Re: obscure bug "extern void free (void *__ptr) __attribute__ ((__nothrow__ , __leaf__));"

[Mathias Steiger]

Thanks for your reply. My report maybe did contain a lot of too tightly 
packed information. I try to clarify:

The git repository is the official one of Libreelec (a Linux 
distribution). Naturally it has to download packages.

I did in fact quote an brief excerpt of the wrongfully inserted line two 
times (with context where it is inserted). I made that clear by 
indentation, a colon and also the context. When I was speaking of a 
"diff" command inserting it's output somewhere else, you can see that I 
did in fact quote "diff" formatted output afterwards as marked. It might 
be confusing, because it might look a bit like I was using "diff" to 
quote the inserted line instead.

When I was speaking of removing "the line", I was referring to the only 
line I explicitly mentioned by line number and also the only line 
mentioned that has a corresponding "if" statement. It is of course hard 
to follow this, if you do not open and look at the mentioned file at the 
same time.

By "silenced command output" I was simply referring to what is happening 
in "the line", i.e. a command having its output directed at >& /dev/null.

I don't understand the rest of the paragraph you wrote.

In my mind, I have found an impossible execution: a "silenced command" 
outputs to a file it shouldn't output into.

My knowledge of bash is not perfect, but I don't believe this should or 
can ever happen. Unless of course you wrote another script to 
specifically remove the redirection to /dev/null and then you executed 
that altered script.

How would it only "appear to be silenced"? Can you somehow resurrect 
output directed at /dev/null? I guess anything is possible if you made a 
lot of effort to do it, but this doesn't seem likely to me in an 
Autoconfig script. Especially considering the insertion is so random and 
it doesn't happen with previous bash versions.

From what I can tell, there is no further need to dissect the rest of 
the script to know that this is a bug in bash, because realistically 
this can never make sense as it is.

In my limited knowledge, it looks to me like some pointer address 
overflowed - due to the length and complexity of the script - and then 
it just reads from some arbitrary old buffer.


On 1/21/21 10:27 PM, Mathias Steiger wrote:
>     {if echo "27ac5e2f757302" >& /dev/null; then echo "yes"; else echo 
> "no"; fi } > output
>
> and then the file "output" would contain:
>
>     "extern void free (void *__ptr) __attribute__ ((__nothrow__ , 
> __leaf__)); 27ac5e2f757302 yes"
>
> This is more or less what is happening here.