IB/hfi1: Ensure correct mm is used at all times

Two earlier bug fixes have created a security problem in the hfi1
driver. One fix aimed to solve an issue where current->mm was not valid
when closing the hfi1 cdev. It attempted to do this by saving a cached
value of the current->mm pointer at file open time. This is a problem if
another process with access to the FD calls in via write() or ioctl() to
pin pages via the hfi driver. The other fix tried to solve a use after
free by taking a reference on the mm.

To fix this correctly we use the existing cached value of the mm in the
mmu notifier. Now we can check in the insert, evict, etc. routines that
current->mm matched what the notifier was registered for. If not, then
don't allow access. The register of the mmu notifier will save the mm
pointer.

Since in do_exit() the exit_mm() is called before exit_files(), which
would call our close routine a reference is needed on the mm. We rely on
the mmgrab done by the registration of the notifier, whereas before it was
explicit. The mmu notifier deregistration happens when the user context is
torn down, the creation of which triggered the registration.

Also of note is we do not do any explicit work to protect the interval
tree notifier. It doesn't seem that this is going to be needed since we
aren't actually doing anything with current->mm. The interval tree
notifier stuff still has a FIXME noted from a previous commit that will be
addressed in a follow on patch.

Cc: <stable@vger.kernel.org>
Fixes: e0cf75deab81 ("IB/hfi1: Fix mm_struct use after free")
Fixes: 3faa3d9a308e ("IB/hfi1: Make use of mm consistent")
Link: https://lore.kernel.org/r/20201125210112.104301.51331.stgit@awfm-01.aw.intel.com
Suggested-by: Jann Horn <jannh@google.com>
Reported-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@cornelisnetworks.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/drivers/infiniband/hw/hfi1/user_sdma.h b/drivers/infiniband/hw/hfi1/user_sdma.h
index 9972e0e6545e..1e8c02fe8ad1 100644
--- a/drivers/infiniband/hw/hfi1/user_sdma.h
+++ b/drivers/infiniband/hw/hfi1/user_sdma.h
@@ -1,6 +1,7 @@
 #ifndef _HFI1_USER_SDMA_H
 #define _HFI1_USER_SDMA_H
 /*
+ * Copyright(c) 2020 - Cornelis Networks, Inc.
  * Copyright(c) 2015 - 2018 Intel Corporation.
  *
  * This file is provided under a dual BSD/GPLv2 license.  When using or
@@ -133,7 +134,6 @@ struct hfi1_user_sdma_pkt_q {
 	unsigned long unpinned;
 	struct mmu_rb_handler *handler;
 	atomic_t n_locked;
-	struct mm_struct *mm;
 };
 
 struct hfi1_user_sdma_comp_q {
@@ -250,4 +250,9 @@ int hfi1_user_sdma_process_request(struct hfi1_filedata *fd,
 				   struct iovec *iovec, unsigned long dim,
 				   unsigned long *count);
 
+static inline struct mm_struct *mm_from_sdma_node(struct sdma_mmu_node *node)
+{
+	return node->rb.handler->mn.mm;
+}
+
 #endif /* _HFI1_USER_SDMA_H */