefer minimizing potentially latency introducing tasks (like opening/closing passwd file) even if they're done at init time, so it's guarded by fast parseuint check. it's a matter of taste, eliminating that goes into category of nitpicking IMO.

u, err = osuser.LookupId(user)
if err != nil {
return fmt.Errorf("failed to lookup user by id %q: %v", user, err)
}
} else {
u, err = osuser.Lookup(user)
if err != nil {
return fmt.Errorf("failed to lookup user by name %q: %v", user, err)
}
}
}
if group != "" {
if _, err := strconv.ParseUint(group, 10, 32); err == nil {
g, err = osuser.LookupGroupId(group)
if err != nil {
return fmt.Errorf("failed to lookup group by id %q: %v", user, err)
}
} else {
g, err = osuser.LookupGroup(group)
if err != nil {
return fmt.Errorf("failed to lookup group by name %q: %v", user, err)
}
}
}

if g != nil {
gid, _ := strconv.ParseUint(g.Gid, 10, 32)
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Questionable for this API to return the ID for a known-to-exist group as string...

var err error
if gid < math.MaxInt {
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os/user returns ID strings that were "validated" with strconv.Atoi() which returns int, so this should always be true.

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had to dig deep to confirm this but indeed.
also could probably be <=.
feel free to make a PR if you care for this as this looks like something code being saner internally not something that'll lead to bugs.

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feel free to make a PR if you care for this as this looks like something code being saner internally not something that'll lead to bugs.

Either that or a clean(er) chuser_bsd.go implementation, should I ever start using this option.

Point being: Complexity hides bugs, so code ought to be as simple as possible.

To my eye, multiple Lookup*() and Parse*() are not as trivial to reason about as it could be.

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without digging deep into the source of osuser.LookupId one can't even know whether these ints were checked so I'm not sure complexity argument is even applicable here, it's more complex to verify whether the code is correct if there is no check.
my gut instinct when API doesn't tell stuff like returned ranges of ints to just check myself, because checking more usually catches more bugs than not checking stuff like returns.
IMO if check is eliminated, then strconv.Atoi() check behavior should be documented in comment, as otherwise it won't end up more simple.

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also uint32 vs int is potentially hell on its own due to int being 64bit on 64bit systems and strconv.Atoi() ending up verifying different on 32bit vs 64bit systems but honestly systems just don't use ints as large as these for UIDs/GIDs anyways so i can't really care abt this.

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87fa0a8 apparently was someone's else's change too but I can't argue one way or another abt it.

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to satisfy faulty Code scanning / CodeQL warnings out of all the things

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to satisfy faulty Code scanning / CodeQL warnings out of all the things

This looks related over at #1202:
Screenshot 2024-11-04 at 04-05-21 Set groups when dropping privileges to not leak supplementary group access by klemensn · Pull Request #1202 · yggdrasil-network_yggdrasil-go

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@klemensn klemensn Nov 4, 2024 •
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feel free to make a PR if you care for this as this looks like something code being saner internally not something that'll lead to bugs.

  • -user '' silently ignored and the process continues without error or change in privilege.
  • -user ':' as well.
  • -user :group changes just the group and not the user, contrary to what the usage says:
  -user string
    	user (and, optionally, group) to set UID/GID to

I did fix these now in #1203.

err = syscall.Setgid(int(gid))
} else {
err = errors.New("gid too big")
}

if err != nil {
return fmt.Errorf("failed to setgid %d: %v", gid, err)
}
} else if u != nil {
gid, _ := strconv.ParseUint(u.Gid, 10, 32)
err := syscall.Setgid(int(uint32(gid)))
if err != nil {
return fmt.Errorf("failed to setgid %d: %v", gid, err)
}
}

if u != nil {
uid, _ := strconv.ParseUint(u.Uid, 10, 32)
var err error
if uid < math.MaxInt {
err = syscall.Setuid(int(uid))
} else {
err = errors.New("uid too big")
}

if err != nil {
return fmt.Errorf("failed to setuid %d: %v", uid, err)
}
}

return nil
}
9 changes: 9 additions & 0 deletions cmd/yggdrasil/main.go
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,7 @@ func main() {
getsnet := flag.Bool("subnet", false, "use in combination with either -useconf or -useconffile, outputs your IPv6 subnet")
getpkey := flag.Bool("publickey", false, "use in combination with either -useconf or -useconffile, outputs your public key")
loglevel := flag.String("loglevel", "info", "loglevel to enable")
chuserto := flag.String("user", "", "user (and, optionally, group) to set UID/GID to")
flag.Parse()

done := make(chan struct{})
Expand Down Expand Up @@ -280,6 +281,14 @@ func main() {
<-done
})

// Change user if requested
if *chuserto != "" {
err = chuser(*chuserto)
if err != nil {
panic(err)
}
}

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@klemensn klemensn Nov 2, 2024 •
edited
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The main goroutine changing user/group to drop privileges is racing against others creating a tun(4) interface, raw socket for routing and UNIX socket as control interface, i.e. startup can fail now as yggdrasil may drop to an unprivileged user before having completed all privileged tasks.

# yggdrasil -autoconf -user nobody
2024/11/02 20:24:32 Build name: yggdrasil-go
2024/11/02 20:24:32 Build version: 0.5.9
2024/11/02 20:24:32 Your public key is 82ff9b15b30dc6e460f907cb3aecbe664c024c101efa773b3ecdccf1cb72d818
2024/11/02 20:24:32 Your IPv6 address is 200:fa00:c9d4:99e4:7237:3e0d:f069:8a26
2024/11/02 20:24:32 Your IPv6 subnet is 300:fa00:c9d4:99e4::/64
2024/11/02 20:24:32 Interface name: tun0
2024/11/02 20:24:32 Interface IPv6: 200:fa00:c9d4:99e4:7237:3e0d:f069:8a26/7
2024/11/02 20:24:32 Interface MTU: 16384
2024/11/02 20:24:32 Admin socket failed to listen: listen unix /var/run/yggdrasil.sock: bind: permission denied

Rerun this a few times; sometimes the control socket gets created as root, sometimes it fails to create it as nobody:

$  ls -ld /var/run/
drwxr-xr-x  7 root  wheel  512 Nov  2 20:31 /var/run

// Block until we are told to shut down.
<-ctx.Done()

Expand Down
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