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[PATCH] fs/proc: report eip/esp in /prod/PID/stat for coredumping

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  [PATCH] fs/proc: report eip/esp in /prod/PID/stat for coredumping John Ogness <john.ogness@linutronix.de> - 2017-09-14 11:50 +0200
    Re: [PATCH] fs/proc: report eip/esp in /prod/PID/stat for coredumping Andy Lutomirski <luto@kernel.org> - 2017-09-14 17:00 +0200
    Re: [PATCH] fs/proc: report eip/esp in /prod/PID/stat for  coredumping Thomas Gleixner <tglx@linutronix.de> - 2017-09-14 17:40 +0200
      Re: [PATCH] fs/proc: report eip/esp in /prod/PID/stat for coredumping Linus Torvalds <torvalds@linux-foundation.org> - 2017-09-15 21:10 +0200
        Re: [PATCH] fs/proc: report eip/esp in /prod/PID/stat for coredumping Ingo Molnar <mingo@kernel.org> - 2017-09-15 23:10 +0200
    [tip:core/urgent] fs/proc: Report eip/esp in /prod/PID/stat for  coredumping tip-bot for John Ogness <tipbot@zytor.com> - 2017-09-15 23:20 +0200
    [tip:core/urgent] fs/proc: Report eip/esp in /prod/PID/stat for  coredumping tip-bot for John Ogness <tipbot@zytor.com> - 2017-09-15 23:50 +0200

#1732144 — [PATCH] fs/proc: report eip/esp in /prod/PID/stat for coredumping

Commit 0a1eb2d474ed ("fs/proc: Stop reporting eip and esp in
/proc/PID/stat") stopped reporting eip/esp because it is
racey and dangerous for executing tasks. The comment adds:

    As far as I know, there are no use programs that make any
    material use of these fields, so just get rid of them.

However, existing userspace core-dump-handler applications (for
example, minicoredumper) are using these fields since they
provide an excellent cross-platform interface to these valuable
pointers. So that commit introduced a user space visible
regression.

Partially revert the change and make the readout possible for
tasks with the proper permissions and only if the target task
has the PF_DUMPCORE flag set.

Reported-by: Marco Felsch <marco.felsch@preh.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Cc: stable@vger.kernel.org
Fixes: 0a1eb2d474ed ("fs/proc: Stop reporting eip and esp in> /proc/PID/stat")
---
 fs/proc/array.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 88c3555..696cc68 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -421,7 +421,15 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 		 * esp and eip are intentionally zeroed out.  There is no
 		 * non-racy way to read them without freezing the task.
 		 * Programs that need reliable values can use ptrace(2).
+		 *
+		 * The only exception is if the task is core dumping because
+		 * a program is not able to use ptrace(2) in that case. It is
+		 * safe because the task has stopped executing permanently.
 		 */
+		if (permitted && (task->flags & PF_DUMPCORE)) {
+			eip = KSTK_EIP(task);
+			esp = KSTK_ESP(task);
+		}
 	}
 
 	get_task_comm(tcomm, task);
-- 
1.7.10.4

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#1732339

On Thu, Sep 14, 2017 at 2:42 AM, John Ogness <john.ogness@linutronix.de> wrote:
> Commit 0a1eb2d474ed ("fs/proc: Stop reporting eip and esp in
> /proc/PID/stat") stopped reporting eip/esp because it is
> racey and dangerous for executing tasks. The comment adds:
>
>     As far as I know, there are no use programs that make any
>     material use of these fields, so just get rid of them.
>
> However, existing userspace core-dump-handler applications (for
> example, minicoredumper) are using these fields since they
> provide an excellent cross-platform interface to these valuable
> pointers. So that commit introduced a user space visible
> regression.
>
> Partially revert the change and make the readout possible for
> tasks with the proper permissions and only if the target task
> has the PF_DUMPCORE flag set.

Looks okay to me.

Reviewed-by: Andy Lutomirski <luto@kernel.org>

--Andy

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#1732358 — Re: [PATCH] fs/proc: report eip/esp in /prod/PID/stat for coredumping

On Thu, 14 Sep 2017, John Ogness wrote:

> Commit 0a1eb2d474ed ("fs/proc: Stop reporting eip and esp in
> /proc/PID/stat") stopped reporting eip/esp because it is
> racey and dangerous for executing tasks. The comment adds:
> 
>     As far as I know, there are no use programs that make any
>     material use of these fields, so just get rid of them.
> 
> However, existing userspace core-dump-handler applications (for
> example, minicoredumper) are using these fields since they
> provide an excellent cross-platform interface to these valuable
> pointers. So that commit introduced a user space visible
> regression.
> 
> Partially revert the change and make the readout possible for
> tasks with the proper permissions and only if the target task
> has the PF_DUMPCORE flag set.

Duh, I completely forgot about mini core dumper when I acked that commit.

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

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#1733032

Ingo, I'm assuming I'll get this from the -tip tree, which is where I
got the original commit that this fixes.

