msnfs41client: Fix assert when reading a symlink to "/" from cmd.exe, 2025-06-28
Posted by Anonymous on Sat 28th Jun 2025 21:57
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From a50078e7e753be520e2fce37d6f78b7724fbc68e Mon Sep 17 00:00:00 2001
From: Roland Mainz <roland.mainz@nrubsig.org>
Date: Sat, 28 Jun 2025 22:51:32 +0200
Subject: [PATCH] daemon,tests: Fix EASSERT when reading symlink to "/"

Fix EASSERT when reading symlink to "/", and add a testcase for it.

Signed-off-by: Cedric Blancher <cedric.blancher@gmail.com>
---
 daemon/symlink.c         | 20 +++++++++++++++++++-
 tests/manual_testing.txt |  8 +++++++-
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/daemon/symlink.c b/daemon/symlink.c
index 99ab4fb..8ddd70e 100644
--- a/daemon/symlink.c
+++ b/daemon/symlink.c
@@ -59,7 +59,25 @@ static int abs_path_link(
     }
     /* if link is an absolute path, start path_pos at the beginning */
     else if (is_delimiter(*link)) {
-        path_pos = path->path;
+        if (link_len == 0) {
+            /* This should never happen... */
+            eprintf("abs_path_link(path_pos='%s', link='%.*s', link_len=%d): "
+                "Invalid path, link_len==0\n",
+                path_pos, (int)link_len, link, (int)link_len);
+            status = ERROR_BAD_NETPATH;
+            goto out;
+        }
+        else if (link_len == 1) {
+            /* Special case for $ ln -s '/' mysymlinktoroot # */
+            path_pos = path->path+1;
+            path->path[0] = '\\';
+            path->path[1] = '\0';
+            goto out;
+        }
+        else {
+            /* Normal absolute path... */
+            path_pos = path->path;
+        }
     }

     /* copy each component of link into the path */
diff --git a/tests/manual_testing.txt b/tests/manual_testing.txt
index c7e83fd..e491a78 100644
--- a/tests/manual_testing.txt
+++ b/tests/manual_testing.txt
@@ -275,7 +275,13 @@ rm -f symlink1_to_h_tmp ; cmd /C 'mklink /D symlink1_to_h_tmp \\derfwpc5131_ipv4
 #
 # all test should print "OK test <testnum>"
 # ("." is a relative symlink, just included here for more coverage)
-ksh93 -c 'typeset -a a=( "/" "/usr" "/tmp" "/usr/bin" "$PWD" "/dev/null" "." ) ; for ((i=0 ; i < ${#a[@]} ; i++ )) ; do rm -f "syml$i" ; ln -sf "${a[$i]}" "syml$i" ; l="$(readlink "syml$i")" ; if [[ "$l" == "${a[$i]}" ]] ; then printf "OK test %d\n" i ; else printf "FAIL test %d\n" i ; fi ; done'
+ksh93 -c 'typeset -a a=( "/" "/usr" "/usr/" "/tmp" "/usr/bin" "$PWD" "/dev/null" "." ) ; for ((i=0 ; i < ${#a[@]} ; i++ )) ; do rm -f "syml$i" ; ln -sf "${a[$i]}" "syml$i" ; l="$(readlink "syml$i")" ; if [[ "$l" == "${a[$i]}" ]] ; then printf "OK test %d\n" i ; else printf "FAIL test %d\n" i ; fi ; done'
+
+#
+# Test whether cmd.exe can follow symlink to "/" (root), which should point to C:cygwin64\ or C:\cygwin\
+# (CYGWIN='winsymlinks:nativestrict' is used so the same test works with NTFS too)
+#
+CYGWIN='winsymlinks:nativestrict' bash -c 'rm -f symlrootdotslash &&  ln -sf / symlrootdotslash && cmd /C "cd symlrootdotslash" && echo "Test OK"'

 #
 # Test for mkdir with UNC path
--
2.45.1