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f8631e5e04
[I sent this earlier today, but I don't see it in the archives.
Resending it through a different computer / SMTP.]
The use of the static buffer in command_line_input is becoming
problematic, as explained here [1]. In short, with this patch [2] that
attempt to fix a post-hook bug, when running gdb.base/commands.exp, we
hit a case where we read a "define" command line from a script file
using command_command_line_input. The command line is stored in
command_line_input's static buffer. Inside the define command's
execution, we read the lines inside the define using command_line_input,
which overwrites the define command, in command_line_input's static
buffer. After the execution of the define command, execute_command does
a command look up to see if a post-hook is registered. For that, it
uses a now stale pointer that used to point to the define command, in
the static buffer, causing a use-after-free. Note that the pointer in
execute_command points to the dynamically-allocated buffer help by the
static buffer in command_line_input, not to the static object itself,
hence why we see a use-after-free.
Fix that by removing the static buffer. I initially changed
command_line_input and other related functions to return an std::string,
which is the obvious but naive solution. The thing is that some callees
don't need to return an allocated string, so this this an unnecessary
pessimization. I changed it to passing in a reference to an std::string
buffer, which the callee can use if it needs to return
dynamically-allocated content. It fills the buffer and returns a
pointers to the C string inside. The callees that don't need to return
dynamically-allocated content simply don't use it.
So, it started with modifying command_line_input as described above, all
the other changes derive directly from that.
One slightly shady thing is in handle_line_of_input, where we now pass a
pointer to an std::string's internal buffer to readline's history_value
function, which takes a `char *`. I'm pretty sure that this function
does not modify the input string, because I was able to change it (with
enough massaging) to take a `const char *`.
A subtle change is that we now clear a UI's line buffer using a
SCOPE_EXIT in command_line_handler, after executing the command.
This was previously done by this line in handle_line_of_input:
/* We have a complete command line now. Prepare for the next
command, but leave ownership of memory to the buffer . */
cmd_line_buffer->used_size = 0;
I think the new way is clearer.
[1] https://inbox.sourceware.org/gdb-patches/becb8438-81ef-8ad8-cc42-fcbfaea8cddd@simark.ca/
[2] https://inbox.sourceware.org/gdb-patches/20221213112241.621889-1-jan.vrany@labware.com/
Change-Id: I8fc89b1c69870c7fc7ad9c1705724bd493596300
Reviewed-By: Tom Tromey <tom@tromey.com>
115 lines
3.2 KiB
C
115 lines
3.2 KiB
C
/* Readline support for Python.
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Copyright (C) 2012-2022 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#include "defs.h"
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#include "python-internal.h"
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#include "top.h"
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#include "cli/cli-utils.h"
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/* Readline function suitable for PyOS_ReadlineFunctionPointer, which
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is used for Python's interactive parser and raw_input. In both
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cases, sys_stdin and sys_stdout are always stdin and stdout
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respectively, as far as I can tell; they are ignored and
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command_line_input is used instead. */
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static char *
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gdbpy_readline_wrapper (FILE *sys_stdin, FILE *sys_stdout,
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#if PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION >= 4
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const char *prompt)
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#else
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char *prompt)
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#endif
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{
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int n;
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const char *p = NULL;
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std::string buffer;
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char *q;
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try
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{
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p = command_line_input (buffer, prompt, "python");
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}
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/* Handle errors by raising Python exceptions. */
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catch (const gdb_exception &except)
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{
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/* Detect user interrupt (Ctrl-C). */
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if (except.reason == RETURN_QUIT)
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return NULL;
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/* The thread state is nulled during gdbpy_readline_wrapper,
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with the original value saved in the following undocumented
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variable (see Python's Parser/myreadline.c and
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Modules/readline.c). */
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PyEval_RestoreThread (_PyOS_ReadlineTState);
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gdbpy_convert_exception (except);
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PyEval_SaveThread ();
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return NULL;
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}
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/* Detect EOF (Ctrl-D). */
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if (p == NULL)
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{
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q = (char *) PyMem_RawMalloc (1);
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if (q != NULL)
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q[0] = '\0';
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return q;
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}
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n = strlen (p);
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/* Copy the line to Python and return. */
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q = (char *) PyMem_RawMalloc (n + 2);
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if (q != NULL)
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{
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strcpy (q, p);
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q[n] = '\n';
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q[n + 1] = '\0';
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}
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return q;
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}
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/* Initialize Python readline support. */
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void
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gdbpy_initialize_gdb_readline (void)
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{
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/* Python's readline module conflicts with GDB's use of readline
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since readline is not reentrant. Ideally, a reentrant wrapper to
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GDB's readline should be implemented to replace Python's readline
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and prevent conflicts. For now, this file implements a
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sys.meta_path finder that simply fails to import the readline
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module. */
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if (PyRun_SimpleString ("\
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import sys\n\
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\n\
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class GdbRemoveReadlineFinder:\n\
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def find_module(self, fullname, path=None):\n\
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if fullname == 'readline' and path is None:\n\
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return self\n\
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return None\n\
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\n\
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def load_module(self, fullname):\n\
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raise ImportError('readline module disabled under GDB')\n\
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\n\
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sys.meta_path.append(GdbRemoveReadlineFinder())\n\
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") == 0)
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PyOS_ReadlineFunctionPointer = gdbpy_readline_wrapper;
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}
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