Question

getpwnam中是否存在内存泄漏的修复或解决方法？

Answer 1

getpwnam() 不会遭受内存泄漏。实际上，后续调用将覆盖其静态内部缓冲区。

此类函数是不可重入，因此非线程安全。 Paul建议使用getpwnam_r()这是可重入的版本，在多线程上下文中使用是安全的。

也就是说，内存泄漏是由那些通过malloc()分配内存的系统调用引起的，并且一旦返回的数据被使用，应用程序就会对free()内存负责。

在这些情况下，建议使用RAII习惯用法，以免忘记释放分配的内存 - 请参阅异常安全。 std::tr1::shared_ptr<>也是一种可行的方法：对于shared_ptr，当shared_ptr超出范围时，必须向free()原始指针提供自定义删除器。

在这种观点下，一些危险的功能是scandir()，asprintf()，vasprintf()等。

Answer 2

使用getpwnam_r。

Answer 3

我认为没有解决方法。上面的答案没有用，请参阅：

daniel@senap:~/dev/tryouts$ uname -a
Linux senap 3.2.0-24-generic #39-Ubuntu SMP Mon May 21 16:52:17 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
daniel@senap:~/dev/tryouts$ cat getpwnam-leak.c 
#include <sys/types.h>
#include <pwd.h>

extern void __libc_freeres(void);

int main()
{
  char buf[1024];
  struct passwd pw, *result;
  getpwnam_r("root", &pw, buf, sizeof(buf), &result);
  __libc_freeres();
}
daniel@senap:~/dev/tryouts$ valgrind --leak-check=full ./getpwnam-leak
==6951== Memcheck, a memory error detector
==6951== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==6951== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==6951== Command: ./getpwnam-leak
==6951== 
==6951== 
==6951== HEAP SUMMARY:
==6951==     in use at exit: 300 bytes in 11 blocks
==6951==   total heap usage: 69 allocs, 58 frees, 9,234 bytes allocated
==6951== 
==6951== 300 (60 direct, 240 indirect) bytes in 1 blocks are definitely lost in loss record 11 of 11
==6951==    at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) 
==6951==    by 0x4F35D94: nss_parse_service_list (nsswitch.c:678)
==6951==    by 0x4F36855: __nss_database_lookup (nsswitch.c:175)
==6951==    by 0x55F32A4: ???
==6951==    by 0x4EEF1AC: getpwnam_r@@GLIBC_2.2.5 (getXXbyYY_r.c:256)
==6951==    by 0x400607: main (in /home/daniel/dev/tryouts/getpwnam-leak)
==6951== 
==6951== LEAK SUMMARY:
==6951==    definitely lost: 60 bytes in 1 blocks
==6951==    indirectly lost: 240 bytes in 10 blocks
==6951==      possibly lost: 0 bytes in 0 blocks
==6951==    still reachable: 0 bytes in 0 blocks
==6951==         suppressed: 0 bytes in 0 blocks
==6951== 
==6951== For counts of detected and suppressed errors, rerun with: -v
==6951== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 2 from 2)
daniel@senap:~/dev/tryouts$

Answer 4

要解决此问题，请执行以下操作：

sudo sed -i s/compat/files/g /etc/nsswitch.conf

这似乎是由于libnss_compat中的错误引起的。有关详情，请访问bugs.debian.org。

getpwnam中是否存在内存泄漏的修复或解决方法？

4 个答案: