From: Sergio Durigan Junior <sergiodj@redhat.com>
To: Ruslan Kabatsayev <b7.10110111@gmail.com>
Cc: GDB Patches <gdb-patches@sourceware.org>,
Pedro Alves <palves@redhat.com>, Tom Tromey <tom@tromey.com>,
Eli Zaretskii <eliz@gnu.org>
Subject: Re: [PATCH 5/6] Document Linux-specific possible ptrace restrictions
Date: Wed, 26 Feb 2020 22:08:00 -0000 [thread overview]
Message-ID: <87wo8980ja.fsf@redhat.com> (raw)
In-Reply-To: <CAHEcG94iWZw35ig9U6y1a+9T9WJkoAyU7B4s3UQXnip8Y9iw1w@mail.gmail.com> (Ruslan Kabatsayev's message of "Thu, 27 Feb 2020 00:00:35 +0300")
On Wednesday, February 26 2020, Ruslan Kabatsayev wrote:
> On Wed, 26 Feb 2020 at 23:06, Sergio Durigan Junior <sergiodj@redhat.com> wrote:
>>
>> This patch creates a new "Linux kernel ptrace restrictions" which
>> documents possible causes that can be prevent the inferior from being
>> correctly started/debugged.
>>
>> This has been pre-approved by Eli.
>>
>> gdb/doc/ChangeLog:
>> yyyy-mm-dd Sergio Durigan Junior <sergiodj@redhat.com>
>>
>> * gdb.texinfo (Linux kernel ptrace restrictions): New appendix
>> section.
>> ---
>> gdb/doc/gdb.texinfo | 143 ++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 143 insertions(+)
>>
>> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
>> index f1798e35b5..a95158d5d3 100644
>> --- a/gdb/doc/gdb.texinfo
>> +++ b/gdb/doc/gdb.texinfo
>> @@ -182,6 +182,9 @@ software in general. We will miss him.
>> @value{GDBN}
>> * Operating System Information:: Getting additional information from
>> the operating system
>> +* Linux kernel ptrace restrictions:: Restrictions sometimes
>> + imposed by the Linux
>> + kernel on @code{ptrace}
>> * Trace File Format:: GDB trace file format
>> * Index Section Format:: .gdb_index section format
>> * Man Pages:: Manual pages
>> @@ -45629,6 +45632,146 @@ should contain a comma-separated list of cores that this process
>> is running on. Target may provide additional columns,
>> which @value{GDBN} currently ignores.
>>
>> +@node Linux kernel ptrace restrictions
>> +@appendix Linux kernel @code{ptrace} restrictions
>> +@cindex linux kernel ptrace restrictions, attach
>> +
>> +The @code{ptrace} system call is used by @value{GDBN} and
>> +@code{gdbserver} on GNU/Linux to, among other things, attach to a new
>> +or existing inferior in order to start debugging it. Due to security
>> +concerns, some distributions and vendors disable or severely restrict
>> +the ability to perform these operations, which can make @value{GDBN}
>> +or @code{gdbserver} malfunction. In this section, we will expand on
>> +how this malfunction can manifest itself, and how to modify the
>> +system's settings in order to be able to use @value{GDBN} and
>> +@code{gdbserver} properly.
>> +
>> +@menu
>> +* The error message:: The error message displayed when the
>> + system prevents @value{GDBN}
>> + or @code{gdbserver} from using
>> + @code{ptrace}
>> +* SELinux's deny_ptrace:: SELinux and the @code{deny_ptrace} option
>> +* Yama's ptrace_scope:: Yama and the @code{ptrace_scope} setting
>> +* Docker and seccomp:: Docker and the @code{seccomp}
>> + infrastructure
>> +@end menu
>> +
>> +@node The error message
>> +@appendixsection The error message
>> +
>> +When the system prevents @value{GDBN} or @code{gdbserver} from using
>> +the @code{ptrace} system call, you will likely see a descriptive error
>> +message explaining what is wrong and how to attempt to fix the
>> +problem. For example, when SELinux's @code{deny_ptrace} option is
>> +enabled, you can see:
>> +
>> +@smallexample
>> +$ gdb program
>> +...
>> +(@value{GDBP}) run
>> +Starting program: program
>> +warning: Could not trace the inferior process.
>> +Error:
>> +warning: ptrace: Permission denied
>> +The SELinux 'deny_ptrace' option is enabled and preventing @value{GDBN}
>> +from using 'ptrace'. You can disable it by executing (as root):
>> +
>> + setsebool deny_ptrace off
>> +
>> +If you are debugging the inferior remotely, the instruction(s) above must
>> +be performed in the target system (e.g., where GDBserver is running).
>> +During startup program exited with code 127.
>> +(@value{GDBP})
>> +@end smallexample
>> +
>> +Sometimes, it may not be possible to acquire the necessary data to
>> +determine the root cause of the failure. In this case, you will see a
>> +generic error message pointing you to this section:
>> +
>> +@smallexample
>> +$ gdb program
>> +...
>> +Starting program: program
>> +warning: Could not trace the inferior process.
>> +Error:
>> +warning: ptrace: Permission denied
>> +There might be restrictions preventing ptrace from working. Please see
>> +the appendix "Linux kernel ptrace restrictions" in the GDB documentation
>> +for more details.
>> +During startup program exited with code 127.
>> +(@value{GDBP})
>> +@end smallexample
>> +
>> +@node SELinux's deny_ptrace
>> +@appendixsection SELinux's @code{deny_ptrace}
>> +@cindex SELinux
>> +@cindex deny_ptrace
>> +
>> +If you are using SELinux, you might want to check whether the
>> +@code{deny_ptrace} option is enabled by doing:
>> +
>> +@smallexample
>> +$ getsebool deny_ptrace
>> +deny_ptrace --> on
>> +@end smallexample
>> +
>> +If the option is enabled, you can disable it by doing, as root:
>> +
>> +@smallexample
>> +# setsebool deny_ptrace off
>> +@end smallexample
>> +
>> +The option will be disabled until the next reboot. If you would like
>> +to disable it permanently, you can do (as root):
>> +
>> +@smallexample
>> +# setsebool -P deny_ptrace off
>> +@end smallexample
>> +
>> +@node Yama's ptrace_scope
>> +@appendixsection Yama's @code{ptrace_scope}
>> +@cindex yama, ptrace_scope
>> +
>> +If your system has Yama enabled, you might want to check whether the
>> +@code{ptrace_scope} setting is enabled by checking the value of
>> +@file{/proc/sys/kernel/yama/ptrace_scope}:
>> +
>> +@smallexample
>> +$ cat /proc/sys/kernel/yama/ptrace_scope
>> +0
>> +@end smallexample
>> +
>> +If you see anything other than @code{0}, @value{GDBN} or
>> +@code{gdbserver} can be affected by it. You can temporarily disable
>> +the feature by doing, as root:
>> +
>> +@smallexample
>> +# sysctl kernel.yama.ptrace_scope=0
>> +kernel.yama.ptrace_scope = 0
>> +@end smallexample
>> +
>> +You can make this permanent by doing, as root:
>> +
>> +@smallexample
>> +# sysctl -w kernel.yama.ptrace_scope=0
>> +kernel.yama.ptrace_scope = 0
>> +@end smallexample
>
> Actually, sysctl's "-w" option doesn't make the setting permanent. It
> just lets one write the value. sysctl(8) says about the
> "variable=value" syntax:
> > This requires the -w parameter to use.
> Though I've found that omitting "-w" works exactly the same on
> procps-ng 3.3.9 — checked with strace, which gives identical output in
> both cases.
