Re: [PATCH] Fix readdir_r with long file names

["Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 03/01/2016 09:27 PM, Florian Weimer wrote:
> On 03/01/2016 09:14 PM, Michael Kerrisk (man-pages) wrote:
> 
>> What happens with readdir() when it gets a filename that is larger 
>> than 255 characters?
> 
> Good question.  Ugh.
> 
> readdir will return a pointer to a struct dirent whose d_name member
> will not be null-terminated, but the memory following the struct dirent
> object will contain the rest of the name, and will eventually be
> null-terminated.

So, in other words, if the caller users a declaration of the form

    struct dirent d;

(rather than say allocating a large buffer dynamically), then we have 
a buffer overrun?

Cheers,

Michael

> This will work perfectly fine if you don't copy struct dirent objects
> using memcpy, and the compiler does not optimize things too much.  We
> should implement compiler support for this wart: inhibit optimizations
> (I think there are already special cases for length-0 and length-1
> arrays at the end, so it's not totally without precedent), and warn
> about sizeof (struct dirent) and using it as a (non-pointer) declarator.
>  The second part is likely generally useful for structs whose size is
> not intended to be part of the ABI.
> 
> Florian
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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