Re: [RFC] Detect loops in the solib chain

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

On Fri, 09 Apr 2010 17:41:23 +0200, Jan Kratochvil wrote:
> On Sat, 19 Jul 2008 01:02:10 +0200, Kevin Buettner wrote:
> > It seems to me that the ldsomap check could be avoided if you were to
> > set prev_lm to 0 just after ldsomap gets set.  (It's been a while
> > since I've checked, but I'm guessing that in the case of a unattached
> > dynamic linker entry, you'd expect both LM_NEXT and LM_PREV for that
> > entry to be zero.)
> 
> Not done.  It has a risk of regression on Solaris, I do not have Solaris
> easily available (OK, to boot a VM) and keeping the patch as is just does not
> apply the new sanity check on the Solaris specific ld.so single entry list.

Done this part this time.  It works during basic test but it is not regression
tested on Solaris as system expect + custom dejagnu produce \r\r\n EOLs
breaking the testsuite completely.


Thanks,
Jan


gdb/
2010-04-09  Daniel Jacobowitz  <dan@codesourcery.com>
	    Paul Pluzhnikov  <ppluzhnikov@google.com>
	    Jan Kratochvil  <jan.kratochvil@redhat.com>

	Fix deadlock on looped list of loaded shared objects.
	* solib-svr4.c (LM_PREV): New function.
	(IGNORE_FIRST_LINK_MAP_ENTRY): Use it.
	(svr4_current_sos): Check for correct l_prev.  New variables prev_lm
	and next_lm.  Clear prev_lm for solib_svr4_r_ldsomap.
	* config/djgpp/fnchange.lst: Add translation for solib-corrupted.exp.

gdb/testsuite/
2010-04-09  Jan Kratochvil  <jan.kratochvil@redhat.com>

	Fix deadlock on looped list of loaded shared objects.
	* gdb.base/solib-corrupted.exp: New.

--- a/gdb/config/djgpp/fnchange.lst
+++ b/gdb/config/djgpp/fnchange.lst
@@ -397,6 +397,7 @@
 @V@/gdb/testsuite/gdb.base/siginfo-obj.c @V@/gdb/testsuite/gdb.base/si-obj.c
 @V@/gdb/testsuite/gdb.base/siginfo-addr.exp @V@/gdb/testsuite/gdb.base/si-addr.exp
 @V@/gdb/testsuite/gdb.base/siginfo-obj.exp @V@/gdb/testsuite/gdb.base/si-obj.exp
+@V@/gdb/testsuite/gdb.base/solib-corrupted.exp @V@/gdb/testsuite/gdb.base/so-crptd.exp
 @V@/gdb/testsuite/gdb.base/solib-disc.c @V@/gdb/testsuite/gdb.base/so-disc.c
 @V@/gdb/testsuite/gdb.base/solib-display-lib.c @V@/gdb/testsuite/gdb.base/so-displib.c
 @V@/gdb/testsuite/gdb.base/solib-display-main.c @V@/gdb/testsuite/gdb.base/so-dispmain.c
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -272,6 +272,16 @@ LM_NEXT (struct so_list *so)
 }
 
 static CORE_ADDR
+LM_PREV (struct so_list *so)
+{
+  struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
+  struct type *ptr_type = builtin_type (target_gdbarch)->builtin_data_ptr;
+
+  return extract_typed_address (so->lm_info->lm + lmo->l_prev_offset,
+				ptr_type);
+}
+
+static CORE_ADDR
 LM_NAME (struct so_list *so)
 {
   struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
@@ -284,16 +294,12 @@ LM_NAME (struct so_list *so)
 static int
 IGNORE_FIRST_LINK_MAP_ENTRY (struct so_list *so)
 {
-  struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
-  struct type *ptr_type = builtin_type (target_gdbarch)->builtin_data_ptr;
-
   /* Assume that everything is a library if the dynamic loader was loaded
      late by a static executable.  */
   if (exec_bfd && bfd_get_section_by_name (exec_bfd, ".dynamic") == NULL)
     return 0;
 
-  return extract_typed_address (so->lm_info->lm + lmo->l_prev_offset,
-				ptr_type) == 0;
+  return LM_PREV (so) == 0;
 }
 
