From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 913A9383E83A for ; Tue, 24 May 2022 11:25:48 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 913A9383E83A Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-224-y8FcTk8MNji_E9qgGrvNUw-1; Tue, 24 May 2022 07:25:47 -0400 X-MC-Unique: y8FcTk8MNji_E9qgGrvNUw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E919F3C025C0 for ; Tue, 24 May 2022 11:25:46 +0000 (UTC) Received: from [10.97.116.14] (ovpn-116-14.gru2.redhat.com [10.97.116.14]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3EA042026D6A for ; Tue, 24 May 2022 11:25:46 +0000 (UTC) Message-ID: Date: Tue, 24 May 2022 08:25:44 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: [PINGv2] [PATCH v2] gdb/stack.c: avoid stale pointers when printing frame arguments From: Bruno Larsen To: "gdb-patches@sourceware.org" References: <20220504191036.143360-1-blarsen@redhat.com> <75aa2fe2-9ed0-83ed-e1de-4b814849707a@redhat.com> In-Reply-To: <75aa2fe2-9ed0-83ed-e1de-4b814849707a@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-11.7 required=5.0 tests=BAYES_00, BODY_8BITS, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_SHORT, RCVD_IN_DNSWL_LOW, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 24 May 2022 11:25:51 -0000 ping Cheers! Bruno Larsen On 5/18/22 08:24, Bruno Larsen wrote: > ping > > Cheers! > Bruno Larsen > > On 5/4/22 16:10, Bruno Larsen wrote: >> When a pretty printer calls an inferior function by hand, the whole >> framestack cache has to be rebuilt for that function call. However, if >> this pretty printer is called when printing the arguments of a frame, >> there are many instances where frame_info pointers were kept and end up >> stale, or used after free. This could snowball into an infinite >> recursion and GDB crash. The problem was documented as PR python/28856. >> >> To fix this problem, we must ensure that the frame cache is up to date >> after printing any arguments, so we cache the frame_id of the pointer >> that will become stale, and reset that pointer using frame_find_by_id. >> >> This commit also adds a testcase that exercises this codepath with 7 >> different triggers, run, continue, step, backtrace, finish, up and down. >> Some of them can seem to be testing the same thing twice, but since this >> test relies on stale pointers, there is always a chance that GDB got lucky >> when testing, so better to test extra. >> >> Regression tested on x86_64, using both gcc and clang. >> >> --- >> Changelog: >> v2: >>   * Addressed Tom Tromey's and Andrew's comments >>   * Added the testcase to this patch >>   * Slightly changed "finish" test, to deal better with clang >> >> --- >>   gdb/infcall.c                                 |  13 +- >>   gdb/infcmd.c                                  |   5 + >>   gdb/mi/mi-cmd-stack.c                         |   6 + >>   gdb/stack.c                                   |  31 +++- >>   .../gdb.python/pretty-print-call-by-hand.c    |  53 +++++++ >>   .../gdb.python/pretty-print-call-by-hand.exp  | 136 ++++++++++++++++++ >>   .../gdb.python/pretty-print-call-by-hand.py   |  41 ++++++ >>   7 files changed, 280 insertions(+), 5 deletions(-) >>   create mode 100644 gdb/testsuite/gdb.python/pretty-print-call-by-hand.c >>   create mode 100644 gdb/testsuite/gdb.python/pretty-print-call-by-hand.exp >>   create mode 100644 gdb/testsuite/gdb.python/pretty-print-call-by-hand.py >> >> diff --git a/gdb/infcall.c b/gdb/infcall.c >> index 5365f97049c..ad31a910da5 100644 >> --- a/gdb/infcall.c >> +++ b/gdb/infcall.c >> @@ -738,8 +738,17 @@ call_function_by_hand (struct value *function, >>                  type *default_return_type, >>                  gdb::array_view args) >>   { >> -  return call_function_by_hand_dummy (function, default_return_type, >> -                      args, NULL, NULL); >> +  scoped_restore_selected_frame restore_frame; >> +  struct value *ret = call_function_by_hand_dummy (function, >> +                           default_return_type, >> +                           args, NULL, NULL); >> +  /* Ensure that the frame cache does not contain any frames that were >> +     specific to the handmade function call.  If something is leftover >> +     while GDB has kept a reference to a frame (for instance, when a >> +     stacktrace is being printed and a pretty printed called an inferior >> +     function), GDB could crash.  */ >> +  reinit_frame_cache (); >> +  return ret; >>   } >>   /* All this stuff with a dummy frame may seem unnecessarily complicated >> diff --git a/gdb/infcmd.c b/gdb/infcmd.c >> index e909d4d4c81..380d5f0201b 100644 >> --- a/gdb/infcmd.c >> +++ b/gdb/infcmd.c >> @@ -1853,6 +1853,7 @@ finish_command (const char *arg, int from_tty) >>        source.  */ >>     if (from_tty) >>       { >> +      struct frame_id id = get_frame_id (get_selected_frame (NULL)); >>         if (execution_direction == EXEC_REVERSE) >>       gdb_printf (_("Run back to call of ")); >>         else >> @@ -1866,6 +1867,10 @@ finish_command (const char *arg, int from_tty) >>       } >>         print_stack_frame (get_selected_frame (NULL), 1, LOCATION, 0); >> +      frame = frame_find_by_id (id); >> +      if (frame == nullptr) >> +      error (_("frames disappeared mid-printing.")); >> +      frame = get_prev_frame (frame); >>       } >>     if (execution_direction == EXEC_REVERSE) >> diff --git a/gdb/mi/mi-cmd-stack.c b/gdb/mi/mi-cmd-stack.c >> index 0fe204dbc66..51c6573e9be 100644 >> --- a/gdb/mi/mi-cmd-stack.c >> +++ b/gdb/mi/mi-cmd-stack.c >> @@ -176,10 +176,16 @@ mi_cmd_stack_list_frames (const char *command, char **argv, int argc) >>          i++, fi = get_prev_frame (fi)) >>       { >>         QUIT; >> +      /* We get the frame ID here because getting it in the for line >> +         could result in getting the previous's frame ID instead.  */ >> +      struct frame_id fid = get_frame_id (fi); >>         /* Print the location and the address always, even for level 0. >>            If args is 0, don't print the arguments.  */ >>         print_frame_info (user_frame_print_options, >>                   fi, 1, LOC_AND_ADDRESS, 0 /* args */, 0); >> +      fi = frame_find_by_id (fid); >> +      if (fi == nullptr) >> +        error (_("frames disappeared mid-printing.")); >>       } >>       } >>   } >> diff --git a/gdb/stack.c b/gdb/stack.c >> index 71d85985d18..52fc8af3cb9 100644 >> --- a/gdb/stack.c >> +++ b/gdb/stack.c >> @@ -364,11 +364,19 @@ print_stack_frame (struct frame_info *frame, int print_level, >>     try >>       { >> +      /* print_frame_info may invalidate FRAME. >> +         It's better to use frame_id if we want to set the current sal.  */ >> +      struct frame_id fid = get_frame_id (frame); >>         print_frame_info (user_frame_print_options, >>               frame, print_level, print_what, 1 /* print_args */, >>               set_current_sal); >>         if (set_current_sal) >> -    set_current_sal_from_frame (frame); >> +        { >> +      frame = frame_find_by_id (fid); >> +      if (frame == nullptr) >> +          error (_("frames disappeared mid-printing.")); >> +      set_current_sal_from_frame (frame); >> +    } >>       } >>     catch (const gdb_exception_error &e) >>       { >> @@ -742,6 +750,8 @@ print_frame_args (const frame_print_options &fp_opts, >>       = (print_names >>          && fp_opts.print_frame_arguments != print_frame_arguments_none); >> +  struct frame_id printed_frame = get_frame_id (frame); >> + >>     /* Temporarily change the selected frame to the given FRAME. >>        This allows routines that rely on the selected frame instead >>        of being given a frame as parameter to use the correct frame.  */ >> @@ -902,6 +912,9 @@ print_frame_args (const frame_print_options &fp_opts, >>           } >>         first = 0; >> +      frame = frame_find_by_id (printed_frame); >> +      if (frame == nullptr) >> +        error (_("frames disappeared mid-printing.")); >>       } >>       } >> @@ -1109,12 +1122,21 @@ print_frame_info (const frame_print_options &fp_opts, >>        to get the line containing FRAME->pc.  */ >>     symtab_and_line sal = find_frame_sal (frame); >> +  /* print_frame can invalidate frame, so cache the frame_id to rebuild >> +     the whole stack later, if needed.  */ >> +  struct frame_id frame_id = get_frame_id (frame); >> + >>     location_print = (print_what == LOCATION >>               || print_what == SRC_AND_LOC >>               || print_what == LOC_AND_ADDRESS >>               || print_what == SHORT_LOCATION); >>     if (location_print || !sal.symtab) >> -    print_frame (fp_opts, frame, print_level, print_what, print_args, sal); >> +    { >> +      print_frame (fp_opts, frame, print_level, print_what, print_args, sal); >> +      frame = frame_find_by_id (frame_id); >> +      if (frame == nullptr) >> +      error (_("frames disappeared mid-printing.")); >> +    } >>     source_print = (print_what == SRC_LINE || print_what == SRC_AND_LOC); >> @@ -2060,6 +2082,7 @@ backtrace_command_1 (const frame_print_options &fp_opts, >>         for (fi = trailing; fi && count--; fi = get_prev_frame (fi)) >>       { >>         QUIT; >> +      struct frame_id frame_id = get_frame_id (fi); >>         /* Don't use print_stack_frame; if an error() occurs it probably >>            means further attempts to backtrace would fail (on the other >> @@ -2067,9 +2090,11 @@ backtrace_command_1 (const frame_print_options &fp_opts, >>            the frame->prev field gets set to NULL in that case).  */ >>         print_frame_info (fp_opts, fi, 1, LOCATION, 1, 0); >> +      fi = frame_find_by_id (frame_id); >> +      if (fi == nullptr) >> +        error (_("frames disappeared mid-printing.")); >>         if ((flags & PRINT_LOCALS) != 0) >>           { >> -          struct frame_id frame_id = get_frame_id (fi); >>             print_frame_local_vars (fi, false, NULL, NULL, 1, gdb_stdout); >> diff --git a/gdb/testsuite/gdb.python/pretty-print-call-by-hand.c b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.c >> new file mode 100644 >> index 00000000000..3be5675b096 >> --- /dev/null >> +++ b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.c >> @@ -0,0 +1,53 @@ >> +/* This testcase is part of GDB, the GNU debugger. >> + >> +   Copyright 2022 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  .  */ >> + >> +struct mytype >> +{ >> +  char *x; >> +}; >> + >> +void >> +rec (int i) >> +{ >> +  if (i <= 0) >> +    return; >> +  rec (i-1); >> +} >> + >> +int >> +f () >> +{ >> +  rec (100); >> +  return 2; >> +} >> + >> +void >> +g (struct mytype mt, int depth) >> +{ >> +  if (depth <= 0) >> +    return; /* TAG: final frame */ >> +  g (mt, depth - 1); /* TAG: first frame */ >> +} >> + >> +int >> +main () >> +{ >> +  struct mytype mt; >> +  mt.x = "hello world"; >> +  g (mt, 10); /* TAG: outside the frame */ >> +  return 0; >> +} >> diff --git a/gdb/testsuite/gdb.python/pretty-print-call-by-hand.exp b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.exp >> new file mode 100644 >> index 00000000000..0aeb2218f91 >> --- /dev/null >> +++ b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.exp >> @@ -0,0 +1,136 @@ >> +# Copyright (C) 2022 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 . >> + >> +# This file is part of the GDB testsuite.  It tests a pretty printer that >> +# calls an inferior function by hand, triggering a Use-after-Free bug >> +# (PR gdb/28856). >> + >> +load_lib gdb-python.exp >> + >> +standard_testfile >> + >> +# gdb needs to be started here for skip_python_tests to work. >> +# prepare_for_testing could be used instead, but it could compile the program >> +# unnecessarily, so starting GDB like this is preferable. >> +gdb_start >> + >> +# Skip all tests if Python scripting is not enabled. >> +if { [skip_python_tests] } { continue } >> + >> +if { [prepare_for_testing "failed to prepare" $testfile $srcfile debug] } { >> +    untested "failed to compile" >> +    return -1 >> +} >> + >> +# This proc restarts GDB, makes the inferior reach the desired spot - marked >> +# by a comment in the .c file - and turns on the pretty printer for testing. >> +# Starting with a new GDB is important because the test may crash GDB.  The >> +# return values are here to avoid us trying to test the pretty printer if >> +# there was a problem getting to main. >> +proc start_test { breakpoint_comment } { >> +    global srcdir subdir testfile binfile >> + >> +    # Start with a fresh gdb. >> +    # This is important because the test can crash GDB. >> + >> +    clean_restart ${binfile} >> + >> +    if { ![runto_main] } then { >> +    untested "couldn't run to breakpoint" >> +    return -1 >> +    } >> + >> +    # Let GDB get to the return line. >> +    gdb_breakpoint [gdb_get_line_number ${breakpoint_comment} ${testfile}.c ] >> +    gdb_continue_to_breakpoint ${breakpoint_comment} ".