log_formatted: Fill the log buffer with nuls to make sure we cannot

accidentally leave the string unterminated.

diff --git a/log.c b/log.c
index f36b105..045f031 100644 (file)
--- a/log.c
+++ b/log.c
@@ -409,6 +409,12 @@ static void log_formatted(enum logcode code,
        extern int am_daemon;
        int64 b;
 
+       /* We expand % codes one by one in place in buf.  We don't
+        * copy in the terminating nul of the inserted strings, but
+        * rather keep going until we reach the nul of the format.
+        * Just to make sure we don't clobber that nul and therefore
+        * accidentally keep going, we zero the buffer now. */
+       memset(buf, 0, sizeof buf);
        strlcpy(buf, format, sizeof(buf));
        
        for (s=&buf[0]; 
@@ -466,7 +472,11 @@ static void log_formatted(enum logcode code,
                        break;
                }
 
-               if (!n) continue;
+               /* n is the string to be inserted in place of this %
+                * code; l is its length not including the trailing
+                * NUL */
+               if (!n)
+                       continue;
 
                l = strlen(n);
 
@@ -476,11 +486,16 @@ static void log_formatted(enum logcode code,
                        exit_cleanup(RERR_MESSAGEIO);
                }
 
+               /* Shuffle the rest of the string along to make space for n */
                if (l != 2) {
                        memmove(s+(l-1), s+1, strlen(s+1)+1);
                }
+
+               /* Copy in n but NOT its nul, because the format sting
+                * probably continues after this. */
                memcpy(p, n, l);
 
+               /* Skip over inserted string; continue looking */
                s = p+l;
        }