This patch is a rework of the following upstream patch:

commit 1a4c27355e146b6d8cc6487b998462c7fdd1048f

Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>

Date:   Thu Apr 11 18:12:00 2019 -0300

    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.

diff -Nrup a/elf/Makefile b/elf/Makefile

--- a/elf/Makefile	2019-05-17 12:35:12.663074766 -0400

+++ b/elf/Makefile	2019-05-17 12:35:45.816147975 -0400

@@ -201,6 +201,7 @@ tests-internal += loadtest unload unload

 	 neededtest neededtest2 neededtest3 neededtest4 \

 	 tst-tls3 tst-tls6 tst-tls7 tst-tls8 tst-dlmopen2 \

 	 tst-ptrguard1 tst-stackguard1 tst-libc_dlvsym

+tests-container += tst-pldd

 ifeq ($(build-hardcoded-path-in-tests),yes)

 tests += tst-dlopen-aout

 tst-dlopen-aout-no-pie = yes

diff -Nrup a/elf/pldd.c b/elf/pldd.c

--- a/elf/pldd.c	2018-08-01 01:10:47.000000000 -0400

+++ b/elf/pldd.c	2019-05-17 12:35:45.817147947 -0400

@@ -17,23 +17,17 @@

    License along with the GNU C Library; if not, see

    <http://www.gnu.org/licenses/>.  */

-#include <alloca.h>

+#define _FILE_OFFSET_BITS 64

+

 #include <argp.h>

-#include <assert.h>

 #include <dirent.h>

-#include <elf.h>

-#include <errno.h>

 #include <error.h>

 #include <fcntl.h>

 #include <libintl.h>

-#include <link.h>

-#include <stddef.h>

 #include <stdio.h>

 #include <stdlib.h>

-#include <string.h>

 #include <unistd.h>

 #include <sys/ptrace.h>

-#include <sys/stat.h>

 #include <sys/wait.h>

 #include <scratch_buffer.h>

@@ -76,14 +70,8 @@ static struct argp argp =

   options, parse_opt, args_doc, doc, NULL, more_help, NULL

 };

-// File descriptor of /proc/*/mem file.

-static int memfd;

-

-/* Name of the executable  */

-static char *exe;

-

 /* Local functions.  */

-static int get_process_info (int dfd, long int pid);

+static int get_process_info (const char *exe, int dfd, long int pid);

 static void wait_for_ptrace_stop (long int pid);

@@ -102,8 +90,10 @@ main (int argc, char *argv[])

       return 1;

     }

-  assert (sizeof (pid_t) == sizeof (int)

-	  || sizeof (pid_t) == sizeof (long int));

+  _Static_assert (sizeof (pid_t) == sizeof (int)

+                 || sizeof (pid_t) == sizeof (long int),

+                 "sizeof (pid_t) != sizeof (int) or sizeof (long int)");

+

   char *endp;

   errno = 0;

   long int pid = strtol (argv[remaining], &endp, 10);

@@ -119,25 +109,24 @@ main (int argc, char *argv[])

   if (dfd == -1)

     error (EXIT_FAILURE, errno, gettext ("cannot open %s"), buf);

-  struct scratch_buffer exebuf;

-  scratch_buffer_init (&exebuf);

+  /* Name of the executable  */

+  struct scratch_buffer exe;

+  scratch_buffer_init (&exe;;

   ssize_t nexe;

   while ((nexe = readlinkat (dfd, "exe",

-			     exebuf.data, exebuf.length)) == exebuf.length)

+                            exe.data, exe.length)) == exe.length)

     {

-      if (!scratch_buffer_grow (&exebuf))

+      if (!scratch_buffer_grow (&exe))

 	{

 	  nexe = -1;

 	  break;

 	}

     }

   if (nexe == -1)

-    exe = (char *) "<program name undetermined>";

+    /* Default stack allocation is at least 1024.  */

+    snprintf (exe.data, exe.length, "<program name undetermined>");

   else

-    {

-      exe = exebuf.data;

-      exe[nexe] = '\0';

-    }

+    ((char*)exe.data)[nexe] = '\0';

