macos 10 setuid无故失败

我运行此代码是为了在以下情况下更改实际uid：

#include <cstdlib>
#include <cstdio>
#include <errno.h>
#include <sys/types.h>
#include <unistd.h>

void printstat()
{
    printf("uid: %d, euid: %d\n",getuid(),geteuid());
}

int main(int argc, char** argv)
{
    if (argc < 2)
    {
            return -1;
    }
    int m_targetUid = atoi(argv[1]);
    printstat();
    uid_t realUID = getuid();
    printf("Setting effective uid to %d\n",m_targetUid);
    seteuid(m_targetUid);
    printstat();
    if (m_targetUid != realUID)
    {
            printf("Setting real uid to %d\n",m_targetUid);
            int res = setuid(m_targetUid);
            printf("setuid(%d) returned: %d\n",m_targetUid,res);
            if (0 > setuid(m_targetUid))
            {
                    printf("setuid(%d) failed: %d, getuid() returned %d, geteuid returned %d\n",m_targetUid,errno,realUID,geteuid());
                    exit(-1);
            }
    }
}

这是我以root用户身份运行时的输出：

nnlnb-mm-041: root# /tmp/setuidBug 70
uid: 0, euid: 0
Setting effective uid to 70
uid: 0, euid: 70
Setting real uid to 70
setuid(70) returned: -1
setuid(70) failed: 1, getuid() returned 0, geteuid returned 70

---

我终于设法解决了这个问题，显然在macos中，您必须将有效uid设置回root，它才能工作。代码如下

#include <cstdlib>
#include <cstdio>
#include <errno.h>
#include <sys/types.h>
#include <unistd.h>

void printstat()
{
    printf("uid: %d, euid: %d\n",getuid(),geteuid());
}

int main(int argc, char** argv)
{
    if (argc < 2)
    {
            return -1;
    }
    int m_targetUid = atoi(argv[1]);
    printstat();
    uid_t realUID = getuid();
    printf("Setting effective uid to %d\n",m_targetUid);
    seteuid(m_targetUid);
    printstat();
    printf("Setting effective uid to 0\n");
    seteuid(0);
    printstat();
    if (m_targetUid != realUID)
    {
            printf("Setting real uid to %d\n",m_targetUid);
            int res = setuid(m_targetUid);
            printf("setuid(%d) returned: %d\n",m_targetUid,res);
            if (0 > setuid(m_targetUid))
            {
                    printf("setuid(%d) failed: %d, getuid() returned %d, geteuid returned     %d\n",m_targetUid,errno,realUID,geteuid());
                    exit(-1);
            }
    }
    printstat();
}

---

之后我设法自己解决了这个问题。事实证明，必须将euid更改回0，setuid才能工作。将使用有效的代码编辑帖子。不要将答案编辑为问题。如果你愿意，你可以发布你自己的答案。

#include <cstdlib>
#include <cstdio>
#include <errno.h>
#include <sys/types.h>
#include <unistd.h>

void printstat()
{
    printf("uid: %d, euid: %d\n",getuid(),geteuid());
}

int main(int argc, char** argv)
{
    if (argc < 2)
    {
            return -1;
    }
    int m_targetUid = atoi(argv[1]);
    printstat();
    uid_t realUID = getuid();
    printf("Setting effective uid to %d\n",m_targetUid);
    seteuid(m_targetUid);
    printstat();
    printf("Setting effective uid to 0\n");
    seteuid(0);
    printstat();
    if (m_targetUid != realUID)
    {
            printf("Setting real uid to %d\n",m_targetUid);
            int res = setuid(m_targetUid);
            printf("setuid(%d) returned: %d\n",m_targetUid,res);
            if (0 > setuid(m_targetUid))
            {
                    printf("setuid(%d) failed: %d, getuid() returned %d, geteuid returned     %d\n",m_targetUid,errno,realUID,geteuid());
                    exit(-1);
            }
    }
    printstat();
}

    uid: 0, euid: 0
    Setting effective uid to 70
    uid: 0, euid: 70
    Setting effective uid to 0
    uid: 0, euid: 0
    Setting real uid to 70
    setuid(70) returned: 0
    uid: 70, euid: 70