> In any case, to make this permanent, one has to modify /etc/sysctl.*
> locations (namely, on Ubuntu 14.04 it's /etc/sysctl.d/10-ptrace.conf
> ).
Thanks. I'll remove this part from the docs, then.
--
Sergio
GPG key ID: 237A 54B1 0287 28BF 00EF 31F4 D0EB 7628 65FC 5E36
Please send encrypted e-mail if possible
http://sergiodj.net/
next prev parent reply other threads:[~2020-02-26 22:08 UTC|newest]
Thread overview: 98+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-19 3:29 [PATCH] Improve ptrace-error detection on Linux targets Sergio Durigan Junior
2019-08-19 9:10 ` Ruslan Kabatsayev
2019-08-19 13:47 ` Sergio Durigan Junior
2019-08-19 14:57 ` Ruslan Kabatsayev
2019-08-19 16:30 ` Christian Biesinger via gdb-patches
2019-08-19 17:04 ` Sergio Durigan Junior
2019-08-19 14:33 ` Eli Zaretskii
2019-08-25 22:38 ` Sergio Durigan Junior
2019-08-19 18:26 ` Pedro Alves
2019-08-25 22:40 ` Sergio Durigan Junior
2019-08-26 18:32 ` [PATCH v2] " Sergio Durigan Junior
2019-08-26 18:35 ` Christian Biesinger via gdb-patches
2019-08-26 20:51 ` Sergio Durigan Junior
2019-08-26 18:44 ` Eli Zaretskii
2019-08-29 14:40 ` Pedro Alves
2019-08-29 19:27 ` Sergio Durigan Junior
2019-08-29 19:48 ` Sergio Durigan Junior
2019-08-30 19:03 ` Pedro Alves
2019-08-30 19:51 ` [PATCH] Remove "\nError: " suffix from nat/fork-inferior.c:trace_start_error warning message Sergio Durigan Junior
2019-08-30 19:54 ` Pedro Alves
2019-08-30 21:06 ` Sergio Durigan Junior
2019-08-30 12:45 ` [PATCH v2] Improve ptrace-error detection on Linux targets Pedro Alves
2019-09-04 19:21 ` Sergio Durigan Junior
2019-09-04 19:31 ` Sergio Durigan Junior
2019-09-04 19:58 ` Pedro Alves
2019-09-04 20:21 ` Sergio Durigan Junior
2019-09-04 20:35 ` Pedro Alves
2019-09-04 20:56 ` Sergio Durigan Junior
2019-09-04 21:23 ` Pedro Alves
2019-09-04 21:36 ` Sergio Durigan Junior
2019-09-05 12:19 ` Pedro Alves
2019-09-05 17:58 ` Sergio Durigan Junior
2019-08-30 12:47 ` Pedro Alves
2019-08-30 14:07 ` Eli Zaretskii
2019-08-30 19:44 ` Sergio Durigan Junior
2019-09-04 19:54 ` [PATCH v3] " Sergio Durigan Junior
2019-09-05 17:04 ` Eli Zaretskii
2019-09-11 1:11 ` [PATCH v4] " Sergio Durigan Junior
2019-09-12 12:39 ` Eli Zaretskii
2019-09-12 18:29 ` Sergio Durigan Junior
2019-09-24 20:40 ` Tom Tromey
2019-09-25 14:14 ` Sergio Durigan Junior
2019-09-25 22:04 ` Tom Tromey
2019-09-26 4:22 ` Sergio Durigan Junior
2019-09-26 4:22 ` [PATCH v5] " Sergio Durigan Junior
2019-09-26 17:32 ` Tom Tromey
2019-09-26 17:48 ` Pedro Alves
2019-09-26 17:51 ` Sergio Durigan Junior
2019-09-26 18:14 ` Pedro Alves
2019-09-26 18:25 ` Sergio Durigan Junior
2019-09-26 17:50 ` Sergio Durigan Junior
2019-09-26 18:13 ` Pedro Alves
