fix carry into uninitialized slots during printf floating point rounding

in cases where rounding caused a carry, the slot into which the carry
was taking place was unconditionally treated as valid, despite the
possibility that it could be a new slot prior to the beginning of the
existing non-rounded number. in theory this could lead to unbounded
runaway carry, but in order for that to happen, the whole
uninitialized buffer would need to have been pre-filled with 32-bit
integer values greater than or equal to 999999999.

patch based on proposed fix by Morten Welinder, who also discovered
and reported the bug.

diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c
index 31c3d5d..bec63ec 100644 (file)
--- a/src/stdio/vfprintf.c
+++ b/src/stdio/vfprintf.c
@@ -356,9 +356,9 @@ static int fmt_fp(FILE *f, long double y, int w, int p, int fl, int t)
                                *d = *d + i;
                                while (*d > 999999999) {
                                        *d--=0;
+                                       if (d<a) *--a=0;
                                        (*d)++;
                                }
-                               if (d<a) a=d;
                                for (i=10, e=9*(r-a); *a>=i; i*=10, e++);
                        }
                }