   /* Stop all threads since otherwise the list of loaded modules might

      change while we are reading it.  */

@@ -155,8 +144,8 @@ main (int argc, char *argv[])

     error (EXIT_FAILURE, errno, gettext ("cannot prepare reading %s/task"),

 	   buf);

-  struct dirent64 *d;

-  while ((d = readdir64 (dir)) != NULL)

+  struct dirent *d;

+  while ((d = readdir (dir)) != NULL)

     {

       if (! isdigit (d->d_name[0]))

 	continue;

@@ -182,7 +171,7 @@ main (int argc, char *argv[])

       wait_for_ptrace_stop (tid);

-      struct thread_list *newp = alloca (sizeof (*newp));

+      struct thread_list *newp = xmalloc (sizeof (*newp));

       newp->tid = tid;

       newp->next = thread_list;

       thread_list = newp;

@@ -190,17 +179,22 @@ main (int argc, char *argv[])

   closedir (dir);

-  int status = get_process_info (dfd, pid);

+  if (thread_list == NULL)

+    error (EXIT_FAILURE, 0, gettext ("no valid %s/task entries"), buf);

+

+  int status = get_process_info (exe.data, dfd, pid);

-  assert (thread_list != NULL);

   do

     {

       ptrace (PTRACE_DETACH, thread_list->tid, NULL, NULL);

+      struct thread_list *prev = thread_list;

       thread_list = thread_list->next;

+      free (prev);

     }

   while (thread_list != NULL);

   close (dfd);

+  scratch_buffer_free (&exe;;

   return status;

 }

@@ -281,9 +275,10 @@ warranty; not even for MERCHANTABILITY o

 static int

-get_process_info (int dfd, long int pid)

+get_process_info (const char *exe, int dfd, long int pid)

 {

-  memfd = openat (dfd, "mem", O_RDONLY);

+  /* File descriptor of /proc/<pid>/mem file.  */

+  int memfd = openat (dfd, "mem", O_RDONLY);

   if (memfd == -1)

     goto no_info;

@@ -333,9 +328,9 @@ get_process_info (int dfd, long int pid)

   int retval;

   if (e_ident[EI_CLASS] == ELFCLASS32)

-    retval = find_maps32 (pid, auxv, auxv_size);

+    retval = find_maps32 (exe, memfd, pid, auxv, auxv_size);

   else

-    retval = find_maps64 (pid, auxv, auxv_size);

+    retval = find_maps64 (exe, memfd, pid, auxv, auxv_size);

   free (auxv);

   close (memfd);

diff -Nrup a/elf/pldd-xx.c b/elf/pldd-xx.c

--- a/elf/pldd-xx.c	2018-08-01 01:10:47.000000000 -0400

+++ b/elf/pldd-xx.c	2019-05-17 13:05:29.587147445 -0400

@@ -23,10 +23,6 @@

 #define EW_(e, w, t) EW__(e, w, _##t)

 #define EW__(e, w, t) e##w##t

-#define pldd_assert(name, exp) \

-  typedef int __assert_##name[((exp) != 0) - 1]

-

-

 struct E(link_map)

 {

   EW(Addr) l_addr;

@@ -39,12 +35,12 @@ struct E(link_map)

   EW(Addr) l_libname;

 };

 #if CLASS == __ELF_NATIVE_CLASS

-pldd_assert (l_addr, (offsetof (struct link_map, l_addr)

-			== offsetof (struct E(link_map), l_addr)));

-pldd_assert (l_name, (offsetof (struct link_map, l_name)

-			== offsetof (struct E(link_map), l_name)));

-pldd_assert (l_next, (offsetof (struct link_map, l_next)

-			== offsetof (struct E(link_map), l_next)));

+_Static_assert (offsetof (struct link_map, l_addr)

+               == offsetof (struct E(link_map), l_addr), "l_addr");

+_Static_assert (offsetof (struct link_map, l_name)

+               == offsetof (struct E(link_map), l_name), "l_name");

+_Static_assert (offsetof (struct link_map, l_next)

+               == offsetof (struct E(link_map), l_next), "l_next");

