[Bug exp/31258] [gdb] ThreadSanitizer: heap-use-after-free in memmove

["cvs-commit at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31258

--- Comment #6 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom de Vries <vries@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=c3e06e640e53afa75d82b44f4b701815be3db19b

commit c3e06e640e53afa75d82b44f4b701815be3db19b
Author: Tom de Vries <tdevries@suse.de>
Date:   Mon Feb 19 09:59:15 2024 +0100

    [gdb/exp] Fix printing of out of bounds struct members

    When building gdb with -O0 -fsanitize=address, and running test-case
    gdb.ada/uninitialized_vars.exp, I run into:
    ...
    (gdb) info locals
    a = 0
    z = (a => 1, b => false, c => 2.0)
    =================================================================
    ==66372==ERROR: AddressSanitizer: heap-buffer-overflow on address
0x602000097f58 at pc 0xffff52c0da1c bp 0xffffc90a1d40 sp 0xffffc90a1d80
    READ of size 4 at 0x602000097f58 thread T0
        #0 0xffff52c0da18 in memmove (/lib64/libasan.so.8+0x6da18)
        #1 0xbcab24 in unsigned char* std::__copy_move_backward<false, true,
std::random_access_iterator_tag>::__copy_move_b<unsigned char const, unsigned
char>(unsigned char const*, unsigned char const*, unsigned char*)
/usr/include/c++/13/bits/stl_algobase.h:748
        #2 0xbc9bf4 in unsigned char* std::__copy_move_backward_a2<false,
unsigned char const*, unsigned char*>(unsigned char const*, unsigned char
const*, unsigned char*) /usr/include/c++/13/bits/stl_algobase.h:769
        #3 0xbc898c in unsigned char* std::__copy_move_backward_a1<false,
unsigned char const*, unsigned char*>(unsigned char const*, unsigned char
const*, unsigned char*) /usr/include/c++/13/bits/stl_algobase.h:778
        #4 0xbc715c in unsigned char* std::__copy_move_backward_a<false,
unsigned char const*, unsigned char*>(unsigned char const*, unsigned char
const*, unsigned char*) /usr/include/c++/13/bits/stl_algobase.h:807
        #5 0xbc4e6c in unsigned char* std::copy_backward<unsigned char const*,
unsigned char*>(unsigned char const*, unsigned char const*, unsigned char*)
/usr/include/c++/13/bits/stl_algobase.h:867
        #6 0xbc2934 in void gdb::copy<unsigned char const, unsigned
char>(gdb::array_view<unsigned char const>, gdb::array_view<unsigned char>)
gdb/../gdbsupport/array-view.h:223
        #7 0x20e0100 in value::contents_copy_raw(value*, long, long, long)
gdb/value.c:1239
        #8 0x20e9830 in value::primitive_field(long, int, type*)
gdb/value.c:3078
        #9 0x20e98f8 in value_field(value*, int) gdb/value.c:3095
        #10 0xcafd64 in print_field_values gdb/ada-valprint.c:658
        #11 0xcb0fa0 in ada_val_print_struct_union gdb/ada-valprint.c:857
        #12 0xcb1bb4 in ada_value_print_inner(value*, ui_file*, int,
value_print_options const*) gdb/ada-valprint.c:1042
        #13 0xc66e04 in ada_language::value_print_inner(value*, ui_file*, int,
value_print_options const*) const (/home/vries/gdb/build/gdb/gdb+0xc66e04)
        #14 0x20ca1e8 in common_val_print(value*, ui_file*, int,
value_print_options const*, language_defn const*) gdb/valprint.c:1092
        #15 0x20caabc in common_val_print_checked(value*, ui_file*, int,
value_print_options const*, language_defn const*) gdb/valprint.c:1184
        #16 0x196c524 in print_variable_and_value(char const*, symbol*,
frame_info_ptr, ui_file*, int) gdb/printcmd.c:2355
        #17 0x1d99ca0 in print_variable_and_value_data::operator()(char const*,
symbol*) gdb/stack.c:2308
        #18 0x1dabca0 in gdb::function_view<void (char const*,
symbol*)>::bind<print_variable_and_value_data>(print_variable_and_value_data&)::{lambda(gdb::fv_detail::erased_callable,
char const*, symbol*)#1}::operator()(gdb::fv_detail::erased_callable, char
const*, symbol*) const gdb/../gdbsupport/function-view.h:305
        #19 0x1dabd14 in gdb::function_view<void (char const*,
symbol*)>::bind<print_variable_and_value_data>(print_variable_and_value_data&)::{lambda(gdb::fv_detail::erased_callable,
char const*, symbol*)#1}::_FUN(gdb::fv_detail::erased_callable, char const*,
symbol*) gdb/../gdbsupport/function-view.h:299
        #20 0x1dab34c in gdb::function_view<void (char const*,
symbol*)>::operator()(char const*, symbol*) const
gdb/../gdbsupport/function-view.h:289
        #21 0x1d9963c in iterate_over_block_locals gdb/stack.c:2240
        #22 0x1d99790 in iterate_over_block_local_vars(block const*,
gdb::function_view<void (char const*, symbol*)>) gdb/stack.c:2259
        #23 0x1d9a598 in print_frame_local_vars gdb/stack.c:2380
        #24 0x1d9afac in info_locals_command(char const*, int) gdb/stack.c:2458
        #25 0xfd7b30 in do_simple_func gdb/cli/cli-decode.c:95
        #26 0xfe5a2c in cmd_func(cmd_list_element*, char const*, int)
gdb/cli/cli-decode.c:2735
        #27 0x1f03790 in execute_command(char const*, int) gdb/top.c:575
        #28 0x1384080 in command_handler(char const*) gdb/event-top.c:566
        #29 0x1384e2c in command_line_handler(std::unique_ptr<char,
gdb::xfree_deleter<char> >&&) gdb/event-top.c:802
        #30 0x1f731e4 in tui_command_line_handler gdb/tui/tui-interp.c:104
        #31 0x1382a58 in gdb_rl_callback_handler gdb/event-top.c:259
        #32 0x21dbb80 in rl_callback_read_char readline/readline/callback.c:290
        #33 0x1382510 in gdb_rl_callback_read_char_wrapper_noexcept
gdb/event-top.c:195
        #34 0x138277c in gdb_rl_callback_read_char_wrapper gdb/event-top.c:234
        #35 0x1fe9b40 in stdin_event_handler gdb/ui.c:155
        #36 0x35ff1bc in handle_file_event gdbsupport/event-loop.cc:573
        #37 0x35ff9d8 in gdb_wait_for_event gdbsupport/event-loop.cc:694
        #38 0x35fd284 in gdb_do_one_event(int) gdbsupport/event-loop.cc:264
        #39 0x1768080 in start_event_loop gdb/main.c:408
        #40 0x17684c4 in captured_command_loop gdb/main.c:472
        #41 0x176cfc8 in captured_main gdb/main.c:1342
        #42 0x176d088 in gdb_main(captured_main_args*) gdb/main.c:1361
        #43 0xb73edc in main gdb/gdb.c:39
        #44 0xffff519b09d8 in __libc_start_call_main (/lib64/libc.so.6+0x309d8)
        #45 0xffff519b0aac in __libc_start_main@@GLIBC_2.34
(/lib64/libc.so.6+0x30aac)
        #46 0xb73c2c in _start (/home/vries/gdb/build/gdb/gdb+0xb73c2c)

