Bug#923422: psmisc: pstree segfault with threads (patch included)

[Charles Samuels]

Package: psmisc 
Version: 22.21-2.1+b2 
Severity: normal

Dear Maintainer,

When I run pstree on my busy servers, it usually SIGSEGVs before outputting
anything.

This is because pstree is calling `fclose(f)` on an `f` that may 
be null, which is not permitted:

       The behaviour of fclose() is undefined if the stream parameter is
       an illegal pointer, or is  a  descriptor  already
       passed to a previous invocation of fclose().

(quoting man fclose)

-- System Information:
Debian Release: 9.7
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.9.0-8-amd64 (SMP w/64 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), 
LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages psmisc depends on:
ii  libc6        2.24-11+deb9u3
ii  libselinux1  2.6-3+b3
ii  libtinfo5    6.0+20161126-1+deb9u2

psmisc recommends no packages.

psmisc suggests no packages.

-- no debconf information
diff -ur psmisc-22.21/src/pstree.c psmisc-22.21-fixed/src/pstree.c
--- psmisc-22.21/src/pstree.c	2014-02-02 05:59:07.000000000 +0000
+++ psmisc-22.21-fixed/src/pstree.c	2019-02-27 23:19:40.611866628 +0000
@@ -819,7 +819,9 @@
     }
     /* Fall back to old method */
     sprintf(threadname, "{%.*s}", COMM_LEN, comm);
-    fclose(file);
+    if (file) { 
+        fclose(file);
+    }
     return threadname;
 }