Re: bug report: grib1 decoding, missing times results in seg fault

Hi David,
I downloaded your sample file, and found that the current version of
NCL reads it fine. I believe the problem was fixed in the development
version last January. We will be releasing a new version that will
have the fix in about a month. If you want it sooner let Mary Haley
know.
  -dave

On Dec 11, 2008, at 4:26 PM, David P. Wojtowicz wrote:

> Hi,
>
> I've noticed the following bug in NCL. (happens with 4.3.1 binary
> and self-compiled 5.0.0, both on linux)
>
> I have file containing grib1 products saved by pqact from LDM.
> For whatever reason, some of the fields are missing at some of the
> forecast times. (It seems to be a consistent problem with the
> GFS 211 files I'm saving, but could happen for any product)
>
> I have a simple NCL test script that looks like this:
>
> ----
> g=addfile("GFS-211-2008121100.grib1","r")
> print(g)
> ----
>
> This is essentially the same as ncl_filedump (and in fact
> ncl_filedump has the same problem)
>
> I get a series of warnings, noting the missing data, that look like
> this (only two copied for brevity):
>
> warning:GFS-211-2008121100.grib1->V_VEL_211_ISBL_10 is missing ft:
> 126 lv: 100
> warning:GFS-211-2008121100.grib1->V_VEL_211_ISBL_10 is missing ft:
> 126 lv: 150
>
> Then it crashes with a segmentation fault. I presume the correct
> operation is to warn about the missing data, but continue on and
> just return missing values when trying to access the missing parts
> of the data.
>
> I've debugged this and traced it to ni/src/ncl/NclGRIB.c line
> 3148. Here is the code fragment.
>
> dstep = therec->grid_dims;
> while(dstep != NULL) {
> if((dstep->dim_inq->is_gds == step->gds_type)&&
> (GdsCompare(dstep->dim_inq->gds,dstep-
> >dim_inq->gds_size,
> step->thelist->rec_inq->gds,step-
> >thelist->rec_inq->gds_size))) {
> ^^^^^^^^^^^^^^^^^^^^
> if ((step->gds_type == 203) && (dstep-
> >dim_inq->is_uv != Is_UV(step->param_number))) {
> dstep = dstep->next;
> continue;
> }
> break;
> } else {
> dstep = dstep->next;
> }
> }
>
>
> The problem is marked with ^^^^^^^^. Apparently step->thelist-
> >rec_inq goes NULL at some point before dstep does, resulting in a
> NULL reference and thus a segfault.
>
> I've temporarily solved it by adding a line "if(step->therec-
> >rec_inq == NULL) break;" just inside the while loop. However the
> code is rather complex here and I'm not sure that's the appropriate
> solution.... though it does seem to work... though I haven't tested
> all aspects of file access under this fix.
>
> If you want to reproduce it, you can grab the grib file from here:
>
> http://www.atmos.uiuc.edu/~davidw/GFS-211-2008121100.grib1
>
> running "ncl_filedump -c" on it should produce the error.
>
>
> Thanks.
>
> ----
> David Wojtowicz, Sr. Research Programmer
> IT Coordinator - School of Earth, Society and the Environment (SESE)
> University of Illinois at Urbana-Champaign
> davidw_at_uiuc.edu 217-333-8390
>
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Received on Thu Dec 11 2008 - 17:27:46 MST