Subject: Re: bug#11453: `ls` in coreutils-8.17 incorrectly shows broken symlinks in /
From: Jim Meyering <[email-masked]>
To: Mike Frysinger <[email-masked]>
Cc: [email-masked]
Date: Sat, 12 May 2012 16:27:33 +0200
List-Id: <debbugs-submit.debbugs.gnu.org>

Jim Meyering wrote:
> Jim Meyering wrote:
>> Mike Frysinger wrote:
>>> coreutils-8.16 works fine (confirmed), and i don't recall seeing this bug
>>> before, so looks like a regression with 8.17
>>>
>>> easy to show:
>>> $ sudo ln -s dev /foo
>>> $ ls --color=auto /
>>> ... foo wrongly shows up in blinky text indicating it's a broken symlink ...
>>> $ ls --color=auto /.
>>> ... foo correctly shows up with normal coloring indicating it's a symlink ...
>>> $ cd / ; ls --color=auto
>>> ... foo correctly shows up with normal coloring indicating it's a symlink ...
>>> -mike
>>
>> Rats.
>> That bug was introduced by my clean-up.
>> Here's the probable fix.
>> Thanks for the report!
>>
>> diff --git a/src/ls.c b/src/ls.c
>> index 397e4ea..b548382 100644
>> --- a/src/ls.c
>> +++ b/src/ls.c
>> @@ -3213,7 +3213,8 @@ make_link_name (char const *name, char const *linkname)
>>      return xstrdup (linkname);
>>
>>    char *p = xmalloc (prefix_len + 1 + strlen (linkname) + 1);
>> -  stpcpy (stpncpy (p, name, prefix_len + 1), linkname);
>> +  bool prefix_ends_in_slash = ISSLASH (name[prefix_len - 1]);
>> +  stpcpy (stpncpy (p, name, prefix_len + !prefix_ends_in_slash), linkname);
>
> Humph.  That's wrong, too.

Actually it's fine.
Here's that same semantic change, presented in a more readable manner,
along with NEWS and a new test.

The only way I found to reproduce this problem without write access
to "/" is if there's already an entry there that is a non-dangling
symlink-to-relative-name.  Since those exist on Fedora 17 (/lib -> /usr/lib,
/bin -> /usr/bin, etc.) and on Debian unstable, (I see relative vmlinuz
and initrd.img links), that seems good enough.  It's not worth the cost
of an additional root-only test just to ensure this bug doesn't sneak
back in.

From 6124a3842dfa8484b52e067a8ab8105c3875a4f7 Mon Sep 17 00:00:00 2001
From: Jim Meyering <[email-masked]>
Date: Thu, 10 May 2012 19:43:00 +0200
Subject: [PATCH] ls: color each symlink-to-relative-name in / properly

In order for ls --color to color each symlink, it must form the name
of each referent and then stat it to see if the link is dangling, to
a directory, to a file, etc.  When the symlink is to a relative name,
ls must concatenate the starting directory name and that relative name.
When, in addition, the starting directory was "/" or "/some-name",
the result was ill-formed, and the subsequent stat would usually fail,
making the caller color it as a dangling symlink.
* src/ls.c (make_link_name): Don't botch the case in which
dir_name(NAME) == "/" and LINKNAME is relative.
* tests/ls/root-rel-symlink-color: New file.  Test for the above.
* tests/Makefile.am (TESTS): Add it.
* NEWS (Bug fixes): Mention it.
Reported by Mike Frysinger in http://bugs.gnu.org/11453
Bug introduced by commit v8.16-23-gbcb9078.
---
 NEWS                            |  5 ++++
 src/ls.c                        |  9 +++++++-
 tests/Makefile.am               |  1 +
 tests/ls/root-rel-symlink-color | 51 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 65 insertions(+), 1 deletion(-)
 create mode 100755 tests/ls/root-rel-symlink-color

diff --git a/NEWS b/NEWS
index 6c620b3..f9e9c70 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,11 @@ GNU coreutils NEWS                                    -*- outline -*-

 * Noteworthy changes in release ?.? (????-??-??) [?]

+** Bug fixes
+
+  ls --color would mis-color relative-named symlinks in /
+  [bug introduced in coreutils-8.17]
+

 * Noteworthy changes in release 8.17 (2012-05-10) [stable]

diff --git a/src/ls.c b/src/ls.c
index 397e4ea..9494ae9 100644
--- a/src/ls.c
+++ b/src/ls.c
@@ -3213,7 +3213,14 @@ make_link_name (char const *name, char const *linkname)
     return xstrdup (linkname);

   char *p = xmalloc (prefix_len + 1 + strlen (linkname) + 1);
-  stpcpy (stpncpy (p, name, prefix_len + 1), linkname);
+
+  /* PREFIX_LEN usually specifies a string not ending in slash.
+     In that case, extend it by one, since the next byte *is* a slash.
+     Otherwise, the prefix is "/", so leave the length unchanged.  */
+  if ( ! ISSLASH (name[prefix_len - 1]))
+    ++prefix_len;
+
+  stpcpy (stpncpy (p, name, prefix_len), linkname);
   return p;
 }

diff --git a/tests/Makefile.am b/tests/Makefile.am
index a4370a6..0bafc5f 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -449,6 +449,7 @@ TESTS =						\
   ls/proc-selinux-segfault			\
   ls/readdir-mountpoint-inode			\
   ls/recursive					\
+  ls/root-rel-symlink-color			\
   ls/rt-1					\
   ls/slink-acl					\
   ls/stat-dtype					\
diff --git a/tests/ls/root-rel-symlink-color b/tests/ls/root-rel-symlink-color
new file mode 100755
index 0000000..d795432
--- /dev/null
+++ b/tests/ls/root-rel-symlink-color
@@ -0,0 +1,51 @@
+#!/bin/sh
+# Exercise the 8.17 ls bug with coloring relative-named symlinks in "/".
+
+# Copyright (C) 2012 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/init.sh"; path_prepend_ ../src
+print_ver_ ls
+
+symlink_to_rel=
+for i in /*; do
+  # Skip non-symlinks:
+  env test -h "$i" || continue
+
+  # Skip dangling symlinks:
+  env test -e "$i" || continue
+
+  # Skip any symlink-to-absolute-name:
+  case $(readlink "$i") in /*) continue ;; esac
+
+  symlink_to_rel=$i
+  break
+done
+
+test -z "$symlink_to_rel" \
+  && skip_ no relative symlink in /
+
+e='\33'
+color_code='01;36'
+c_pre="$e[0m$e[${color_code}m"
+c_post="$e[0m"
+printf "$c_pre$symlink_to_rel$c_post\n" > exp || framework_failure_
+
+env TERM=xterm LS_COLORS="ln=$color_code:or=1;31;42" \
+  ls -d --color=always "$symlink_to_rel" > out || fail=1
+
+compare exp out || fail=1
+
+Exit $fail
--
1.7.10.2.484.gcd07cc5