 #endif

@@ -54,10 +50,10 @@ struct E(libname_list)

   EW(Addr) next;

 };

 #if CLASS == __ELF_NATIVE_CLASS

-pldd_assert (name, (offsetof (struct libname_list, name)

-		      == offsetof (struct E(libname_list), name)));

-pldd_assert (next, (offsetof (struct libname_list, next)

-		      == offsetof (struct E(libname_list), next)));

+_Static_assert (offsetof (struct libname_list, name)

+               == offsetof (struct E(libname_list), name), "name");

+_Static_assert (offsetof (struct libname_list, next)

+               == offsetof (struct E(libname_list), next), "next");

 #endif

 struct E(r_debug)

@@ -69,16 +65,17 @@ struct E(r_debug)

   EW(Addr) r_map;

 };

 #if CLASS == __ELF_NATIVE_CLASS

-pldd_assert (r_version, (offsetof (struct r_debug, r_version)

-			   == offsetof (struct E(r_debug), r_version)));

-pldd_assert (r_map, (offsetof (struct r_debug, r_map)

-		       == offsetof (struct E(r_debug), r_map)));

+_Static_assert (offsetof (struct r_debug, r_version)

+               == offsetof (struct E(r_debug), r_version), "r_version");

+_Static_assert (offsetof (struct r_debug, r_map)

+               == offsetof (struct E(r_debug), r_map), "r_map");

 #endif

 static int

-E(find_maps) (pid_t pid, void *auxv, size_t auxv_size)

+E(find_maps) (const char *exe, int memfd, pid_t pid, void *auxv,

+             size_t auxv_size)

 {

   EW(Addr) phdr = 0;

   unsigned int phnum = 0;

@@ -104,12 +101,9 @@ E(find_maps) (pid_t pid, void *auxv, siz

   if (phdr == 0 || phnum == 0 || phent == 0)

     error (EXIT_FAILURE, 0, gettext ("cannot find program header of process"));

-  EW(Phdr) *p = alloca (phnum * phent);

-  if (pread64 (memfd, p, phnum * phent, phdr) != phnum * phent)

-    {

-      error (0, 0, gettext ("cannot read program header"));

-      return EXIT_FAILURE;

-    }

+  EW(Phdr) *p = xmalloc (phnum * phent);

+  if (pread (memfd, p, phnum * phent, phdr) != phnum * phent)

+    error (EXIT_FAILURE, 0, gettext ("cannot read program header"));

   /* Determine the load offset.  We need this for interpreting the

      other program header entries so we do this in a separate loop.

@@ -129,24 +123,18 @@ E(find_maps) (pid_t pid, void *auxv, siz

     if (p[i].p_type == PT_DYNAMIC)

       {

 	EW(Dyn) *dyn = xmalloc (p[i].p_filesz);

-	if (pread64 (memfd, dyn, p[i].p_filesz, offset + p[i].p_vaddr)

+       if (pread (memfd, dyn, p[i].p_filesz, offset + p[i].p_vaddr)

 	    != p[i].p_filesz)

-	  {

-	    error (0, 0, gettext ("cannot read dynamic section"));

-	    return EXIT_FAILURE;

-	  }

+         error (EXIT_FAILURE, 0, gettext ("cannot read dynamic section"));

 	/* Search for the DT_DEBUG entry.  */

 	for (unsigned int j = 0; j < p[i].p_filesz / sizeof (EW(Dyn)); ++j)

 	  if (dyn[j].d_tag == DT_DEBUG && dyn[j].d_un.d_ptr != 0)

 	    {

 	      struct E(r_debug) r;

-	      if (pread64 (memfd, &r, sizeof (r), dyn[j].d_un.d_ptr)

+             if (pread (memfd, &r, sizeof (r), dyn[j].d_un.d_ptr)

 		  != sizeof (r))

-		{

-		  error (0, 0, gettext ("cannot read r_debug"));

-		  return EXIT_FAILURE;

-		}

+               error (EXIT_FAILURE, 0, gettext ("cannot read r_debug"));

 	      if (r.r_map != 0)

 		{

@@ -160,13 +148,10 @@ E(find_maps) (pid_t pid, void *auxv, siz

       }

     else if (p[i].p_type == PT_INTERP)

       {

-	interp = alloca (p[i].p_filesz);

-	if (pread64 (memfd, interp, p[i].p_filesz, offset + p[i].p_vaddr)

+       interp = xmalloc (p[i].p_filesz);

+       if (pread (memfd, interp, p[i].p_filesz, offset + p[i].p_vaddr)

 	    != p[i].p_filesz)

-	  {

-	    error (0, 0, gettext ("cannot read program interpreter"));

-	    return EXIT_FAILURE;

-	  }

+         error (EXIT_FAILURE, 0, gettext ("cannot read program interpreter"));

       }

   if (list == 0)

@@ -174,14 +159,16 @@ E(find_maps) (pid_t pid, void *auxv, siz

       if (interp == NULL)

 	{

 	  // XXX check whether the executable itself is the loader

-	  return EXIT_FAILURE;

+         exit (EXIT_FAILURE);

 	}

       // XXX perhaps try finding ld.so and _r_debug in it

-

-      return EXIT_FAILURE;

+      exit (EXIT_FAILURE);

     }

+  free (p);

+  free (interp);

+

   /* Print the PID and program name first.  */

   printf ("%lu:\t%s\n", (unsigned long int) pid, exe);

@@ -192,47 +179,27 @@ E(find_maps) (pid_t pid, void *auxv, siz

   do

     {

       struct E(link_map) m;

-      if (pread64 (memfd, &m, sizeof (m), list) != sizeof (m))

-	{

-	  error (0, 0, gettext ("cannot read link map"));

-	  status = EXIT_FAILURE;

-	  goto out;

-	}

+      if (pread (memfd, &m, sizeof (m), list) != sizeof (m))

+       error (EXIT_FAILURE, 0, gettext ("cannot read link map"));

       EW(Addr) name_offset = m.l_name;

-    again:

       while (1)

 	{

-	  ssize_t n = pread64 (memfd, tmpbuf.data, tmpbuf.length, name_offset);

+         ssize_t n = pread (memfd, tmpbuf.data, tmpbuf.length, name_offset);

 	  if (n == -1)

-	    {

-	      error (0, 0, gettext ("cannot read object name"));

-	      status = EXIT_FAILURE;

-	      goto out;

-	    }

+           error (EXIT_FAILURE, 0, gettext ("cannot read object name"));

 	  if (memchr (tmpbuf.data, '\0', n) != NULL)

 	    break;

 	  if (!scratch_buffer_grow (&tmpbuf))

-	    {

-	      error (0, 0, gettext ("cannot allocate buffer for object name"));

-	      status = EXIT_FAILURE;

-	      goto out;

-	    }

+           error (EXIT_FAILURE, 0,

+                  gettext ("cannot allocate buffer for object name"));

 	}

-      if (((char *)tmpbuf.data)[0] == '\0' && name_offset == m.l_name

-	  && m.l_libname != 0)

-	{

-	  /* Try the l_libname element.  */

-	  struct E(libname_list) ln;

-	  if (pread64 (memfd, &ln, sizeof (ln), m.l_libname) == sizeof (ln))

-	    {

-	      name_offset = ln.name;

-	      goto again;

-	    }

-	}

+      /* The m.l_name and m.l_libname.name for loader linkmap points to same

+        values (since BZ#387 fix).  Trying to use l_libname name as the

+        shared object name might lead to an infinite loop (BZ#18035).  */

       /* Skip over the executable.  */

       if (((char *)tmpbuf.data)[0] != '\0')

@@ -242,7 +209,6 @@ E(find_maps) (pid_t pid, void *auxv, siz

     }

   while (list != 0);

- out:

   scratch_buffer_free (&tmpbuf);

   return status;

 }

diff -Nrup a/elf/tst-pldd.c b/elf/tst-pldd.c

--- a/elf/tst-pldd.c	1969-12-31 19:00:00.000000000 -0500

+++ b/elf/tst-pldd.c	2019-05-17 12:35:45.817147947 -0400

@@ -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>