From: Bruno Haible <bruno@clisp.org>
Date: Thu, 14 Aug 2025 20:18:57 +0000 (+0200)
Subject: fchmodat: Use issymlinkat.
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2f0b2ccec3c91a61515a2bf1d6ac9aa9d1ff30c9;p=thirdparty%2Fgnulib.git

fchmodat: Use issymlinkat.

* lib/fchmodat.c (fchmodat): Use issymlinkat instead of readlinkat.
* modules/fchmodat (Depends-on): Add issymlinkat, openat.
---

diff --git a/ChangeLog b/ChangeLog
index 9df8c9b99b..386c8bd475 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2025-08-14  Bruno Haible  <bruno@clisp.org>
+
+	fchmodat: Use issymlinkat.
+	* lib/fchmodat.c (fchmodat): Use issymlinkat instead of readlinkat.
+	* modules/fchmodat (Depends-on): Add issymlinkat, openat.
+
 2025-08-14  Bruno Haible  <bruno@clisp.org>
 
 	lchmod: Use issymlink, issymlinkat.
diff --git a/lib/fchmodat.c b/lib/fchmodat.c
index eb82e1cafb..57222e58eb 100644
--- a/lib/fchmodat.c
+++ b/lib/fchmodat.c
@@ -84,8 +84,6 @@ fchmodat (int dir, char const *file, mode_t mode, int flags)
   if (flags == AT_SYMLINK_NOFOLLOW)
     {
 #  if HAVE_READLINKAT
-      char readlink_buf[1];
-
 #   ifdef O_PATH
       /* Open a file descriptor with O_NOFOLLOW, to make sure we don't
          follow symbolic links, if /proc is mounted.  O_PATH is used to
@@ -96,17 +94,20 @@ fchmodat (int dir, char const *file, mode_t mode, int flags)
         return fd;
 
       int err;
-      if (0 <= readlinkat (fd, "", readlink_buf, sizeof readlink_buf))
-        err = EOPNOTSUPP;
-      else if (errno == EINVAL)
-        {
-          static char const fmt[] = "/proc/self/fd/%d";
-          char buf[sizeof fmt - sizeof "%d" + INT_BUFSIZE_BOUND (int)];
-          sprintf (buf, fmt, fd);
-          err = chmod (buf, mode) == 0 ? 0 : errno == ENOENT ? -1 : errno;
-        }
-      else
-        err = errno == ENOENT ? -1 : errno;
+      {
+        int ret = issymlinkat (fd, "");
+        if (ret > 0)
+          err = EOPNOTSUPP;
+        else if (ret == 0)
+          {
+            static char const fmt[] = "/proc/self/fd/%d";
+            char buf[sizeof fmt - sizeof "%d" + INT_BUFSIZE_BOUND (int)];
+            sprintf (buf, fmt, fd);
+            err = chmod (buf, mode) == 0 ? 0 : errno == ENOENT ? -1 : errno;
+          }
+        else
+          err = errno == ENOENT ? -1 : errno;
+      }
 
       close (fd);
 
@@ -117,7 +118,7 @@ fchmodat (int dir, char const *file, mode_t mode, int flags)
 
       /* O_PATH + /proc is not supported.  */
 
-      if (0 <= readlinkat (dir, file, readlink_buf, sizeof readlink_buf))
+      if (issymlinkat (dir, file) > 0)
         {
           errno = EOPNOTSUPP;
           return -1;
diff --git a/modules/fchmodat b/modules/fchmodat
index 3afd0efd30..914825c1a4 100644
--- a/modules/fchmodat
+++ b/modules/fchmodat
@@ -14,6 +14,8 @@ fcntl-h         [test $HAVE_FCHMODAT = 0 || test $REPLACE_FCHMODAT = 1]
 unistd-h        [test $HAVE_FCHMODAT = 0 || test $REPLACE_FCHMODAT = 1]
 intprops        [test $HAVE_FCHMODAT = 0 || test $REPLACE_FCHMODAT = 1]
 c99             [test $REPLACE_FCHMODAT = 1]
+issymlinkat     [test $REPLACE_FCHMODAT = 1]
+openat          [test $REPLACE_FCHMODAT = 1]
 at-internal     [test $HAVE_FCHMODAT = 0]
 chmod           [test $HAVE_FCHMODAT = 0]
 extern-inline   [test $HAVE_FCHMODAT = 0]