Patch "bio: return EINTR if copying to user space got interrupted" has been added to the 4.4-stable tree

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

bio: return EINTR if copying to user space got interrupted

to the 4.4-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:
bio-return-eintr-if-copying-to-user-space-got-interrupted.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Hannes Reinecke <[email protected]>
Date: Fri, 12 Feb 2016 09:39:15 +0100
Subject: bio: return EINTR if copying to user space got interrupted

From: Hannes Reinecke <[email protected]>

commit 2d99b55d378c996b9692a0c93dd25f4ed5d58934 upstream.

Commit 35dc248383bbab0a7203fca4d722875bc81ef091 introduced a check for current->mm to see if we have a user space context and only copies data if we do. Now if an IO gets interrupted by a signal data isn't copied into user space any more (as we don't have a user space context) but user space isn't notified about it.

This patch modifies the behaviour to return -EINTR from bio_uncopy_user() to notify userland that a signal has interrupted the syscall, otherwise it could lead to a situation where the caller may get a buffer with no data returned.

This can be reproduced by issuing SG_IO ioctl()s in one thread while constantly sending signals to it.

---
 block/bio.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

@@ -1090,9 +1090,12 @@ int bio_uncopy_user(struct bio *bio)
 	if (!bio_flagged(bio, BIO_NULL_MAPPED)) {
 		/*
 		 * if we're in a workqueue, the request is orphaned, so
-		 * don't copy into a random user address space, just free.
+		 * don't copy into a random user address space, just free
+		 * and return -EINTR so user space doesn't expect any data.
 		 */
-		if (current->mm && bio_data_dir(bio) == READ)
+		if (!current->mm)
+			ret = -EINTR;
+		else if (bio_data_dir(bio) == READ)
 			ret = bio_copy_to_iter(bio, bmd->iter);
 		if (bmd->is_our_pages)
 			bio_free_pages(bio);

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

queue-4.4/target-fix-remote-port-tmr-abort-se_cmd-fabric-stop.patch queue-4.4/target-fix-lun_reset-active-tmr-descriptor-handling.patch queue-4.4/target-fix-race-with-scf_send_delayed_tas-handling.patch queue-4.4/bio-return-eintr-if-copying-to-user-space-got-interrupted.patch queue-4.4/target-fix-lun_reset-active-i-o-handling-for-ack_kref.patch queue-4.4/target-fix-tas-handling-for-multi-session-se_node_acls.patch