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authorRoland Dreier <roland@purestorage.com>2013-08-05 17:55:01 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-09-07 21:58:16 -0700
commitd3ba21877b9488abffd4528aa4b316ec5af27ea3 (patch)
tree3f6705e826e71f1a471a5fdd93d7e460fa16f374
parente51c435e8f955faeb93c8a10f71d7ebf43d887db (diff)
SCSI: sg: Fix user memory corruption when SG_IO is interrupted by a signal
commit 35dc248383bbab0a7203fca4d722875bc81ef091 upstream. There is a nasty bug in the SCSI SG_IO ioctl that in some circumstances leads to one process writing data into the address space of some other random unrelated process if the ioctl is interrupted by a signal. What happens is the following: - A process issues an SG_IO ioctl with direction DXFER_FROM_DEV (ie the underlying SCSI command will transfer data from the SCSI device to the buffer provided in the ioctl) - Before the command finishes, a signal is sent to the process waiting in the ioctl. This will end up waking up the sg_ioctl() code: result = wait_event_interruptible(sfp->read_wait, (srp_done(sfp, srp) || sdp->detached)); but neither srp_done() nor sdp->detached is true, so we end up just setting srp->orphan and returning to userspace: srp->orphan = 1; write_unlock_irq(&sfp->rq_list_lock); return result; /* -ERESTARTSYS because signal hit process */ At this point the original process is done with the ioctl and blithely goes ahead handling the signal, reissuing the ioctl, etc. - Eventually, the SCSI command issued by the first ioctl finishes and ends up in sg_rq_end_io(). At the end of that function, we run through: write_lock_irqsave(&sfp->rq_list_lock, iflags); if (unlikely(srp->orphan)) { if (sfp->keep_orphan) srp->sg_io_owned = 0; else done = 0; } srp->done = done; write_unlock_irqrestore(&sfp->rq_list_lock, iflags); if (likely(done)) { /* Now wake up any sg_read() that is waiting for this * packet. */ wake_up_interruptible(&sfp->read_wait); kill_fasync(&sfp->async_qp, SIGPOLL, POLL_IN); kref_put(&sfp->f_ref, sg_remove_sfp); } else { INIT_WORK(&srp->ew.work, sg_rq_end_io_usercontext); schedule_work(&srp->ew.work); } Since srp->orphan *is* set, we set done to 0 (assuming the userspace app has not set keep_orphan via an SG_SET_KEEP_ORPHAN ioctl), and therefore we end up scheduling sg_rq_end_io_usercontext() to run in a workqueue. - In workqueue context we go through sg_rq_end_io_usercontext() -> sg_finish_rem_req() -> blk_rq_unmap_user() -> ... -> bio_uncopy_user() -> __bio_copy_iov() -> copy_to_user(). The key point here is that we are doing copy_to_user() on a workqueue -- that is, we're on a kernel thread with current->mm equal to whatever random previous user process was scheduled before this kernel thread. So we end up copying whatever data the SCSI command returned to the virtual address of the buffer passed into the original ioctl, but it's quite likely we do this copying into a different address space! As suggested by James Bottomley <James.Bottomley@hansenpartnership.com>, add a check for current->mm (which is NULL if we're on a kernel thread without a real userspace address space) in bio_uncopy_user(), and skip the copy if we're on a kernel thread. There's no reason that I can think of for any caller of bio_uncopy_user() to want to do copying on a kernel thread with a random active userspace address space. Huge thanks to Costa Sapuntzakis <costa@purestorage.com> for the original pointer to this bug in the sg code. Signed-off-by: Roland Dreier <roland@purestorage.com> Tested-by: David Milburn <dmilburn@redhat.com> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: James Bottomley <JBottomley@Parallels.com> [lizf: backported to 3.4: - Use __bio_for_each_segment() instead of bio_for_each_segment_all()] Signed-off-by: Li Zefan <lizefan@huawei.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--fs/bio.c20
1 files changed, 15 insertions, 5 deletions
diff --git a/fs/bio.c b/fs/bio.c
index 84da88539046..c0e5a4e7c514 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -787,12 +787,22 @@ static int __bio_copy_iov(struct bio *bio, struct bio_vec *iovecs,
int bio_uncopy_user(struct bio *bio)
{
struct bio_map_data *bmd = bio->bi_private;
- int ret = 0;
+ struct bio_vec *bvec;
+ int ret = 0, i;
- if (!bio_flagged(bio, BIO_NULL_MAPPED))
- ret = __bio_copy_iov(bio, bmd->iovecs, bmd->sgvecs,
- bmd->nr_sgvecs, bio_data_dir(bio) == READ,
- 0, bmd->is_our_pages);
+ 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.
+ */
+ 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(bvec, bio, i, 0)
+ __free_page(bvec->bv_page);
+ }
bio_free_map_data(bmd);
bio_put(bio);
return ret;