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Re: Memory leak in bash 4.3

From: Jean Delvare
Subject: Re: Memory leak in bash 4.3
Date: Tue, 9 Jun 2015 21:42:50 +0200

On Tue, 9 Jun 2015 18:02:31 +0200, Jean Delvare wrote:
> I built bash 4.3.39 with --without-bash-malloc and then ran the daemon
> under valgrind for 1 minute. The back trace for the leak is:
> 3,973 bytes in 430 blocks are definitely lost in loss record 1,610 of 1,613
>    at 0x4C277AB: malloc (in 
> /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
>    by 0x471A2A: xmalloc (xmalloc.c:112)
>    by 0x461A84: array_variable_name (arrayfunc.c:917)
>    by 0x457731: parameter_brace_expand_word (subst.c:5785)
>    by 0x452DA4: param_expand (subst.c:7385)
>    by 0x4550E9: expand_word_internal (subst.c:8393)
>    by 0x4566DB: call_expand_word_internal.constprop.14 (subst.c:3299)
>    by 0x456829: expand_string_assignment (subst.c:3387)
>    by 0x4509DB: expand_string_if_necessary (subst.c:3092)
>    by 0x450E3E: do_assignment_internal (subst.c:2823)
>    by 0x45859E: expand_word_list_internal (subst.c:2912)
>    by 0x4360B7: execute_simple_command (execute_cmd.c:4000)
> I do not have a minimum test case yet, but I wanted to ask if the back
> trace above provides enough hints to recognize an already know bug and
> the commit that fixed it?

I think I have a minimal test case now:


declare -a ARRAY

FOO=${ARRAY[0]} # <-- leaks
echo $FOO

And a candidate fix:

bash 4.3: Fix memory leak in parameter_brace_expand_word

Fix a memory leak in function parameter_brace_expand_word. If
expanding an array reference and PF_ASSIGNRHS is set, function
array_variable_name is called but the allocated string is not
needed and is ignored. It must be freed before going on, otherwise
memory is leaked. Function array_variable_part does that for us
so just call it instead of function array_variable_name (as is
done in later versions of bash.)
 subst.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/subst.c
+++ b/subst.c
@@ -5782,7 +5782,7 @@ expand_arrayref:
       /* XXX - does this leak if address@hidden or name[*]? */
       if (pflags & PF_ASSIGNRHS)
-          temp = array_variable_name (name, &tt, (int *)0);
+          temp = array_variable_part (name, &tt, (int *)0);
           if (ALL_ELEMENT_SUB (tt[0]) && tt[1] == ']')
            temp = array_value (name, quoted|Q_DOUBLE_QUOTES, 0, &atype, &ind);

Jean Delvare
SUSE L3 Support

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