Patch "fs/proc: Report eip/esp in /prod/PID/stat for coredumping" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
fs-proc-report-eip-esp-in-prod-pid-stat-for-coredumping.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: John Ogness <[email protected]>
Date: Thu, 14 Sep 2017 11:42:17 +0200
Subject: fs/proc: Report eip/esp in /prod/PID/stat for coredumping

From: John Ogness <[email protected]>

commit fd7d56270b526ca3ed0c224362e3c64a0f86687a upstream.

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.

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

@@ -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
 		 * 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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/fs-proc-report-eip-esp-in-prod-pid-stat-for-coredumping.patch