From 78f5466b4fc5b763eca98568ce83ecc9a1249cf5 Mon Sep 17 00:00:00 2001
From: Nikolai Kondrashov <spbnick@gmail.com>
Date: Mon, 12 Feb 2018 20:20:15 +0200
Subject: [PATCH] Do not unset local array variable in Bash func

Do not unset local array variable to clear it in "get_module_verinfo"
function in "dkms" script. Assign empty array instead.

When a local variable is "unset" in Bash, it is completely removed, and
its scope is lost. If a new value is assigned to the same name
afterwards (and there was no local variable with the same name up the
stack), a new variable is created, this time with the global scope.

If then a local variable is created with the same name again, it hides
the global one, and if that is "unset" again, the global one becomes
visible again.

This is what happens with the "check_version_sanity" and
"get_module_verinfo" functions in "dkms" script. It works OK, if both
kernel and installed module have version info, but when there is more
than one module to process, and a second or later in-kernel module
("$kernels_module") lacks any version info in the kernel, the
"check_version_sanity" function uses the last built module's version
info instead.

I.e. this is how "check_version_sanity" would work for a module with
version information in both kernel and dkms build:

    # Unset local "res", assign version info to global "res"
    get_module_verinfo $kernels_module; kernels_info=("${res[@]}")
    # Unset global "res", assign version info to global "res"
    get_module_verinfo $dkms_module; dkms_info=("${res[@]}")

This is how "check_version_sanity" would work for a module without
version information in the kernel, but with version information in the
module being installed

    # Unset local "res", do not assign anything
    get_module_verinfo $kernels_module; kernels_info=("${res[@]}")
    # Unset global "res", if any, assign version info to global "res"
    get_module_verinfo $dkms_module; dkms_info=("${res[@]}")

And for a second invocation of "check_version_sanity" for a similar
module:

    # Unset local "res", do not assign anything
    # This uses the value of global "res" assigned last time
    get_module_verinfo $kernels_module; kernels_info=("${res[@]}")
    # Unset global "res", assign result to global "res"
    get_module_verinfo $dkms_module; dkms_info=("${res[@]}")
---
 dkms | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dkms b/dkms
index 5a9bb29b..b5b792de 100644
--- a/dkms
+++ b/dkms
@@ -742,7 +742,7 @@ read_conf()
 
 # Little helper function for parsing the output of modinfo.
 get_module_verinfo(){
-    unset res
+    res=()
     local vals=
     while read -a vals; do
     case ${vals[0]} in