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Re: Fwd: [PATCH] Don't allow attackers to inject arbitrary data into stack through LD_DEBUG

On Mon, Aug 10, 2015 at 10:49 AM, Andreas Schwab <> wrote:
> Alex <> writes:
>> On Mon, Aug 10, 2015 at 1:01 AM, Andreas Schwab <> wrote:
>>> Alex Dowad <> writes:
>>>> diff --git a/elf/rtld.c b/elf/rtld.c
>>>> index 6dcbabc..ee194a6 100644
>>>> --- a/elf/rtld.c
>>>> +++ b/elf/rtld.c
>>>> @@ -2408,6 +2408,8 @@ process_dl_debug (const char *dl_debug)
>>>>             char *copy = strndupa (dl_debug, len);
>>>>             _dl_error_printf ("\
>>>>  warning: debug option `%s' unknown; try LD_DEBUG=help\n", copy);
>>> Use %.*s instead.
>> Thanks for your reply. That would help to avoid potentially voluminous
>> output to the console, but doesn't fix the (potential) security hole
>> of copying an arbitrary, attacker-supplied string onto the stack.
> You don't need the copy any more.

Andreas, I'm a bit slow here so please help me out: why is the copy
needed *even if* printf("%s", ...) is used? I've been trying to figure
out why the original author used strndupa in the first place but
haven't wrapped my mind around it yet.

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