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File descriptor leak

From: Chris Dunlop
Subject: File descriptor leak
Date: Fri, 31 Jul 2020 14:29:59 +1000
User-agent: Mutt/1.9.4 (2018-02-28)

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

Bash is leaking a file descriptor.

if :
 while read l
   grep . /proc/$$/fdinfo/*
   pvs > /dev/null
 done < <( echo )

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

Chris Dunlop

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