2019-09-26 18:23 ` Sergio Durigan Junior
2020-02-26 20:06 ` [PATCH 0/6] Improve ptrace-error detection Sergio Durigan Junior
2020-02-26 20:06 ` [PATCH 6/6] Fix comment for 'gdb_dlopen' Sergio Durigan Junior
2020-02-26 20:23 ` Christian Biesinger via gdb-patches
2020-02-26 20:49 ` Sergio Durigan Junior
2020-02-28 15:21 ` Tom Tromey
2020-02-28 16:05 ` Sergio Durigan Junior
2020-02-26 20:06 ` [PATCH 2/6] Don't reset errno/bfd_error on 'throw_perror_with_name' Sergio Durigan Junior
2020-02-28 15:29 ` Tom Tromey
2020-02-28 16:36 ` Sergio Durigan Junior
2020-02-28 18:58 ` Tom Tromey
2020-02-28 19:50 ` Sergio Durigan Junior
2020-02-28 20:06 ` Pedro Alves
2020-02-28 20:35 ` Sergio Durigan Junior
2020-02-28 21:11 ` Pedro Alves
2020-03-02 20:07 ` Sergio Durigan Junior
2020-02-28 19:49 ` Pedro Alves
2020-02-28 20:01 ` Sergio Durigan Junior
2020-02-26 20:06 ` [PATCH 5/6] Document Linux-specific possible ptrace restrictions Sergio Durigan Junior
2020-02-26 21:00 ` Ruslan Kabatsayev
2020-02-26 22:08 ` Sergio Durigan Junior [this message]
2020-02-26 20:06 ` [PATCH 3/6] Expand 'fork_inferior' to check whether 'traceme_fun' succeeded Sergio Durigan Junior
2020-02-26 20:06 ` [PATCH 4/6] Extend GNU/Linux to check for ptrace error Sergio Durigan Junior
2020-02-26 20:06 ` [PATCH 1/6] Introduce scoped_pipe.h Sergio Durigan Junior
2020-02-28 15:23 ` Tom Tromey
2020-02-28 16:08 ` Sergio Durigan Junior
2020-02-28 18:57 ` Tom Tromey
2020-02-28 19:48 ` Sergio Durigan Junior
2020-02-28 19:20 ` Pedro Alves
2020-02-28 19:47 ` Sergio Durigan Junior
2020-02-28 20:07 ` Pedro Alves
[not found] ` <87v9nh3yme.fsf@redhat.com>
2020-03-15 4:21 ` [PATCH 0/6] Improve ptrace-error detection Sergio Durigan Junior
2020-03-15 21:16 ` Kevin Buettner
2020-03-17 15:47 ` [PATCH v2 0/5] " Sergio Durigan Junior
2020-03-17 15:47 ` [PATCH v2 1/5] Introduce scoped_pipe.h Sergio Durigan Junior
2020-03-17 15:47 ` [PATCH v2 2/5] Don't reset errno/bfd_error on 'throw_perror_with_name' Sergio Durigan Junior
2020-03-27 18:20 ` Pedro Alves
2020-03-17 15:47 ` [PATCH v2 3/5] Expand 'fork_inferior' to check whether 'traceme_fun' succeeded Sergio Durigan Junior
2020-03-27 4:14 ` Kevin Buettner
2020-03-27 13:06 ` Pedro Alves
2020-03-17 15:47 ` [PATCH v2 4/5] Extend GNU/Linux to check for ptrace error Sergio Durigan Junior
2020-03-27 15:28 ` Pedro Alves
2020-03-27 17:02 ` Kevin Buettner
2020-03-17 15:47 ` [PATCH v2 5/5] Document Linux-specific possible ptrace restrictions Sergio Durigan Junior
2020-03-20 0:53 ` [PATCH v2 0/5] Improve ptrace-error detection Kevin Buettner
2020-03-24 18:23 ` Sergio Durigan Junior
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