 /* Per pspace SVR4 specific data.  */
@@ -1101,7 +1107,7 @@ svr4_default_sos (void)
 static struct so_list *
 svr4_current_sos (void)
 {
-  CORE_ADDR lm;
+  CORE_ADDR lm, prev_lm;
   struct so_list *head = 0;
   struct so_list **link_ptr = &head;
   CORE_ADDR ldsomap = 0;
@@ -1120,6 +1126,7 @@ svr4_current_sos (void)
 
   /* Walk the inferior's link map list, and build our list of
      `struct so_list' nodes.  */
+  prev_lm = 0;
   lm = solib_svr4_r_map (info);
 
   while (lm)
@@ -1127,6 +1134,7 @@ svr4_current_sos (void)
       struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
       struct so_list *new = XZALLOC (struct so_list);
       struct cleanup *old_chain = make_cleanup (xfree, new);
+      CORE_ADDR next_lm;
 
       new->lm_info = xmalloc (sizeof (struct lm_info));
       make_cleanup (xfree, new->lm_info);
@@ -1138,14 +1146,21 @@ svr4_current_sos (void)
 
       read_memory (lm, new->lm_info->lm, lmo->link_map_size);
 
-      lm = LM_NEXT (new);
+      next_lm = LM_NEXT (new);
+
+      if (LM_PREV (new) != prev_lm)
+	{
+	  warning (_("Corrupted shared library list"));
+	  free_so (new);
+	  next_lm = 0;
+	}
 
       /* For SVR4 versions, the first entry in the link map is for the
          inferior executable, so we must ignore it.  For some versions of
          SVR4, it has no name.  For others (Solaris 2.3 for example), it
          does have a name, so we can no longer use a missing name to
          decide when to ignore it. */
-      if (IGNORE_FIRST_LINK_MAP_ENTRY (new) && ldsomap == 0)
+      else if (IGNORE_FIRST_LINK_MAP_ENTRY (new) && ldsomap == 0)
 	{
 	  info->main_lm_addr = new->lm_info->lm_addr;
 	  free_so (new);
@@ -1182,12 +1197,18 @@ svr4_current_sos (void)
 	    }
 	}
 
+      prev_lm = lm;
+      lm = next_lm;
+
       /* On Solaris, the dynamic linker is not in the normal list of
 	 shared objects, so make sure we pick it up too.  Having
 	 symbol information for the dynamic linker is quite crucial
 	 for skipping dynamic linker resolver code.  */
       if (lm == 0 && ldsomap == 0)
-	lm = ldsomap = solib_svr4_r_ldsomap (info);
+	{
+	  lm = ldsomap = solib_svr4_r_ldsomap (info);
+	  prev_lm = 0;
+	}
 
       discard_cleanups (old_chain);
     }
--- /dev/null
+++ b/gdb/testsuite/gdb.base/solib-corrupted.exp
@@ -0,0 +1,45 @@
+# Copyright 2010 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+set testfile "solib-corrupted"
+set srcfile start.c
+
+if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile}] } {
+    untested ${testfile}.exp
+    return -1
+}
+
+if ![runto_main] {
+    fail "Can't run to main"
+    return
+}
+
+gdb_test "info sharedlibrary" "" "normal list"
+
+# GDB checks there for matching L_PREV.
+set test "make solibs looping"
+gdb_test_multiple "p/x _r_debug->r_map->l_next = _r_debug->r_map" $test {
+    -re "(No symbol \"_r_debug\" in current context\\.|Attempt to extract a component of a value that is not a structure pointer\\.)\r\n$gdb_prompt $" {
+	# glibc debug info is not available and it is too difficult to find and
+	# parse it from this testcase without the gdb supporting functions.
+	xfail "$test (no _r_debug symbol)"
+	untested ${testfile}.exp
+	return
+    }
+    -re " = 0x\[0-9a-f\]+\r\n$gdb_prompt $" {
+	pass $test
+    }
+}
+gdb_test "info sharedlibrary" "warning: Corrupted shared library list\r\n.*" "corrupted list"