bio: return EINTR if copying to user space got interrupted

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@suse.de>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Cc: stable@vger.kernel.org # v.3.11+
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/block/bio.c b/block/bio.c
index f53a691b6533..cf7591551b17 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -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);