elf: Fix pldd (BZ#18035)

Since 9182aa67994 (Fix vDSO l_name for GDB's, BZ#387) the initial link_map
for executable itself and loader will have both l_name and l_libname->name
holding the same value due:

 elf/dl-object.c

 95   new->l_name = *realname ? realname : (char *) newname->name + libname_len - 1;

Since newname->name points to new->l_libname->name.

This leads to pldd to an infinite call at:

 elf/pldd-xx.c

203     again:
204       while (1)
205         {
206           ssize_t n = pread64 (memfd, tmpbuf.data, tmpbuf.length, name_offset);

228           /* Try the l_libname element.  */
229           struct E(libname_list) ln;
230           if (pread64 (memfd, &ln, sizeof (ln), m.l_libname) == sizeof (ln))
231             {
232               name_offset = ln.name;
233               goto again;
234             }

Since the value at ln.name (l_libname->name) will be the same as previously
read. The straightforward fix is just avoid the check and read the new list
entry.

I checked also against binaries issues with old loaders with fix for BZ#387,
and pldd could dump the shared objects.

Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu, and
powerpc64le-linux-gnu.

	[BZ #18035]
	* elf/Makefile (tests-container): Add tst-pldd.
	* elf/pldd-xx.c: Use _Static_assert in of pldd_assert.
	(E(find_maps)): Avoid use alloca, use default read file operations
	instead of explicit LFS names, and fix infinite	loop.
	* elf/pldd.c: Explicit set _FILE_OFFSET_BITS, cleanup headers.
	(get_process_info): Use _Static_assert instead of assert, use default
	directory operations instead of explicit LFS names, and free some
	leadek pointers.
	* elf/tst-pldd.c: New file.

1 files changed, 118 insertions, 0 deletions

diff --git a/elf/tst-pldd.c b/elf/tst-pldd.c
new file mode 100644
index 0000000000..ed19cedd05
--- /dev/null
+++ b/elf/tst-pldd.c
@@ -0,0 +1,118 @@
+/* Basic tests for pldd program.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <libgen.h>
+#include <stdbool.h>
+
+#include <array_length.h>
+#include <gnu/lib-names.h>
+
+#include <support/subprocess.h>
+#include <support/capture_subprocess.h>
+#include <support/check.h>
+
+static void
+target_process (void *arg)
+{
+  pause ();
+}
+
+/* The test runs in a container because pldd does not support tracing
+   a binary started by the loader iself (as with testrun.sh).  */
+
+static int
+do_test (void)
+{
+  /* Create a copy of current test to check with pldd.  */
+  struct support_subprocess target = support_subprocess (target_process, NULL);
+
+  /* Run 'pldd' on test subprocess.  */
+  struct support_capture_subprocess pldd;
+  {
+    /* Three digits per byte plus null terminator.  */
+    char pid[3 * sizeof (uint32_t) + 1];
+    snprintf (pid, array_length (pid), "%d", target.pid);
+
+    const char prog[] = "/usr/bin/pldd";
+
+    pldd = support_capture_subprogram (prog,
+      (char *const []) { (char *) prog, pid, NULL });
+
+    support_capture_subprocess_check (&pldd, "pldd", 0, sc_allow_stdout);
+  }
+
+  /* Check 'pldd' output.  The test is expected to be linked against only
+     loader and libc.  */
+  {
+    pid_t pid;
+    char buffer[512];
+#define STRINPUT(size) "%" # size "s"
+
+    FILE *out = fmemopen (pldd.out.buffer, pldd.out.length, "r");
+    TEST_VERIFY (out != NULL);
+
+    /* First line is in the form of <pid>: <full path of executable>  */
+    TEST_COMPARE (fscanf (out, "%u: " STRINPUT (512), &pid, buffer), 2);
+
+    TEST_COMPARE (pid, target.pid);
+    TEST_COMPARE (strcmp (basename (buffer), "tst-pldd"), 0);
+
+    /* It expects only one loader and libc loaded by the program.  */
+    bool interpreter_found = false, libc_found = false;
+    while (fgets (buffer, array_length (buffer), out) != NULL)
+      {
+	/* Ignore vDSO.  */
+        if (buffer[0] != '/')
+	  continue;
+
+	/* Remove newline so baseline (buffer) can compare against the
+	   LD_SO and LIBC_SO macros unmodified.  */
+	if (buffer[strlen(buffer)-1] == '\n')
+	  buffer[strlen(buffer)-1] = '\0';
+
+	if (strcmp (basename (buffer), LD_SO) == 0)
+	  {
+	    TEST_COMPARE (interpreter_found, false);
+	    interpreter_found = true;
+	    continue;
+	  }
+
+	if (strcmp (basename (buffer), LIBC_SO) == 0)
+	  {
+	    TEST_COMPARE (libc_found, false);
+	    libc_found = true;
+	    continue;
+	  }
+      }
+    TEST_COMPARE (interpreter_found, true);
+    TEST_COMPARE (libc_found, true);
+
+    fclose (out);
+  }
+
+  support_capture_subprocess_free (&pldd);
+  support_process_terminate (&target);
+
+  return 0;
+}
+
+#include <support/test-driver.c>