Thanks,
                   Linus

On Thu, Sep 14, 2017 at 8:37 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Thu, 14 Sep 2017, John Ogness wrote:
>
>> Commit 0a1eb2d474ed ("fs/proc: Stop reporting eip and esp in
>> /proc/PID/stat") stopped reporting eip/esp because it is
>> racey and dangerous for executing tasks. The comment adds:
...
>> Partially revert the change and make the readout possible for
>> tasks with the proper permissions and only if the target task
>> has the PF_DUMPCORE flag set.
>
> Duh, I completely forgot about mini core dumper when I acked that commit.
>
> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

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#1733092

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> Ingo, I'm assuming I'll get this from the -tip tree, which is where I
> got the original commit that this fixes.
> 
> Thanks,
>                    Linus

Yeah, will do!

Thanks,

	Ingo

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#1733099 — [tip:core/urgent] fs/proc: Report eip/esp in /prod/PID/stat for coredumping

Commit-ID:  451eb3f2053ea4eeb40f94947c542cfbd7636186
Gitweb:     http://git.kernel.org/tip/451eb3f2053ea4eeb40f94947c542cfbd7636186
Author:     John Ogness <john.ogness@linutronix.de>
AuthorDate: Thu, 14 Sep 2017 11:42:17 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 15 Sep 2017 23:04:59 +0200

fs/proc: Report eip/esp in /prod/PID/stat for coredumping

Commit 0a1eb2d474ed ("fs/proc: Stop reporting eip and esp in
/proc/PID/stat") stopped reporting eip/esp because it is
racey and dangerous for executing tasks. The comment adds:

    As far as I know, there are no use programs that make any
    material use of these fields, so just get rid of them.

However, existing userspace core-dump-handler applications (for
example, minicoredumper) are using these fields since they
provide an excellent cross-platform interface to these valuable
pointers. So that commit introduced a user space visible
regression.

Partially revert the change and make the readout possible for
tasks with the proper permissions and only if the target task
has the PF_DUMPCORE flag set.

Fixes: 0a1eb2d474ed ("fs/proc: Stop reporting eip and esp in> /proc/PID/stat")
Reported-by: Marco Felsch <marco.felsch@preh.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Cc: Tycho Andersen <tycho.andersen@canonical.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: stable@vger.kernel.org
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linux API <linux-api@vger.kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/87poatfwg6.fsf@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 fs/proc/array.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 88c3555..696cc68 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -421,7 +421,15 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 		 * esp and eip are intentionally zeroed out.  There is no
 		 * non-racy way to read them without freezing the task.
 		 * Programs that need reliable values can use ptrace(2).
+		 *
+		 * The only exception is if the task is core dumping because
+		 * a program is not able to use ptrace(2) in that case. It is
+		 * safe because the task has stopped executing permanently.
 		 */
+		if (permitted && (task->flags & PF_DUMPCORE)) {
+			eip = KSTK_EIP(task);
+			esp = KSTK_ESP(task);
+		}
 	}
 
 	get_task_comm(tcomm, task);

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#1733107 — [tip:core/urgent] fs/proc: Report eip/esp in /prod/PID/stat for coredumping

Commit-ID:  fd7d56270b526ca3ed0c224362e3c64a0f86687a
Gitweb:     http://git.kernel.org/tip/fd7d56270b526ca3ed0c224362e3c64a0f86687a
Author:     John Ogness <john.ogness@linutronix.de>
AuthorDate: Thu, 14 Sep 2017 11:42:17 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 15 Sep 2017 23:31:16 +0200

fs/proc: Report eip/esp in /prod/PID/stat for coredumping

Commit 0a1eb2d474ed ("fs/proc: Stop reporting eip and esp in
/proc/PID/stat") stopped reporting eip/esp because it is
racy and dangerous for executing tasks. The comment adds:

    As far as I know, there are no use programs that make any
    material use of these fields, so just get rid of them.

However, existing userspace core-dump-handler applications (for
example, minicoredumper) are using these fields since they
provide an excellent cross-platform interface to these valuable
pointers. So that commit introduced a user space visible
regression.

Partially revert the change and make the readout possible for
tasks with the proper permissions and only if the target task
has the PF_DUMPCORE flag set.

Fixes: 0a1eb2d474ed ("fs/proc: Stop reporting eip and esp in> /proc/PID/stat")
Reported-by: Marco Felsch <marco.felsch@preh.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Cc: Tycho Andersen <tycho.andersen@canonical.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: stable@vger.kernel.org
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linux API <linux-api@vger.kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/87poatfwg6.fsf@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 fs/proc/array.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 88c3555..525157c 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -62,6 +62,7 @@
 #include <linux/mman.h>
 #include <linux/sched/mm.h>
 #include <linux/sched/numa_balancing.h>
+#include <linux/sched/task_stack.h>
 #include <linux/sched/task.h>
 #include <linux/sched/cputime.h>
 #include <linux/proc_fs.h>
@@ -421,7 +422,15 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 		 * esp and eip are intentionally zeroed out.  There is no
 		 * non-racy way to read them without freezing the task.
 		 * Programs that need reliable values can use ptrace(2).
+		 *
+		 * The only exception is if the task is core dumping because
+		 * a program is not able to use ptrace(2) in that case. It is
+		 * safe because the task has stopped executing permanently.
 		 */
+		if (permitted && (task->flags & PF_DUMPCORE)) {
+			eip = KSTK_EIP(task);
+			esp = KSTK_ESP(task);
+		}
 	}
 
 	get_task_comm(tcomm, task);

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