From 0631b6beaed60ba118b0b027c0f8d35397bf5df0 Mon Sep 17 00:00:00 2001
From: Keno Fischer <keno@juliacomputing.com>
Date: Thu, 30 Sep 2021 03:51:23 -0400
Subject: [PATCH] Fix out of bounds read in slarrv

This was originally reported as https://github.com/JuliaLang/julia/issues/42415.
I've tracked this down to an our of bounds read on the following line:

https://github.com/Reference-LAPACK/lapack/blob/44ecb6a5ff821b1cbb39f8cc2166cb098e060b4d/SRC/slarrv.f#L423

In the crashing example, `M` is `0`, causing `slarrv` to read uninitialized
memory from the work array. I believe the `0` for `M` is correct and indeed,
the documentation above supports that `M` may be zero:

https://github.com/Reference-LAPACK/lapack/blob/44ecb6a5ff821b1cbb39f8cc2166cb098e060b4d/SRC/slarrv.f#L113-L116

I believe it may be sufficient to early-out this function as suggested
in this PR. However, I have limited context for the full routine here,
so I would appreciate a sanity check.
---
 SRC/clarrv.f | 2 +-
 SRC/dlarrv.f | 2 +-
 SRC/slarrv.f | 2 +-
 SRC/zlarrv.f | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/SRC/clarrv.f b/SRC/clarrv.f
index 1f09e4da6a..42f7107573 100644
--- a/SRC/clarrv.f
+++ b/SRC/clarrv.f
@@ -348,7 +348,7 @@ SUBROUTINE CLARRV( N, VL, VU, D, L, PIVMIN,
 *
 *     Quick return if possible
 *
-      IF( N.LE.0 ) THEN
+      IF( (N.LE.0).OR.(M.LE.0) ) THEN
          RETURN
       END IF
 *
diff --git a/SRC/dlarrv.f b/SRC/dlarrv.f
index b036c1e660..2994303612 100644
--- a/SRC/dlarrv.f
+++ b/SRC/dlarrv.f
@@ -350,7 +350,7 @@ SUBROUTINE DLARRV( N, VL, VU, D, L, PIVMIN,
 *
 *     Quick return if possible
 *
-      IF( N.LE.0 ) THEN
+      IF( (N.LE.0).OR.(M.LE.0) ) THEN
          RETURN
       END IF
 *
diff --git a/SRC/slarrv.f b/SRC/slarrv.f
index 9d72b339a9..95f94fd1bd 100644
--- a/SRC/slarrv.f
+++ b/SRC/slarrv.f
@@ -350,7 +350,7 @@ SUBROUTINE SLARRV( N, VL, VU, D, L, PIVMIN,
 *
 *     Quick return if possible
 *
-      IF( N.LE.0 ) THEN
+      IF( (N.LE.0).OR.(M.LE.0) ) THEN
          RETURN
       END IF
 *
diff --git a/SRC/zlarrv.f b/SRC/zlarrv.f
index 51ec558f53..e4be63e0db 100644
--- a/SRC/zlarrv.f
+++ b/SRC/zlarrv.f
@@ -348,7 +348,7 @@ SUBROUTINE ZLARRV( N, VL, VU, D, L, PIVMIN,
 *
 *     Quick return if possible
 *
-      IF( N.LE.0 ) THEN
+      IF( (N.LE.0).OR.(M.LE.0) ) THEN
          RETURN
       END IF
 *