Bash、用 CLOEXEC 分叉

Bash、用 CLOEXEC 分叉

Bash 可以在执行子进程的同时防止子进程继承文件描述符吗?

if flock -nx 9
then
  # If begin program runs away, it will keep the lock.
  begin program
else
  echo "Lock held :/)" >&2
fi 9> /tmp/lk

答案1

据我所知,没有。您必须手动关闭它:

if flock 9 -nx
then
   program 9>&- #<= manual close of fd 9 after `program` has forked but before it execs
else
  echo "Lock held :/)" >&2
fi 9> /tmp/lk

fcntl如果你想获得额外的 hacky,你可以通过直接调用该函数来设置标志ctypes.sh:

#!/bin/bash

echo initial
ls /proc/$$/fd/

echo with 9
{

ls /proc/$$/fd/

echo with 9 in an execced child
bash -c ' ls /proc/$$/fd/'

} 9</etc/passwd


echo
echo BEGIN MAGIC
FD_CLOEXEC=1
FD_SETFD=2

. ctypes.sh
echo initial
ls /proc/$$/fd/

echo with 9
{

dlcall fcntl int:9 int:$FD_SETFD int:$FD_CLOEXEC

ls /proc/$$/fd/

echo with 9 in an execced child
bash -c ' ls /proc/$$/fd/'

} 9</etc/passwd

输出:

initial
0
1
2
255
with 9
0
1
2
255
9
with 9 in an execced child
0
1
2
3
9

BEGIN MAGIC
initial
0
1
2
255
with 9
0
1
2
255
9
with 9 in an execced child
0
1
2
3

(不是粘贴错误——当子bash被执行时,9确实被关闭了)。

答案2

使用 bash 5.0+ 和示例可加载模块(debian 要求您还安装该bash-builtins软件包),您可以使用 fdflags 可加载模块。

if flock -nx 9
then
  enable -f /usr/lib/bash/fdflags fdflags
  fdflags -s+cloexec 9
  begin program
else
  echo "Lock held :/)" >&2
fi 9> /tmp/lk

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