Patch "md: don't use flush_signals in userspace processes" has been added to the 4.12-stable tree

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

md: don't use flush_signals in userspace processes

to the 4.12-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:
md-don-t-use-flush_signals-in-userspace-processes.patch
and it can be found in the queue-4.12 subdirectory.

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

From: Mikulas Patocka <[email protected]>
Date: Wed, 7 Jun 2017 19:05:31 -0400
Subject: md: don't use flush_signals in userspace processes

From: Mikulas Patocka <[email protected]>

commit f9c79bc05a2a91f4fba8bfd653579e066714b1ec upstream.

The function flush_signals clears all pending signals for the process. It may be used by kernel threads when we need to prepare a kernel thread for responding to signals. However using this function for an userspaces processes is incorrect - clearing signals without the program expecting it can cause misbehavior.

The raid1 and raid5 code uses flush_signals in its request routine because it wants to prepare for an interruptible wait. This patch drops flush_signals and uses sigprocmask instead to block all signals (including SIGKILL) around the schedule() call. The signals are not lost, but the schedule() call won't respond to them.

---
 drivers/md/raid1.c |    5 ++++-
 drivers/md/raid5.c |    5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

@@ -1335,7 +1335,7 @@ static void raid1_write_request(struct m
 		 */
 		DEFINE_WAIT(w);
 		for (;;) {
-			flush_signals(current);
+			sigset_t full, old;
 			prepare_to_wait(&conf->wait_barrier,
 					&w, TASK_INTERRUPTIBLE);
 			if (bio_end_sector(bio) <= mddev->suspend_lo ||

@@ -1345,7 +1345,10 @@ static void raid1_write_request(struct m
 				     bio->bi_iter.bi_sector,
 				     bio_end_sector(bio))))
 				break;
+			sigfillset(&full);
+			sigprocmask(SIG_BLOCK, &full, &old);
 			schedule();
+			sigprocmask(SIG_SETMASK, &old, NULL);
 		}
 		finish_wait(&conf->wait_barrier, &w);
 	}

@@ -5693,12 +5693,15 @@ static void raid5_make_request(struct md
 				 * userspace, we want an interruptible
 				 * wait.
 				 */
-				flush_signals(current);
 				prepare_to_wait(&conf->wait_for_overlap,
 						&w, TASK_INTERRUPTIBLE);
 				if (logical_sector >= mddev->suspend_lo &&
 				    logical_sector < mddev->suspend_hi) {
+					sigset_t full, old;
+					sigfillset(&full);
+					sigprocmask(SIG_BLOCK, &full, &old);
 					schedule();
+					sigprocmask(SIG_SETMASK, &old, NULL);
 					do_prepare = true;
 				}
 				goto retry;

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

queue-4.12/md-don-t-use-flush_signals-in-userspace-processes.patch