dlfcn: Deprecate dlinfo request type RTLD_DI_ORIGIN (bug #24298)

Commit b52619f2e8 added a new dlinfo
request type, RTLD_DI_ORIGIN_PATH, to be used instead of RTLD_DI_ORIGIN
which is prone to buffer overflows.  With a replacement available,
RTLD_DI_ORIGIN can now be deprecated.

This commit deprecates RTLD_DI_ORIGIN by adding a compile-time warning
upon its use, and documents the deprecation in the manual.

The warning depends on "Enumerator Attributes" supported by gcc
since 6.1 and by clang.  A new macro __attribute_deprecated_enum__,
analogous to __attribute_deprecated_msg__, is defined in cdefs.h.
Because gnulib can override system-installed cdefs.h, thus hiding our
definition, the deprecation is conditional on the macro being defined.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

dlfcn/dlfcn.h

@@ -145,8 +145,13 @@ enum
     RTLD_DI_SERINFOSIZE = 5,
 
     /* Treat ARG as `char *', and store there the directory name used to
-       expand $ORIGIN in this shared object's dependency file names.  */
-    RTLD_DI_ORIGIN = 6,
+       expand $ORIGIN in this shared object's dependency file names.
+       Deprecated due to potential for buffer overflows.  */
+    RTLD_DI_ORIGIN
+# ifdef __attribute_deprecated_enum__
+      __attribute_deprecated_enum__ ("Use RTLD_DI_ORIGIN_PATH instead")
+# endif
+      = 6,
 
     RTLD_DI_PROFILENAME = 7,	/* Unsupported, defined by Solaris.  */
     RTLD_DI_PROFILEOUT = 8,	/* Unsupported, defined by Solaris.  */

dlfcn/dlinfo.c

@@ -22,6 +22,7 @@
 #include <libintl.h>
 #include <dl-tls.h>
 #include <shlib-compat.h>
+#include <libc-diag.h>
 
 struct dlinfo_args
 {
@@ -63,9 +64,13 @@ dlinfo_doit (void *argsblock)
       _dl_rtld_di_serinfo (l, args->arg, true);
       break;
 
+    DIAG_PUSH_NEEDS_COMMENT;
+    DIAG_IGNORE_NEEDS_COMMENT (6.1, "-Wdeprecated-declarations");
+    /* Deprecated via compile-time warning due to buffer overflow risk.  */
     case RTLD_DI_ORIGIN:
       strcpy (args->arg, l->l_origin);
       break;
+    DIAG_POP_NEEDS_COMMENT;
 
     case RTLD_DI_ORIGIN_PATH:
       if (l->l_origin != (char *) -1)

dlfcn/tst-dlinfo.c

@@ -21,6 +21,7 @@
 #include <stdlib.h>
 #include <error.h>
 #include <support/check.h>
+#include <libc-diag.h>
 
 #define TEST_FUNCTION do_test ()
 
@@ -51,11 +52,15 @@ do_test (void)
 	}
     }
 
+  DIAG_PUSH_NEEDS_COMMENT;
+  /* Ignore deprecation to be able to test deprecated request type.  */
+  DIAG_IGNORE_NEEDS_COMMENT (6.1, "-Wdeprecated-declarations");
   char origin[8192];		/* >= PATH_MAX, in theory */
   TRY (RTLD_DI_ORIGIN, origin)
     {
       printf ("origin: %s\n", origin);
     }
+  DIAG_POP_NEEDS_COMMENT;
 
   const char *origin_path;
   TRY (RTLD_DI_ORIGIN_PATH, &origin_path)

manual/dynlink.texi

@@ -569,9 +569,9 @@ The value of the @code{$ORIGIN} dynamic string token for @var{handle} is
 written to the character array starting at @var{arg} as a
 null-terminated string.
 
-This request type should not be used because it is prone to buffer
-overflows.  Instead, @code{RTLD_DI_ORIGIN_PATH} described above should be
-used.
+This request type has been deprecated because it is prone to buffer
+overflows and should therefore not be used.  Instead,
+@code{RTLD_DI_ORIGIN_PATH} described above should be used.
 
 @item RTLD_DI_SERINFO
 @itemx RTLD_DI_SERINFOSIZE

misc/sys/cdefs.h

@@ -523,6 +523,15 @@
 # define __attribute_deprecated_msg__(msg) __attribute_deprecated__
 #endif
 
+/* Since version 6.1, gcc allows marking deprecated enumerators.  */
+#if __GNUC_PREREQ (6, 1) \
+    || __glibc_has_extension (__enumerator_attributes__)
+# define __attribute_deprecated_enum__(msg) \
+         __attribute__ ((__deprecated__ (msg)))
+#else
+# define __attribute_deprecated_enum__(msg) /* Ignore */
+#endif
+
 /* At some point during the gcc 2.8 development the `format_arg' attribute
    for functions was introduced.  We don't want to use it unconditionally
    (although this would be possible) since it generates warnings.