[groff] 15/17: [libgroff]: Clear string storage before using it.

[G. Branden Robinson]

gbranden pushed a commit to branch master
in repository groff.

commit 6f3a812c03728bca15faaec3466b241c1beb0464
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
AuthorDate: Sat Feb 17 18:25:27 2024 -0600

    [libgroff]: Clear string storage before using it.
    
    * src/libs/libgroff/string.cpp (string::string): When constructing a new
      string from a pointer to char, if the pointed-to-string doesn't
      exactly fit the storage reserved for it, populate the storage with
      nulls bytes before copying, to avoid reads of garbage heap memory.
    
    While debugging, I was seeing stuff like this and it worried me.
    
    grops:<standard input>:4: debug: GBR: created new font resource 
'ZapfDingbats-ReversemU'
    grops:<standard input>:4: debug: GBR: created new font resource 
'Symbol-Slanted'
    grops:<standard input>:4: debug: GBR: created new font resource 
'FreeEuro�뭨�'
    
    grops:<standard input>:4: debug: GBR: created new font resource 
'Symbol-Slanted'
    grops:<standard input>:4: debug: GBR: created new font resource 
'ZapfDingbats-Reverse'
    grops:<standard input>:4: debug: GBR: created new font resource 
'FreeEuro�kJø¿½Ž'
    
    grops:<standard input>:4: debug: GBR: created new font resource 
'Symbol-Slanted'
    grops:<standard input>:4: debug: GBR: created new font resource 
'ZapfDingbats-Reverse'
    grops:<standard input>:4: debug: GBR: created new font resource 
'FreeEuro�kա'
    
    grops:<standard input>:4: debug: GBR: created new font resource 
'Symbol-Slanted'
    grops:<standard input>:4: debug: GBR: created new font resource 
'ZapfDingbats-Reverse'
    grops:<standard input>:4: debug: GBR: created new font resource 
'FreeEuro�KH�q'
    
    As shown, the garbage bytes change with each run of grops.
    
    It seems like sooner or later, something bad will come of that.
    
    Now, the same messages look like this, consistently:
    
    grops:<standard input>:4: debug: GBR: created new font resource 
'ZapfDingbats-Reverse'
    grops:<standard input>:4: debug: GBR: created new font resource 
'Symbol-Slanted'
    grops:<standard input>:4: debug: GBR: created new font resource 'FreeEuro'
---
 ChangeLog                    | 8 ++++++++
 src/libs/libgroff/string.cpp | 2 ++
 2 files changed, 10 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 8891546ea..ca1390983 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2024-02-17  G. Branden Robinson <g.branden.robinson@gmail.com>
+
+       * src/libs/libgroff/string.cpp (string::string): When
+       constructing a new string from a pointer to char, if the
+       pointed-to-string doesn't exactly fit the storage reserved for
+       it, populate the storage with nulls bytes before copying, to
+       avoid reads of garbage heap memory.
+
 2024-02-17  G. Branden Robinson <g.branden.robinson@gmail.com>
 
        * src/devices/grops/psrm.cpp (resource::resource): Spell "file
diff --git a/src/libs/libgroff/string.cpp b/src/libs/libgroff/string.cpp
index 0633db526..b62e131bb 100644
--- a/src/libs/libgroff/string.cpp
+++ b/src/libs/libgroff/string.cpp
@@ -103,6 +103,8 @@ string::string(const char *p)
   else {
     len = strlen(p);
     ptr = salloc(len, &sz);
+    if (len < sz)
+      memset(ptr, 0, sz);
     if (len != 0)
       memcpy(ptr, p, len);
   }