[Bug gdb/23613] gdb segfaults when in an unreachable directory

cvs-commit at gcc dot gnu.org sourceware-bugzilla@sourceware.org
Sat Dec 14 04:51:00 GMT 2019


--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Sergio Durigan Junior


commit ff8577f64987a898e1dc5eb6afb66a404fb7bb16
Author: Sergio Durigan Junior <sergiodj@redhat.com>
Date:   Wed Jul 10 16:18:27 2019 -0400

    Guard against 'current_directory == NULL' on gdb_abspath (PR gdb/23613)

    Ref.: https://bugzilla.redhat.com/show_bug.cgi?id=1728147
    Ref.: https://sourceware.org/bugzilla/show_bug.cgi?id=23613


    This bug has been reported against Fedora GDB, but there's also an
    upstream bug.  The problem reported is that GDB segfaults when the
    working directory is deleted.  It's pretty use to reproduce it:

      mkdir bla
      cd bla
      rmdir ../bla
      gdb echo

    Debugging the problem is a bit tricky, because, since the current
    directory doesn't exist anymore, a corefile cannot be saved there.
    After a few attempts, I came up with the following:

      gdb -ex 'shell mkdir bla' -ex 'cd bla' -ex 'shell rmdir ../bla' -ex 'r
echo' ./gdb/gdb

    This assumes that you're inside a build directory which contains
    ./gdb/gdb, of course.

    After investigating it, I found that the problem happens at
    gdb_abspath, where we're dereferencing 'current_directory' without
    checking if it's NULL:

        (concat (current_directory,
             IS_DIR_SEPARATOR (current_directory[strlen (current_directory) -
             ? "" : SLASH_STRING,

    So I fixed the problem with the patch below.  The idea is that, if
    'current_directory' is NULL, then the final string returned should be
    just the "path".

    After fixing the bug, I found a similar one reported against our
    bugzilla: PR gdb/23613.  The problem is the same, but the reproducer
    is a bit different.

    I really tried writing a testcase for this, but unfortunately it's
    apparently not possible to start GDB inside a non-existent directory
    with DejaGNU.

    I regression tested this patch on the BuildBot, and no regressions
    were found.

    2019-12-14  Sergio Durigan Junior  <sergiodj@redhat.com>

        PR gdb/23613
        * bsd-kvm.c (bsd_kvm_target_open): Use 'gdb_abspath'.
        * corelow.c: Include 'gdbsupport/pathstuff.h'.
        (core_target_open): Use 'gdb_abspath'.
        * gdbsupport/pathstuff.c (gdb_abspath): Guard against
        'current_directory == NULL' case.
        * gdbsupport/pathstuff.h (gdb_abspath): Expand comment and
        explain what happens when 'current_directory' is NULL.
        * go32-nat.c (go32_nat_target::wait): Check if
        'current_directory' is NULL before call to 'chdir'.
        * source.c (add_path): Use 'gdb_abspath'.
        * top.c: Include 'gdbsupport/pathstuff.h'.
        (init_history): Use 'gdb_abspath'.
        (set_history_filename): Likewise.
        * tracefile-tfile.c: Include 'gdbsupport/pathstuff.h'.
        (tfile_target_open): Use 'gdb_abspath'.

    Change-Id: Ibb0932fa25bc5c2d3ae4a7f64bd7f32885ca403b

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