From 0093ac8d57a0f1a16fd09d98f6a524dddb6053e7 Mon Sep 17 00:00:00 2001
From: Jim Meyering <address@hidden>
Date: Thu, 13 Mar 2014 17:05:04 -0700
Subject: [PATCH] ln: with -sr, don't segfault for a TARGET of ''

Prior to this change, "ln -sr '' F" would segfault, attempting
to read path2[1] in relpath.c's path_common_prefix function.
This problem arises whenever canonicalize_filename_mode returns
NULL.
* src/ln.c (convert_abs_rel): Call relpath only when
both canonicalize_filename_mode calls return non-NULL.
* tests/ln/relative.sh: Add a test to trigger this failure.
* THANKS.in: List reporter's name/address.
* NEWS (Bug fixes): Mention it.
Reported by Erik Bernstein in address@hidden
Fixes http://bugs.gnu.org/17010.
---
 NEWS                 |  3 +++
 THANKS.in            |  1 +
 src/ln.c             | 16 ++++++++++------
 tests/ln/relative.sh |  5 +++++
 4 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/NEWS b/NEWS
index 62966b2..35d48e5 100644
--- a/NEWS
+++ b/NEWS
@@ -25,6 +25,9 @@ GNU coreutils NEWS                                    -*- outline -*-
   it would display an error, requiring --no-dereference to avoid the issue.
   [bug introduced in coreutils-5.3.0]

+  ln -sr '' F no longer segfaults.  Now works as expected.
+  [bug introduced with the --relative feature in coreutils-8.16]
+
   shuf --repeat no longer dumps core if the input is empty.
   [bug introduced with the --repeat feature in coreutils-8.22]

diff --git a/THANKS.in b/THANKS.in
index 561d18c..2670265 100644
--- a/THANKS.in
+++ b/THANKS.in
@@ -193,6 +193,7 @@ Eric G. Miller                      address@hidden
 Eric Pemente                        address@hidden
 Eric S. Raymond                     address@hidden
 Erik Bennett                        address@hidden
+Erik Bernstein                      address@hidden
 Erik Corry                          address@hidden
 Felix Lee                           address@hidden
 Felix Rauch Valenti                 address@hidden
diff --git a/src/ln.c b/src/ln.c
index aab9cf2..6726699 100644
--- a/src/ln.c
+++ b/src/ln.c
@@ -149,13 +149,17 @@ convert_abs_rel (const char *from, const char *target)
   char *realdest = canonicalize_filename_mode (targetdir, CAN_MISSING);
   char *realfrom = canonicalize_filename_mode (from, CAN_MISSING);

-  /* Write to a PATH_MAX buffer.  */
-  char *relative_from = xmalloc (PATH_MAX);
-
-  if (!relpath (realfrom, realdest, relative_from, PATH_MAX))
+  char *relative_from = NULL;
+  if (realdest && realfrom)
     {
-      free (relative_from);
-      relative_from = NULL;
+      /* Write to a PATH_MAX buffer.  */
+      relative_from = xmalloc (PATH_MAX);
+
+      if (!relpath (realfrom, realdest, relative_from, PATH_MAX))
+        {
+          free (relative_from);
+          relative_from = NULL;
+        }
     }

   free (targetdir);
diff --git a/tests/ln/relative.sh b/tests/ln/relative.sh
index 7636695..5cf280a 100755
--- a/tests/ln/relative.sh
+++ b/tests/ln/relative.sh
@@ -45,4 +45,9 @@ mkdir web
 ln -sr latest web/latest
 test $(readlink web/latest) = '../release2' || fail=1

+# Expect this to fail with exit status 1, or to succeed quietly (freebsd).
+# Prior to coreutils-8.23, it would segfault.
+ln -sr '' F
+case $? in [01]) ;; *) fail=1;; esac
+
 Exit $fail
-- 
1.9.0.167.g384364b