to_char(): prevent accesses beyond the allocated buffer

Previously very long field masks for floats could access memory
beyond the existing buffer allocated to hold the result.

Reported by Andres Freund and Peter Geoghegan.	Backpatch to all
supported versions.

Security: CVE-2015-0241

1 files changed, 3 insertions, 1 deletions

diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index e17bea26615..6d4cd1feade 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -4416,7 +4416,9 @@ NUM_numpart_to_char(NUMProc *Np, int id)
 					Np->num_in = TRUE;
 				}
 			}
-			++Np->number_p;
+			/* do no exceed string length */
+			if (*Np->number_p)
+				++Np->number_p;
 		}
 
 		end = Np->num_count + (Np->out_pre_spaces ? 1 : 0) + (IS_DECIMAL(Np->Num) ? 1 : 0);