[glibc] realpath: Do not copy result on failure (BZ #28815)

[glibc] realpath: Do not copy result on failure (BZ #28815)

[Siddhesh Poyarekar]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=949ad78a189194048df8a253bb31d1d11d919044

commit 949ad78a189194048df8a253bb31d1d11d919044
Author: Siddhesh Poyarekar <siddhesh@sourceware.org>
Date:   Mon Feb 21 08:26:06 2022 +0530

    realpath: Do not copy result on failure (BZ #28815)
    
    On failure, the contents of the resolved buffer passed in by the caller
    to realpath are undefined.  Do not copy any partial resolution to the
    buffer and also do not test resolved contents in test-canon.c.
    
    Resolves: BZ #28815
    
    Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Diff:
---
 stdlib/canonicalize.c | 4 ++--
 stdlib/test-canon.c   | 4 +++-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c
index 6caed9e70e..6237a41d42 100644
--- a/stdlib/canonicalize.c
+++ b/stdlib/canonicalize.c
@@ -400,11 +400,11 @@ realpath_stk (const char *name, char *resolved,
 
 error:
   *dest++ = '\0';
-  if (resolved != NULL)
+  if (!failed && resolved != NULL)
     {
       if (dest - rname <= get_path_max ())
 	rname = strcpy (resolved, rname);
-      else if (!failed)
+      else
 	{
 	  failed = true;
 	  __set_errno (ENAMETOOLONG);
diff --git a/stdlib/test-canon.c b/stdlib/test-canon.c
index 185ccf4f48..2ad1218749 100644
--- a/stdlib/test-canon.c
+++ b/stdlib/test-canon.c
@@ -174,7 +174,9 @@ do_test (int argc, char ** argv)
 	  continue;
 	}
 
-      if (!check_path (buf, tests[i].out ? tests[i].out : tests[i].resolved))
+      /* Only on success verify that buf contains the result too.  */
+      if (result != NULL
+	  && !check_path (buf, tests[i].out ? tests[i].out : tests[i].resolved))
 	{
 	  printf ("%s: flunked test %d (expected resolved `%s', got `%s')\n",
 		  argv[0], i, tests[i].out ? tests[i].out : tests[i].resolved,