Bug 248281

Description of problem:

The program below gives the error message "sh: line 0: echo: write error: Bad
file descriptor".

#include <assert.h>
#include <stdio.h>

int main(void)
{
  FILE *p1, *p2;
  int result1, result2;
  
  fclose(stdout);
  p1 = popen("echo a", "r"); assert(p1 != NULL);
  p2 = popen("echo b", "r"); assert(p2 != NULL);
  result1 = pclose(p1); result2 = pclose(p2);
  fprintf(stderr, "result1 = %d, result2 = %d\n", result1, result2);
  return 0;
}

I dug into this problem with "strace -f", and found that the stdout fd (fd 1) of
the child process p2 (pid 5072) got closed before the execve().

pipe([1, 4])                            = 0
clone(Process 5071 attached
child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0xb7f55708) = 5071
[pid  5070] close(4)                    = 0
[pid  5070] pipe([4, 5])                = 0
[pid  5070] clone(Process 5072 attached
child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0xb7f55708) = 5072
[pid  5070] close(5)                    = 0
[pid  5070] close(1)                    = 0
[pid  5070] waitpid(5071, Process 5070 suspended
 <unfinished ...>
[pid  5071] close(1 <unfinished ...>
[pid  5072] close(4 <unfinished ...>
[pid  5071] <... close resumed> )       = 0
[pid  5072] <... close resumed> )       = 0
[pid  5071] dup2(4, 1 <unfinished ...>
[pid  5072] dup2(5, 1 <unfinished ...>
[pid  5071] <... dup2 resumed> )        = 1
[pid  5072] <... dup2 resumed> )        = 1
[pid  5071] close(4 <unfinished ...>
[pid  5072] close(5 <unfinished ...>
[pid  5071] <... close resumed> )       = 0
[pid  5072] <... close resumed> )       = 0
[pid  5071] execve("/bin/sh", ["sh", "-c", "echo a"], [/* 51 vars */]
<unfinished ...>
[pid  5072] close(1 <unfinished ...>
[pid  5071] <... execve resumed> )      = 0
[pid  5072] <... close resumed> )       = 0
[pid  5072] execve("/bin/sh", ["sh", "-c", "echo b"], [/* 51 vars */]
<unfinished ...>

This seems to be caused by the following code in libc/libio/iopopen.c:

      _IO_close (parent_end);
      if (child_end != child_std_end)
        {
          _IO_dup2 (child_end, child_std_end);
          _IO_close (child_end);
        }
      /* POSIX.2:  "popen() shall ensure that any streams from previous
         popen() calls that remain open in the parent process are closed
         in the new child process." */
      for (p = proc_file_chain; p; p = p->next)
        _IO_close (_IO_fileno ((_IO_FILE *) p));

In our case, when doing the second popen(), the first popen()'s fd is 1 and it
has just been overwritten by the dup2() call, so it is wrong to close it.

Version-Release number of selected component (if applicable):

glibc-2.5-10.fc6

How reproducible:

Always

Steps to Reproduce:
1. Compile the program above and run it.
  
Actual results:

sh: line 0: echo: write error: Bad file descriptor
result1 = 0, result2 = 256

(result1 might also be 13 (SIGPIPE) if the parent pclose()'d before the child
writes its output.)

Expected results:

result1 = 0, result2 = 0

(Either or both results might also be 13.)