From: John Ogness john.ogness@linutronix.de
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.
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 [ zhangyi: 68db0cf10678 does not merged, skip the task_stack.h for 4.4] Signed-off-by: zhangyi (F) yi.zhang@huawei.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/proc/array.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -429,7 +429,15 @@ 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);