bio: return EINTR if copying to user space got interrupted

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@suse.de>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
[bwh: Backported to 3.2:
 - Adjust filename
 - Put the assignment in the existing 'else' block]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/bio.c b/fs/bio.c
index b84d851..55b5188 100644 (file)
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -793,15 +793,19 @@ 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
        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)
                        ret = __bio_copy_iov(bio, bmd->iovecs, bmd->sgvecs,
                                             bmd->nr_sgvecs, bio_data_dir(bio) == READ,
                                             0, bmd->is_our_pages);
                 */
                if (current->mm)
                        ret = __bio_copy_iov(bio, bmd->iovecs, 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);
+               }

        }
        bio_free_map_data(bmd);
        bio_put(bio);
        }
        bio_free_map_data(bmd);
        bio_put(bio);