testing/ostest: extend multiuser identity and permission tests

[Abhishekmishra2808]

Summary

Extends testing/ostest/multiuser.c with regression tests for POSIX credential switching (getresuid/setreuid, saved set-UID/GID) and file/IPC permission enforcement. Enhances NSH id to print real, effective, and saved UID/GID in Linux-style format. Creates a temporary passwd file at build-configured path before getpwnam() checks, so sim:ostest multiuser tests do not need a pre-built /etc/passwd.

Impact

Enables automated validation of multi-user identity and permission behavior when CONFIG_TESTING_OSTEST_MULTIUSER and CONFIG_SCHED_USER_IDENTITY are enabled. The id command output is richer but backward-compatible (same command, more detail). No effect on builds that do not enable multiuser ostest options.

Testing

user_main: multi-user test
multiuser_test: start
multiuser: effective UID/GID switching
  PASS: initial uid == 0
  PASS: initial euid == 0
  PASS: initial gid == 0
  PASS: initial egid == 0
  PASS: root seteuid(1000)
  PASS: euid after seteuid(1000) == 1000
  PASS: root seteuid(0) restore
  PASS: euid restored to 0 == 0
  PASS: root setegid(2000)
  PASS: egid after setegid(2000) == 2000
  PASS: root setegid(0) restore
  PASS: egid restored to 0 == 0
multiuser: getresuid/getresgid and setreuid/setregid
  PASS: getresuid(initial)
  PASS: initial real uid == 0
  PASS: initial eff uid == 0
  PASS: initial saved uid == 0
  PASS: getresgid(initial)
  PASS: initial real gid == 0
  PASS: initial eff gid == 0
  PASS: initial saved gid == 0
  PASS: root setreuid(-1,1000)
  PASS: real uid after setreuid(-1,1000) == 0
  PASS: eff uid after setreuid(-1,1000) == 1000
  PASS: saved uid after setreuid(-1,1000) == 1000
  PASS: non-root setreuid(2000,-1) denied errno=1
  PASS: setreuid(-1,0) drop effective
  PASS: root setreuid(0,-1) restore
  PASS: real uid restored == 0
  PASS: eff uid restored == 0
  PASS: saved uid restored == 0
  PASS: root setregid(-1,1000)
  PASS: real gid after setregid(-1,1000) == 0
  PASS: eff gid after setregid(-1,1000) == 1000
  PASS: saved gid after setregid(-1,1000) == 1000
  PASS: non-root setregid(2000,-1) denied errno=1
  PASS: setregid(-1,0) drop effective
  PASS: root setregid(0,-1) restore
multiuser: setreuid(1000,1000) full assignment (child task)
  PASS: root setreuid(1000,1000)
  PASS: getresuid(after setreuid)
  PASS: real uid after setreuid == 1000
  PASS: eff uid after setreuid == 1000
  PASS: saved uid after setreuid == 1000
multiuser_resuid_child: 0 failure(s)
  PASS: mu_resuid child completed successfully
  PASS: parent euid after resuid child == 0
  PASS: parent egid after resuid child == 0
multiuser: saved set-UID/GID semantics (child task)
multiuser_suid_child: saved set-UID/GID semantics
  PASS: setuid(1000) as root
  PASS: uid after setuid(1000) == 1000
  PASS: euid after setuid(1000) == 1000
  PASS: non-root seteuid(0) denied errno=1
  PASS: euid unchanged after denied seteuid(0) == 1000
  PASS: non-root seteuid(1000)
  PASS: root-group setegid(2000)
  PASS: egid after setegid(2000) == 2000
  PASS: root-group setegid(0) restore
  PASS: setgid(3000)
  PASS: gid after setgid(3000) == 3000
  PASS: egid after setgid(3000) == 3000
  PASS: non-root setegid(0) denied errno=1
  PASS: egid unchanged after denied setegid(0) == 3000
multiuser_suid_child: 0 failure(s)
  PASS: mu_suid child completed successfully
  PASS: parent euid after child == 0
  PASS: parent egid after child == 0
multiuser: pseudoFS chmod/chown/open permissions
  PASS: /ostest_mu_perm owner 0:0
  PASS: root chmod(0600)
  PASS: non-owner chmod(0777) denied errno=1
  PASS: non-root chown(0,0) denied errno=1
  PASS: root chown to 1000:1000
  PASS: /ostest_mu_perm owner 1000:1000
  PASS: owner chmod(0777)
  PASS: /ostest_mu_secret owner 0:0
  PASS: open(/ostest_mu_secret) denied with EACCES
  PASS: open(/ostest_mu_secret) allowed
  PASS: /ostest_mu_user owner 1000:1000
  PASS: open(/ostest_mu_user) allowed
multiuser: tmpfs open permission enforcement
  PASS: /tmp/ostest_mu_secret owner 0:0
  PASS: open(/tmp/ostest_mu_secret) denied with EACCES
  PASS: open(/tmp/ostest_mu_secret) allowed
multiuser: message queue ownership and permissions
  PASS: /var/mqueue/ostest_mu_mq owner 1000:1000
  PASS: /var/mqueue/ostest_mu_mq mode 0600
  PASS: mq_open(other user) denied errno=13
  PASS: mq_open(owner)
multiuser: named semaphore ownership and permissions
  PASS: /var/sem/ostest_mu_sem owner 1000:1000
  PASS: sem_open(other user) denied errno=13
  PASS: sem_open(owner)
multiuser: shared memory ownership and permissions
  PASS: /var/shm/ostest_mu_shm owner 1000:1000
  PASS: shm_open(other user) denied errno=13
  PASS: shm_open(owner)
multiuser: FIFO ownership and permissions
  PASS: /ostest_mu_fifo owner 1000:1000
  PASS: open fifo (other user) denied errno=13
  PASS: open fifo (owner)
multiuser: passwd lookup after credential drop
  PASS: installed /tmp/ostest_passwd
  PASS: getpwnam(root) uid=0
  PASS: getpwnam(testuser) uid=1000
multiuser_test: 0 failure(s)

[Abhishekmishra2808]

@acassis PTAL !!