[PATCH v1.1] realpath: Bring back GNU extension on ENOENT and EACCES [BZ #28996]

[PATCH v1.1] realpath: Bring back GNU extension on ENOENT and EACCES [BZ #28996]

[Siddhesh Poyarekar]

The GNU extension for realpath states that if the path resolution fails
with ENOENT or EACCES and the resolved buffer is non-NULL, it will
contain part of the path that failed resolution.

commit 949ad78a189194048df8a253bb31d1d11d919044 broke this when it
omitted the copy on failure.  Bring it back partially to continue
supporting this GNU extension.

Resolves: BZ #28996

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 stdlib/canonicalize.c | 9 ++++++---
 stdlib/test-canon.c   | 4 ++--
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c
index 6237a41d42..e6566bd7d9 100644
--- a/stdlib/canonicalize.c
+++ b/stdlib/canonicalize.c
@@ -400,11 +400,14 @@ realpath_stk (const char *name, char *resolved,
 
 error:
   *dest++ = '\0';
-  if (!failed && resolved != NULL)
+  if (resolved != NULL)
     {
-      if (dest - rname <= get_path_max ())
+      /* Copy the full result on success or partial result if failure was due
+	 to the path not existing or not being accessible.  */
+      if ((!failed || errno == ENOENT || errno == EACCES)
+	  && dest - rname <= get_path_max ())
 	rname = strcpy (resolved, rname);
-      else
+      else if (!failed)
 	{
 	  failed = true;
 	  __set_errno (ENAMETOOLONG);
diff --git a/stdlib/test-canon.c b/stdlib/test-canon.c
index 2ad1218749..a9c83be17c 100644
--- a/stdlib/test-canon.c
+++ b/stdlib/test-canon.c
@@ -174,8 +174,8 @@ do_test (int argc, char ** argv)
 	  continue;
 	}
 
-      /* Only on success verify that buf contains the result too.  */
-      if (result != NULL
+      /* Verify buf contents if the call succeeded or failed with ENOENT.  */
+      if ((result != NULL || errno == ENOENT)
 	  && !check_path (buf, tests[i].out ? tests[i].out : tests[i].resolved))
 	{
 	  printf ("%s: flunked test %d (expected resolved `%s', got `%s')\n",
-- 
2.35.1

Re: [PATCH v1.1] realpath: Bring back GNU extension on ENOENT and EACCES [BZ #28996]

[Andreas Schwab]

On Mär 30 2022, Siddhesh Poyarekar via Libc-alpha wrote:

> The GNU extension for realpath states that if the path resolution fails
> with ENOENT or EACCES and the resolved buffer is non-NULL, it will
> contain part of the path that failed resolution.
>
> commit 949ad78a189194048df8a253bb31d1d11d919044 broke this when it
> omitted the copy on failure.  Bring it back partially to continue
> supporting this GNU extension.

Ok.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."