    0x602000097f58 is located 0 bytes after 8-byte region
[0x602000097f50,0x602000097f58)
    allocated by thread T0 here:
        #0 0xffff52c65218 in calloc (/lib64/libasan.so.8+0xc5218)
        #1 0xcbc278 in xcalloc gdb/alloc.c:97
        #2 0x35f21e8 in xzalloc(unsigned long) gdbsupport/common-utils.cc:29
        #3 0x20de270 in value::allocate_contents(bool) gdb/value.c:937
        #4 0x20edc08 in value::fetch_lazy() gdb/value.c:4033
        #5 0x20dadc0 in
value::entirely_covered_by_range_vector(std::vector<range,
std::allocator<range> > const&) gdb/value.c:229
        #6 0xcb2298 in value::entirely_optimized_out() gdb/value.h:560
        #7 0x20ca6fc in value_check_printable gdb/valprint.c:1133
        #8 0x20caa8c in common_val_print_checked(value*, ui_file*, int,
value_print_options const*, language_defn const*) gdb/valprint.c:1182
        #9 0x196c524 in print_variable_and_value(char const*, symbol*,
frame_info_ptr, ui_file*, int) gdb/printcmd.c:2355
        #10 0x1d99ca0 in print_variable_and_value_data::operator()(char const*,
symbol*) gdb/stack.c:2308
        #11 0x1dabca0 in gdb::function_view<void (char const*,
symbol*)>::bind<print_variable_and_value_data>(print_variable_and_value_data&)::{lambda(gdb::fv_detail::erased_callable,
char const*, symbol*)#1}::operator()(gdb::fv_detail::erased_callable, char
const*, symbol*) const gdb/../gdbsupport/function-view.h:305
        #12 0x1dabd14 in gdb::function_view<void (char const*,
symbol*)>::bind<print_variable_and_value_data>(print_variable_and_value_data&)::{lambda(gdb::fv_detail::erased_callable,
char const*, symbol*)#1}::_FUN(gdb::fv_detail::erased_callable, char const*,
symbol*) gdb/../gdbsupport/function-view.h:299
        #13 0x1dab34c in gdb::function_view<void (char const*,
symbol*)>::operator()(char const*, symbol*) const
gdb/../gdbsupport/function-view.h:289
        #14 0x1d9963c in iterate_over_block_locals gdb/stack.c:2240
        #15 0x1d99790 in iterate_over_block_local_vars(block const*,
gdb::function_view<void (char const*, symbol*)>) gdb/stack.c:2259
        #16 0x1d9a598 in print_frame_local_vars gdb/stack.c:2380
        #17 0x1d9afac in info_locals_command(char const*, int) gdb/stack.c:2458
        #18 0xfd7b30 in do_simple_func gdb/cli/cli-decode.c:95
        #19 0xfe5a2c in cmd_func(cmd_list_element*, char const*, int)
gdb/cli/cli-decode.c:2735
        #20 0x1f03790 in execute_command(char const*, int) gdb/top.c:575
        #21 0x1384080 in command_handler(char const*) gdb/event-top.c:566
        #22 0x1384e2c in command_line_handler(std::unique_ptr<char,
gdb::xfree_deleter<char> >&&) gdb/event-top.c:802
        #23 0x1f731e4 in tui_command_line_handler gdb/tui/tui-interp.c:104
        #24 0x1382a58 in gdb_rl_callback_handler gdb/event-top.c:259
        #25 0x21dbb80 in rl_callback_read_char readline/readline/callback.c:290
        #26 0x1382510 in gdb_rl_callback_read_char_wrapper_noexcept
gdb/event-top.c:195
        #27 0x138277c in gdb_rl_callback_read_char_wrapper gdb/event-top.c:234
        #28 0x1fe9b40 in stdin_event_handler gdb/ui.c:155
        #29 0x35ff1bc in handle_file_event gdbsupport/event-loop.cc:573

