Kernel/LibC: Implement setreuid

Kernel/API/Syscall.h

@@ -79,6 +79,7 @@ namespace Kernel {
     S(setegid)                \
     S(setuid)                 \
     S(setgid)                 \
+    S(setreuid)               \
     S(setresuid)              \
     S(setresgid)              \
     S(alarm)                  \

Kernel/Process.h

@@ -324,6 +324,7 @@ public:
     KResultOr<int> sys$setegid(gid_t);
     KResultOr<int> sys$setuid(uid_t);
     KResultOr<int> sys$setgid(gid_t);
+    KResultOr<int> sys$setreuid(uid_t, uid_t);
     KResultOr<int> sys$setresuid(uid_t, uid_t, uid_t);
     KResultOr<int> sys$setresgid(gid_t, gid_t, gid_t);
     KResultOr<unsigned> sys$alarm(unsigned seconds);

Kernel/Syscalls/setuid.cpp

@@ -73,6 +73,31 @@ KResultOr<int> Process::sys$setgid(gid_t new_gid)
     return 0;
 }
 
+KResultOr<int> Process::sys$setreuid(uid_t new_ruid, uid_t new_euid)
+{
+    REQUIRE_PROMISE(id);
+
+    if (new_ruid == (uid_t)-1)
+        new_ruid = uid();
+    if (new_euid == (uid_t)-1)
+        new_euid = euid();
+
+    auto ok = [this](uid_t id) { return id == uid() || id == euid() || id == suid(); };
+    if (!ok(new_ruid) || !ok(new_euid))
+        return EPERM;
+
+    if (new_ruid < (uid_t)-1 || new_euid < (uid_t)-1)
+        return EINVAL;
+
+    if (euid() != new_euid)
+        set_dumpable(false);
+
+    ProtectedDataMutationScope scope { *this };
+    m_uid = new_ruid;
+    m_euid = new_euid;
+    return 0;
+}
+
 KResultOr<int> Process::sys$setresuid(uid_t new_ruid, uid_t new_euid, uid_t new_suid)
 {
     REQUIRE_PROMISE(id);

Userland/Libraries/LibC/unistd.cpp

@@ -555,6 +555,12 @@ int setgid(gid_t gid)
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
+int setreuid(uid_t ruid, uid_t euid)
+{
+    int rc = syscall(SC_setreuid, ruid, euid);
+    __RETURN_WITH_ERRNO(rc, rc, -1);
+}
+
 int setresuid(uid_t ruid, uid_t euid, uid_t suid)
 {
     int rc = syscall(SC_setresuid, ruid, euid, suid);

Userland/Libraries/LibC/unistd.h

@@ -74,6 +74,7 @@ int seteuid(uid_t);
 int setegid(gid_t);
 int setuid(uid_t);
 int setgid(gid_t);
+int setreuid(uid_t, uid_t);
 int setresuid(uid_t, uid_t, uid_t);
 int setresgid(gid_t, gid_t, gid_t);
 pid_t tcgetpgrp(int fd);