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Subject[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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