Revert "checkpath: use O_PATH when available"

This reverts commit 2af0cedd59.

After speaking with Luis Ressel on the Gentoo selinux team, I am reverting
this commit for the following reasons:

- Luis told me that he feels this is not the solution we need to address
  the concern with checkpath; I will be working with him on another
  solution.

- There are concerns about the way the path variable was handled
  and the assert() call.
  The path variable should be dynamically allocated using xasprintf
  instead of defining a length at compile time. This would eliminate the
  need for the assert() call.

- It introduces the definition of _GNU_SOURCE which makes it
  easier to introduce portability concerns in the future (see #262).

src/rc/checkpath.c

@@ -16,11 +16,9 @@
  *    except according to the terms contained in the LICENSE file.
  */
 
-#define _GNU_SOURCE
 #include <sys/types.h>
 #include <sys/stat.h>
 
-#include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <getopt.h>
@@ -71,37 +69,6 @@ const char * const longopts_help[] = {
 };
 const char *usagestring = NULL;
 
-/* On Linux, fchmod() returns EBADF when passed a file descriptor opened
- * with O_PATH. Use chmod() on /proc/self/fd as a workaround. */
-static int fchmod_opath(int fd, mode_t mode)
-{
-#ifdef O_PATH
-	/* A 64-bit int will result in a maximum path length of 35 characters. */
-	char path[35];
-
-	/* Maybe we will have 128-bit ints someday. */
-	assert(sizeof(int) <= 8);
-
-	if (sprintf(path, "/proc/self/fd/%d", fd) < 0)
-		return -1;
-
-	return chmod(path, mode);
-#else
-	return fchmod(fd, mode);
-#endif
-}
-
-/* On Linux, fchown() returns EBADF when passed a file descriptor opened
- * with O_PATH. fchownat() does not exhibit this flaw. */
-static int fchown_opath(int fd, uid_t uid, gid_t gid)
-{
-#ifdef O_PATH
-	return fchownat(fd, "", uid, gid, AT_EMPTY_PATH);
-#else
-	return fchown(fd, uid, gid);
-#endif
-}
-
 static int do_check(char *path, uid_t uid, gid_t gid, mode_t mode,
 	inode_t type, bool trunc, bool chowner, bool selinux_on)
 {
@@ -115,7 +82,7 @@ static int do_check(char *path, uid_t uid, gid_t gid, mode_t mode,
 
 	memset(&st, 0, sizeof(st));
 	flags = O_CREAT|O_NDELAY|O_WRONLY|O_NOCTTY;
-	readflags = O_NDELAY|O_NOCTTY;
+	readflags = O_NDELAY|O_NOCTTY|O_RDONLY;
 #ifdef O_CLOEXEC
 	flags |= O_CLOEXEC;
 	readflags |= O_CLOEXEC;
@@ -123,11 +90,6 @@ static int do_check(char *path, uid_t uid, gid_t gid, mode_t mode,
 #ifdef O_NOFOLLOW
 	flags |= O_NOFOLLOW;
 	readflags |= O_NOFOLLOW;
-#endif
-#ifdef O_PATH
-	readflags |= O_PATH;
-#else
-	readflags |= O_RDONLY;
 #endif
 	if (trunc)
 		flags |= O_TRUNC;
@@ -215,7 +177,7 @@ static int do_check(char *path, uid_t uid, gid_t gid, mode_t mode,
 				return -1;
 			}
 			einfo("%s: correcting mode", path);
-			if (fchmod_opath(readfd, mode)) {
+			if (fchmod(readfd, mode)) {
 				eerror("%s: chmod: %s", applet, strerror(errno));
 				close(readfd);
 				return -1;
@@ -234,7 +196,7 @@ static int do_check(char *path, uid_t uid, gid_t gid, mode_t mode,
 				return -1;
 			}
 			einfo("%s: correcting owner", path);
-			if (fchown_opath(readfd, uid, gid)) {
+			if (fchown(readfd, uid, gid)) {
 				eerror("%s: chown: %s", applet, strerror(errno));
 				close(readfd);
 				return -1;