[4.4,5/7] fs/proc: Report eip/esp in /prod/PID/stat for coredumping

Commit Message

Zhang Yi Dec. 2, 2019, 8:35 a.m. UTC

From: John Ogness <[e-mail]>

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 <[e-mail]>
Signed-off-by: John Ogness <[e-mail]>
Reviewed-by: Andy Lutomirski <[e-mail]>
Cc: Tycho Andersen <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Brian Gerst <[e-mail]>
Cc: [e-mail]
Cc: Tetsuo Handa <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Al Viro <[e-mail]>
Cc: Linux API <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Thomas Gleixner <[e-mail]>

[ zhangyi: 68db0cf10678 does not merged, skip the task_stack.h for 4.4]

Signed-off-by: zhangyi (F) <[e-mail]>
---
 fs/proc/array.c | 8 ++++++++
 1 file changed, 8 insertions(+)

Patch

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 618c83f1866d..c3e1732bcaa5 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -429,7 +429,15 @@  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);