*" >> + >> +    gdb_test_no_output "set print pretty on" "starting to pretty print" >> + >> +    set remote_python_file [gdb_remote_download host ${srcdir}/${subdir}/${testfile}.py] >> +    gdb_test_no_output "source ${remote_python_file}" "load python file" >> + >> +    return 0 >> +} >> + >> +# Start by testing the "run" command, it can't leverage start_test >> +with_test_prefix "run to frame" { >> +    if { ![runto_main] } then { >> +    untested "couldn't run to main" >> +    } >> + >> +    gdb_test_no_output "set print pretty on" "starting to pretty print" >> + >> +    set remote_python_file [gdb_remote_download host ${srcdir}/${subdir}/${testfile}.py] >> +    gdb_test_no_output "source ${remote_python_file}" "load python file" >> + >> +    gdb_breakpoint [gdb_get_line_number "TAG: final frame" ${testfile}.c] >> +    gdb_continue_to_breakpoint "TAG: final frame" ".*" >> +} >> + >> +# Testing the backtrace command. >> +with_test_prefix "frame print" { >> +    if { [start_test "TAG: final frame"] == 0 } { >> +    gdb_test "backtrace -frame-arguments all" [multi_line \ >> +    "#0 .*g \\(mt=mytype is .*\\, depth=0\\).*"\ >> +    "#1 .*g \\(mt=mytype is .*\\, depth=1\\).*"\ >> +    "#2 .*g \\(mt=mytype is .*\\, depth=2\\).*"\ >> +    "#3 .*g \\(mt=mytype is .*\\, depth=3\\).*"\ >> +    "#4 .*g \\(mt=mytype is .*\\, depth=4\\).*"\ >> +    "#5 .*g \\(mt=mytype is .*\\, depth=5\\).*"\ >> +    "#6 .*g \\(mt=mytype is .*\\, depth=6\\).*"\ >> +    "#7 .*g \\(mt=mytype is .*\\, depth=7\\).*"\ >> +    "#8 .*g \\(mt=mytype is .*\\, depth=8\\).*"\ >> +    "#9 .*g \\(mt=mytype is .*\\, depth=9\\).*"\ >> +    "#10 .*g \\(mt=mytype is .*\\, depth=10\\).*"\ >> +    "#11 .*main \\(\\).*"] \ >> +    "backtrace test" >> +    } >> +} >> +# Testing the down command. >> +with_test_prefix "frame movement down" { >> +    if { [start_test "TAG: first frame"] == 0 } { >> +    gdb_test "up" [multi_line "#1 .*in main \\(\\) at .*" ".*outside the frame.*"] >> +    gdb_test "down" [multi_line "#0\\s+g \\(mt=mytype is .*\\, depth=10\\).*" ".*first frame.*"] >> +    } >> +} >> + >> +# Testing the up command. >> +with_test_prefix "frame movement up" { >> +    if { [start_test "TAG: final frame"] == 0 } { >> +    gdb_test "up" [multi_line "#1 .*in g \\(mt=mytype is .*\\, depth=1\\).*" ".*first frame.*"] >> +    } >> +} >> + >> +# Testing the finish command. >> +with_test_prefix "frame exit through finish" { >> +    if { [start_test "TAG: final frame"] == 0 } { >> +    gdb_test "finish" [multi_line ".*.*g \\(mt=mytype is .*\\, depth=0\\).*" ".*g \\(mt=mytype is .*\\, depth=1\\).*" ".*"] >> +    } >> +} >> + >> +# Testing the step command. >> +with_test_prefix "frame enter through step" { >> +    if { [start_test "TAG: outside the frame"] == 0 } { >> +    gdb_test "step" [multi_line "g \\(mt=mytype is .*\\, depth=10\\).*" "41.*if \\(depth \\<= 0\\)"] >> +    } >> +} >> + >> +# Testing the continue command. >> +with_test_prefix "frame enter through continue" { >> +    if { [start_test "TAG: outside the frame"] == 0 } { >> +    gdb_breakpoint [gdb_get_line_number "TAG: first frame" ${testfile}.c ] >> +    gdb_continue_to_breakpoint "TAG: first frame" ".*TAG: first frame.*" >> +    } >> +} >> diff --git a/gdb/testsuite/gdb.python/pretty-print-call-by-hand.py b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.py >> new file mode 100644 >> index 00000000000..f8f5df678f8 >> --- /dev/null >> +++ b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.py >> @@ -0,0 +1,41 @@ >> +# Copyright (C) 2022 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 . >> + >> + >> +class MytypePrinter: >> +    """pretty print my type""" >> + >> +    def __init__(self, val): >> +        self.val = val >> + >> +    def to_string(self): >> +        calls = gdb.parse_and_eval('f()') >> +        return "mytype is %s" % self.val['x'] >> + >> +def ec_lookup_function(val): >> +    typ = val.type >> +    if typ.code == gdb.TYPE_CODE_REF: >> +        typ = typ.target() >> +    if str(typ) == 'struct mytype': >> +        return MytypePrinter(val) >> +    return None >> + >> +def disable_lookup_function(): >> +    ec_lookup_function.enabled = False >> + >> +def enable_lookup_function(): >> +    ec_lookup_function.enabled = True >> + >> +gdb.pretty_printers.append(ec_lookup_function)