Fix stack overflow due to too deep recursion

Bug: 45713

How to reproduce:
Run this command inside screen
$ printf '\x1b[10000000T'

screen will recursively call MScrollV to depth n/256. This is time consuming and will overflow stack if n is huge.

1 files changed, 7 insertions, 7 deletions

diff --git a/src/ansi.c b/src/ansi.c
index a342fb1..152d2ef 100644
--- a/src/ansi.c
+++ b/src/ansi.c
@@ -2502,13 +2502,13 @@ int n, ys, ye, bce;
     return;
   if (n > 0)
     {
+      if (ye - ys + 1 < n)
+	n = ye - ys + 1;
       if (n > 256)
 	{
 	  MScrollV(p, n - 256, ys, ye, bce);
 	  n = 256;
 	}
-      if (ye - ys + 1 < n)
-	n = ye - ys + 1;
 #ifdef COPY_PASTE
       if (compacthist)
 	{
@@ -2562,14 +2562,14 @@ int n, ys, ye, bce;
     }
   else
     {
-      if (n < -256)
-	{
-	  MScrollV(p, n + 256, ys, ye, bce);
-	  n = -256;
-	}
       n = -n;
       if (ye - ys + 1 < n)
 	n = ye - ys + 1;
+      if (n > 256)
+	{
+	  MScrollV(p, - (n - 256), ys, ye, bce);
+	  n = 256;
+	}
 
       ml = p->w_mlines + ye;
       /* Clear lines */