[PATCH] ar: Fix GCC7 -Wformat-length issues.

[Mark Wielaard <mjw at redhat dot com>]

GCC7 adds warnings for snprintf formatting into too small buffers.
Fix the two issues pointed out by the new warning. The ar header
fields are fixed length containing left-justified strings without
zero terminator. snprintf always adds a '\0' char at the end (which
we then don't copy into the ar header field) and numbers are decimal
strings of fixed 10 chars  (-Wformat-length thinks formatting
them as size_t might overflow on 64bit arches).

Signed-off-by: Mark Wielaard <mjw@redhat.com>
---
 src/ChangeLog |  7 +++++++
 src/ar.c      | 15 +++++++++++----
 src/arlib.c   | 10 +++++++---
 3 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/src/ChangeLog b/src/ChangeLog
index b2909b6..3314706 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,10 @@
+2016-11-10  Mark Wielaard  <mjw@redhat.com>
+
+	* ar.c (write_member): Make sure tmpbuf is large enough to contain
+	a starting '/' and ending '\0' char.
+	(do_oper_insert): Likewise.
+	* arlib.c (arlib_finalize): Format tmpbuf as PRId32 decimal.
+
 2016-11-02  Mark Wielaard  <mjw@redhat.com>
 
 	* addr2line.c (handle_address): Add fallthrough comment.
diff --git a/src/ar.c b/src/ar.c
index 1320d07..f2160d3 100644
--- a/src/ar.c
+++ b/src/ar.c
@@ -1,5 +1,5 @@
 /* Create, modify, and extract from archives.
-   Copyright (C) 2005-2012 Red Hat, Inc.
+   Copyright (C) 2005-2012, 2016 Red Hat, Inc.
    This file is part of elfutils.
    Written by Ulrich Drepper <drepper@redhat.com>, 2005.
 
@@ -853,7 +853,10 @@ write_member (struct armem *memb, off_t *startp, off_t *lenp, Elf *elf,
 	      off_t end_off, int newfd)
 {
   struct ar_hdr arhdr;
-  char tmpbuf[sizeof (arhdr.ar_name) + 1];
+  /* The ar_name is not actually zero teminated, but we need that for
+     snprintf.  Also if the name is too long, then the string starts
+     with '/' plus an index off number (decimal).  */
+  char tmpbuf[sizeof (arhdr.ar_name) + 2];
 
   bool changed_header = memb->long_name_off != -1;
   if (changed_header)
@@ -1455,7 +1458,11 @@ do_oper_insert (int oper, const char *arfname, char **argv, int argc,
 
 	      /* Create the header.  */
 	      struct ar_hdr arhdr;
-	      char tmpbuf[sizeof (arhdr.ar_name) + 1];
+	      /* The ar_name is not actually zero teminated, but we
+		 need that for snprintf.  Also if the name is too
+		 long, then the string starts with '/' plus an index
+		 off number (decimal).  */
+	      char tmpbuf[sizeof (arhdr.ar_name) + 2];
 	      if (all->long_name_off == -1)
 		{
 		  size_t namelen = strlen (all->name);
@@ -1465,7 +1472,7 @@ do_oper_insert (int oper, const char *arfname, char **argv, int argc,
 		}
 	      else
 		{
-		  snprintf (tmpbuf, sizeof (arhdr.ar_name) + 1, "/%-*ld",
+		  snprintf (tmpbuf, sizeof (tmpbuf), "/%-*ld",
 			    (int) sizeof (arhdr.ar_name), all->long_name_off);
 		  memcpy (arhdr.ar_name, tmpbuf, sizeof (arhdr.ar_name));
 		}
diff --git a/src/arlib.c b/src/arlib.c
index c3cf47f..fc62a77 100644
--- a/src/arlib.c
+++ b/src/arlib.c
@@ -1,5 +1,5 @@
 /* Functions to handle creation of Linux archives.
-   Copyright (C) 2007-2012 Red Hat, Inc.
+   Copyright (C) 2007-2012, 2016 Red Hat, Inc.
    This file is part of elfutils.
    Written by Ulrich Drepper <drepper@redhat.com>, 2007.
 
@@ -23,6 +23,7 @@
 #include <assert.h>
 #include <error.h>
 #include <gelf.h>
+#include <inttypes.h>
 #include <libintl.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -107,6 +108,9 @@ arlib_init (void)
 void
 arlib_finalize (void)
 {
+  /* Note that the size is stored as decimal string in 10 chars,
+     without zero terminator (we add + 1 here only so snprintf can
+     put it at the end, we then don't use it when we memcpy it).  */
   char tmpbuf[sizeof (((struct ar_hdr *) NULL)->ar_size) + 1];
 
   symtab.longnameslen = obstack_object_size (&symtab.longnamesob);
@@ -121,7 +125,7 @@ arlib_finalize (void)
 
       symtab.longnames = obstack_finish (&symtab.longnamesob);
 
-      int s = snprintf (tmpbuf, sizeof (tmpbuf), "%-*zu",
+      int s = snprintf (tmpbuf, sizeof (tmpbuf), "%-*" PRId32 "",
 			(int) sizeof (((struct ar_hdr *) NULL)->ar_size),
 			symtab.longnameslen - sizeof (struct ar_hdr));
       memcpy (&((struct ar_hdr *) symtab.longnames)->ar_size, tmpbuf, s);
@@ -169,7 +173,7 @@ arlib_finalize (void)
 
   /* See comment for ar_date above.  */
   memcpy (&((struct ar_hdr *) symtab.symsoff)->ar_size, tmpbuf,
-	  snprintf (tmpbuf, sizeof (tmpbuf), "%-*zu",
+	  snprintf (tmpbuf, sizeof (tmpbuf), "%-*" PRId32 "",
 		    (int) sizeof (((struct ar_hdr *) NULL)->ar_size),
 		    symtab.symsofflen + symtab.symsnamelen
 		    - sizeof (struct ar_hdr)));
-- 
1.8.3.1