core: use readdir(3) with glibc, and associated cleanup

Starting with glibc-2.23 (i.e. what's in Fedora 25), readdir_r(3)
is marked as deprecated. Specifically the function decl in <dirent.h>
has the deprecated attribute, and now warnings are thrown during the
compile on Fedora 25 builds.

The readdir(_r)(3) man page (on Fedora 25 at least) and World+Dog say
that glibc's readdir(3) is, and always has been, MT-SAFE as long as
only one thread is accessing the directory object returned by opendir().
World+Dog also says there is a potential buffer overflow in readdir_r().
World+Dog suggests that it is preferable to simply use readdir(). There's
an implication that eventually readdir_r(3) will be removed from glibc.
POSIX has, apparently deprecated it in the standard, or even removed it
entirely.

Over and above that, our source near the various uses of readdir(_r)(3)
has a few unsafe uses of strcpy()+strcat().

(AFAIK nobody has looked at the readdir(3) implemenation in *BSD to see
if the same is true on those platforms, and we can't be sure of MacOS
even though we know it's based on *BSD.)

Change-Id: I5481f18ba1eebe7ee177895eecc9a80a71b60568
BUG: 1356998
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/14838
Smoke: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Niels de Vos <ndevos@redhat.com>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
Reviewed-by: Kotresh HR <khiremat@redhat.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>

1 files changed, 18 insertions, 1 deletions

diff --git a/libglusterfs/src/syscall.c b/libglusterfs/src/syscall.c
index 316d80452fb..93838e285a4 100644
--- a/libglusterfs/src/syscall.c
+++ b/libglusterfs/src/syscall.c
@@ -94,9 +94,26 @@ int sys_mkdirat(int dirfd, const char *pathname, mode_t mode)
 }
 
 struct dirent *
-sys_readdir (DIR *dir)
+sys_readdir (DIR *dir, struct dirent *de)
 {
+#if !defined(__GLIBC__)
+        /*
+         * World+Dog says glibc's readdir(3) is MT-SAFE as long as
+         * two threads are not accessing the same DIR; there's a
+         * potential buffer overflow in glibc's readdir_r(3); and
+         * glibc's readdir_r(3) is deprecated after version 2.22
+         * with presumed eventual removal.
+         * Given all that, World+Dog says everyone should just use
+         * readdir(3). But it's unknown, unclear whether the same
+         * is also true for *BSD, MacOS, and, etc.
+        */
+        struct dirent *entry = NULL;
+
+        (void) readdir_r (dir, de, &entry);
+        return entry;
+#else
         return readdir (dir);
+#endif
 }