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utils: Directly use syscall() to close open FDs in closefrom() 

This avoids any allocations, since calling malloc() after fork() is
potentially unsafe.

Fixes #990.
This commit is contained in:
Tobias Brunner 2015-06-11 12:19:56 +02:00
parent b410d7f8ff
commit f25f4192c7
2 changed files with 55 additions and 7 deletions
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2
configure.ac
View File

@ -591,7 +591,7 @@ AC_CHECK_FUNC([syslog], [
])
AM_CONDITIONAL(USE_SYSLOG, [test "x$syslog" = xtrue])
AC_CHECK_HEADERS(sys/sockio.h glob.h net/if_tun.h)
AC_CHECK_HEADERS(sys/sockio.h sys/syscall.h glob.h net/if_tun.h)
AC_CHECK_HEADERS(net/pfkeyv2.h netipsec/ipsec.h netinet6/ipsec.h linux/udp.h)
AC_CHECK_HEADERS([netinet/ip6.h linux/fib_rules.h], [], [],
[

60
src/libstrongswan/utils/utils.c
View File

@ -25,7 +25,22 @@
#endif
#ifndef HAVE_CLOSEFROM
#if defined(__linux__) && defined(HAVE_SYS_SYSCALL_H)
# include <sys/stat.h>
# include <fcntl.h>
# include <sys/syscall.h>
/* This is from the kernel sources. We limit the length of directory names to
* 256 as we only use it to enumerate FDs. */
struct linux_dirent64 {
u_int64_t d_ino;
int64_t d_off;
unsigned short d_reclen;
unsigned char d_type;
char d_name[256];
};
#else /* !defined(__linux__) || !defined(HAVE_SYS_SYSCALL_H) */
# include <dirent.h>
#endif /* defined(__linux__) && defined(HAVE_SYS_SYSCALL_H) */
#endif
#include <library.h>
@ -120,14 +135,46 @@ void wait_sigint()
*/
void closefrom(int low_fd)
{
DIR *dir;
struct dirent *entry;
int max_fd, dir_fd, fd;
/* try to close only open file descriptors on Linux... This is potentially
* unsafe when called after fork() in multi-threaded applications. In
* particular opendir() will require an allocation. So it depends on how
* the malloc() implementation handles such situations */
/* try to close only open file descriptors on Linux... */
#if defined(__linux__) && defined(HAVE_SYS_SYSCALL_H)
/* By directly using a syscall we avoid any calls that might be unsafe after
* fork() (e.g. malloc()). */
char buffer[sizeof(struct linux_dirent64)];
struct linux_dirent64 *entry;
int offset, len;
dir_fd = open("/proc/self/fd", O_RDONLY);
if (dir_fd != -1)
{
while ((len = syscall(SYS_getdents64, dir_fd, buffer,
sizeof(buffer))) > 0)
{
for (offset = 0; offset < len; offset += entry->d_reclen)
{
entry = (struct linux_dirent64*)(buffer + offset);
if (!isdigit(entry->d_name[0]))
{
continue;
}
fd = atoi(entry->d_name);
if (fd != dir_fd && fd >= low_fd)
{
close(fd);
}
}
}
close(dir_fd);
return;
}
#else /* !defined(__linux__) || !defined(HAVE_SYS_SYSCALL_H) */
/* This is potentially unsafe when called after fork() in multi-threaded
* applications. In particular opendir() will require an allocation.
* Depends on how the malloc() implementation handles such situations. */
DIR *dir;
struct dirent *entry;
dir = opendir(FD_DIR);
if (dir)
{
@ -147,6 +194,7 @@ void closefrom(int low_fd)
closedir(dir);
return;
}
#endif /* defined(__linux__) && defined(HAVE_SYS_SYSCALL_H) */
/* ...fall back to closing all fds otherwise */
#ifdef WIN32