    SUMMARY: AddressSanitizer: heap-buffer-overflow
(/lib64/libasan.so.8+0x6da18) in memmove
    ...

    The error happens when trying to print either variable y or y2:
    ...
       type Variable_Record (A : Boolean := True) is record
          case A is
             when True =>
                B : Integer;
             when False =>
                C : Float;
                D : Integer;
          end case;
       end record;
       Y  : Variable_Record := (A => True, B => 1);
       Y2 : Variable_Record := (A => False, C => 1.0, D => 2);
    ...
    when the variables are uninitialized.

    The error happens only when printing the entire variable:
    ...
    (gdb) p y.a
    $2 = 216
    (gdb) p y.b
    There is no member named b.
    (gdb) p y.c
    $3 = 9.18340949e-41
    (gdb) p y.d
    $4 = 1
    (gdb) p y
    <AddressSanitizer: heap-buffer-overflow>
    ...

    The error happens as follows:
    - field a functions as discriminant, choosing either the b, or c+d variant.
    - when y.a happens to be set to 216, as above, gdb interprets this as the
      variable having the c+d variant (which is why trying to print y.b fails).
    - when printing y, gdb allocates a value, copies the bytes into it from the
      target, and then prints the value.
    - gdb allocates the value using the type size, which is 8.  It's 8 because
      that's what the DW_AT_byte_size indicates.  Note that for valid values of
a,
      it gives correct results: if a is 0 (c+d variant), size is 12, if a is 1
      (b variant), size is 8.
    - gdb tries to print field d, which is at an 8 byte offset, and that
results
      in a out-of-bounds access for the allocated 8-byte value.

    Fix this by handling this case in value::contents_copy_raw, such that we
have:
    ...
    (gdb) p y
    $1 = (a => 24, c => 9.18340949e-41,
          d => <error reading variable: access outside bounds of object>)
    ...

    An alternative (additional) fix could be this: in
compute_variant_fields_inner
    gdb reads the discriminant y.a to decide which variant is active.  It would
be
    nice to detect that the value (y.a == 24) is not a valid Boolean, and give
up
    on choosing a variant altoghether.  However, the situation regarding the
    internal type CODE_TYPE_BOOL is currently ambiguous (see PR31282) and it's
not
    possible to reliably decide what valid values are.

    The test-case source file gdb.ada/uninitialized-variable-record/parse.adb
is
    a reduced version of gdb.ada/uninitialized_vars/parse.adb, so it copies the
    copyright years.

    Note that the test-case needs gcc-12 or newer, it's unsupported for older
gcc
    versions. [ So, it would be nice to rewrite it into a dwarf assembly
    test-case. ]

    The test-case loops over all languages.  This is inherited from an earlier
    attempt to fix this, which had language-specific fixes (in
print_field_values,
    cp_print_value_fields, pascal_object_print_value_fields and
    f_language::value_print_inner).  I've left this in, but I suppose it's not
    strictly necessary anymore.

    Tested on x86_64-linux.

    PR exp/31258
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31258

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