From ff8577f64987a898e1dc5eb6afb66a404fb7bb16 Mon Sep 17 00:00:00 2001 From: Sergio Durigan Junior Date: Wed, 10 Jul 2019 16:18:27 -0400 Subject: 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 Hi, 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) - 1]) ? "" : 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. gdb/ChangeLog: 2019-12-14 Sergio Durigan Junior https://bugzilla.redhat.com/show_bug.cgi?id=1728147 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 --- gdb/top.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) (limited to 'gdb/top.c') diff --git a/gdb/top.c b/gdb/top.c index e8ed3b2..bc300e4 100644 --- a/gdb/top.c +++ b/gdb/top.c @@ -54,6 +54,7 @@ #include "gdb_select.h" #include "gdbsupport/scope-exit.h" #include "gdbarch.h" +#include "gdbsupport/pathstuff.h" /* readline include files. */ #include "readline/readline.h" @@ -1994,12 +1995,13 @@ init_history (void) that was read. */ #ifdef __MSDOS__ /* No leading dots in file names are allowed on MSDOS. */ - history_filename = concat (current_directory, "/_gdb_history", - (char *)NULL); + const char *fname = "_gdb_history"; #else - history_filename = concat (current_directory, "/.gdb_history", - (char *)NULL); + const char *fname = ".gdb_history"; #endif + + gdb::unique_xmalloc_ptr temp (gdb_abspath (fname)); + history_filename = temp.release (); } read_history (history_filename); } @@ -2077,8 +2079,12 @@ set_history_filename (const char *args, directories the file written will be the same as the one that was read. */ if (!IS_ABSOLUTE_PATH (history_filename)) - history_filename = reconcat (history_filename, current_directory, "/", - history_filename, (char *) NULL); + { + gdb::unique_xmalloc_ptr temp (gdb_abspath (history_filename)); + + xfree (history_filename); + history_filename = temp.release (); + } } static void -- cgit v1.1