[LTP] [PATCH v4 13/13] Add statmount07 test

[Jan Kara]

Hi!

On Fri 04-10-24 11:17:21, Cyril Hrubis wrote:
> > That seems to be a valid value, since I get PASS. Kernel bug?
> 
> Looking at kernel it's a bit confusing, the bufsize is supposed to be
> the size of the structure plus the buffer allocated for the string
> reply. Which makes the code more complicated than it could have been if
> these two were separeted properly.
> 
> 
> However we do have:
> 
>        if (kbufsize >= s->bufsize)
>                 return -EOVERFLOW;
> 
> in statmount_string(), so we will trigger the error there if we pass one
> of the requests that is supposed to produce a string reply.

Yes, if STATMOUNT_STRING_REQ is set, the above check should always make
sure bufsize is large enough.

> But there seems to be something strange going on in the
> prepare_kstatmount() as well, we do have:
> 
>         if (ks->mask & STATMOUNT_STRING_REQ) {
>                 if (bufsize == sizeof(ks->sm))
>                         return -EOVERFLOW;
> 
> 		^ This line should probably be if (bufsize <= sizeof(ks->sm))
>                   because we are trying to make sure that the structure is large
> 		  enough that we can write at the offset where the
> 		  string area starts.
> 
> 		  It seems to be guarded by the checks in
> 		  statmount_string() later on as well, so I suppose that we
> 		  will trigger the EOVERFLOW slightly later if this does not
> 		  work though. CCying Jan to have a look.

Yup, this looks confusing to me as well. Christian, is this check indeed
meant to bail early if the buffer obviously is not large enough? Shouldn't
it then be <= as Cyril suggests? I have a feeling I might be missing some
"extensible syscall" magic that does the check bufsize < sizeof(struct)
automatically somewhere but I could not find it...

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR