[PATCH 3.16.y-ckt 013/142] bio: return EINTR if copying to user space got interrupted

[Luis Henriques]

3.16.7-ckt26 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Hannes Reinecke <hare@xxxxxxx>

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.

Fixes: 35dc248 [SCSI] sg: Fix user memory corruption when SG_IO is interrupted by a signal
Signed-off-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxx>
[ luis: backported to 3.16: based on Johannes' backport to 3.14 ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 block/bio.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 6467e6afdcd9..529e4195724e 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1110,9 +1110,12 @@ int bio_uncopy_user(struct bio *bio)
 			ret = __bio_copy_iov(bio, bmd->sgvecs, bmd->nr_sgvecs,
 					     bio_data_dir(bio) == READ,
 					     0, bmd->is_our_pages);
-		else if (bmd->is_our_pages)
-			bio_for_each_segment_all(bvec, bio, i)
-				__free_page(bvec->bv_page);
+		else {
+			ret = -EINTR;
+			if (bmd->is_our_pages)
+				bio_for_each_segment_all(bvec, bio, i)
+					__free_page(bvec->bv_page);
+		}
 	}
 	kfree(bmd);
 	bio_put(bio);