[Bug] i.cca causes segmentation fault due to incorrect indexing

[jayneel-shah18]

Describe the bug

The i.cca module crashes with a segmentation fault (exit code -11) when run with valid signature and group inputs. This is caused by off-by-one indexing errors in the C source code: arrays allocated with size n are accessed using 1-based indexing (1..n), instead of the correct 0-based indexing (0..n-1), leading to invalid memory access.

To reproduce

1. Set region with sufficient size

g.region n=20 s=0 e=20 w=0 rows=200 cols=200

2. Generate input rasters and a training map with at least 3 classes.

r.mapcalc expression="band1 = 50 + 30 * sin(row() / 20.0) + 20 * cos(col() / 15.0)"
r.mapcalc expression="band2 = 40 + 25 * exp(-(((row() - 100)^2 + (col() - 100)^2) / 2000.0))"
r.mapcalc expression="band3 = 30 + (row() + col()) / 10.0"
r.mapcalc "cca_training = if(row() < 60 && col() < 60, 1, \
                   if(row() >= 60 && row() < 140 && col() >= 60 && col() < 140, 2, \
                   if(row() >= 140 && col() >= 140, 3, null())))"

3. Create an imagery group and subgroup with 3 raster bands.

i.group group=cca_group subgroup=cca_subgroup input=band1,band2,band3

4. Generate a signature file using i.gensig.

i.gensig trainingmap=cca_training group=cca_group subgroup=cca_subgroup signaturefile=cca_sig

5. Run i.cca with the generated group, subgroup, and signature file:

   i.cca group=cca_group subgroup=cca_subgroup signature=cca_sig output=cca_output

6. Observe a segmentation fault (crash).

Expected behavior

The module should successfully compute canonical components and write output rasters, as long as valid inputs and signatures are provided.

Screenshots

System description

• Operating System: Windows Subsystem for Linux (WSL)
• GRASS GIS version: 8.4
• details about further software components
  • GRASS 8.5.0dev
  • Python verison: 3.10.12
  • wxPython version: 4.2.2

Possible Solution

After debugging, I found out that the core issue lies in main.c of i.cca, where vectors and matrices (e.g., mu, cov, nsamp) are allocated for nclass or bands, but loop indices start from 1 to n, exceeding bounds. This causes invalid memory writes and reads, leading to segmentation faults on inputs.

The fix is implemented in #5948, which closes this issue.