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File descriptor leak

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From: chris@onthe.net.au
To: bug-bash@gnu.org
Subject: File descriptor leak

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -g -O2 -fdebug-prefix-map=/build/bash-2bxm7h/bash-5.0=. -fstack-protector-strong -Wformat -Werror=format-security -Wall -Wno-parentheses -Wno-format-security
uname output: Linux b2 5.7.9-otn-00003-g8c0bb49bc11c #1 SMP Fri Jul 17 04:37:20 UTC 2020 x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 5.0
Patch Level: 3
Release Status: release

Description:
Bash is leaking a file descriptor.

Repeat-By:
----------------------------------------------------------------------
#!/bin/bash
if :
then
  while read l
  do
    grep . /proc/$$/fdinfo/*
    pvs > /dev/null
  done < <( echo )
  echo
fi
----------------------------------------------------------------------

The script generates output like:

/proc/2320431/fdinfo/0:pos:     0
/proc/2320431/fdinfo/0:flags:   0100000
/proc/2320431/fdinfo/0:mnt_id:  10
/proc/2320431/fdinfo/1:pos:     0
/proc/2320431/fdinfo/1:flags:   02
/proc/2320431/fdinfo/1:mnt_id:  20
/proc/2320431/fdinfo/10:pos:    0
/proc/2320431/fdinfo/10:flags:  02000002
/proc/2320431/fdinfo/10:mnt_id: 20
/proc/2320431/fdinfo/2:pos:     0
/proc/2320431/fdinfo/2:flags:   02
/proc/2320431/fdinfo/2:mnt_id:  20
/proc/2320431/fdinfo/255:pos:   123
/proc/2320431/fdinfo/255:flags: 02100000
/proc/2320431/fdinfo/255:mnt_id:        22
grep: /proc/2320431/fdinfo/3: No such file or directory
/proc/2320431/fdinfo/63:pos:    0
/proc/2320431/fdinfo/63:flags:  00
/proc/2320431/fdinfo/63:mnt_id: 10
File descriptor 63 (pipe:[189620647]) leaked on pvs invocation. Parent PID 2320431: /bin/bash

The last 'echo' within the 'if' is required to trigger the error.

The 'grep' is just to see the open file descriptors at that point, it's 
not required to trigger the bug.

The 'pvs' (part of the lvm2 Logical Volume Manager suite) is also not 
required to trigger the bug, it's just how I noticed the bug. The lvm2 
stuff is particularly loud about file descriptor leaks.

Oh. Huh. I just noticed this also reproduces the problem:
----------------------------------------------------------------------
# pvs < <(echo) > /dev/null
File descriptor 63 (pipe:[190051752]) leaked on pvs invocation. Parent PID 204155: -bash
----------------------------------------------------------------------

This version of the problem may be subtly different because as previously 
noted the first reproducer script requires the 'echo' within the 'if'.

See also:
- https://lists.gnu.org/archive/html/bug-bash/2017-01/msg00026.html
- https://github.com/lvmteam/lvm2/blob/e10f20bc23088a2f9f7529f8f2b40d9c1fcb54c6/tools/lvmcmdline.c#L3333

-- 
Chris Dunlop

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File descriptor leak Chris Dunlop <chris@onthe.net.au> - 2020-07-31 14:29 +1000

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