[patch 03/16] idr: fix invalid ptr dereference on item delete

[akpm@linux-foundation.org]

From: Matthew Wilcox <mawilcox@microsoft.com>
Subject: idr: fix invalid ptr dereference on item delete

If the radix tree underlying the IDR happens to be full and we attempt to
remove an id which is larger than any id in the IDR, we will call
__radix_tree_delete() with an uninitialised 'slot' pointer, at which point
anything could happen.  This was easiest to hit with a single entry at id
0 and attempting to remove a non-0 id, but it could have happened with 64
entries and attempting to remove an id >= 64.

Roman said:

  The syzcaller test boils down to opening /dev/kvm, creating an
  eventfd, and calling a couple of KVM ioctls.  None of this requires
  superuser.  And the result is dereferencing an uninitialized pointer
  which is likely a crash.  The specific path caught by syzbot is via
  KVM_HYPERV_EVENTD ioctl which is new in 4.17.  But I guess there are
  other user-triggerable paths, so cc:stable is probably justified.

Matthew added:

  We have around 250 calls to idr_remove() in the kernel today.  Many
  of them pass an ID which is embedded in the object they're removing,
  so they're safe.  Picking a few likely candidates:

  drivers/firewire/core-cdev.c looks unsafe; the ID comes from an ioctl.
  drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c is similar
  drivers/atm/nicstar.c could be taken down by a handcrafted packet

Link: http://lkml.kernel.org/r/20180518175025.GD6361@bombadil.infradead.org
Fixes: 0a835c4f090a ("Reimplement IDR and IDA using the radix tree")
Reported-by: <syzbot+35666cba7f0a337e2e79@syzkaller.appspotmail.com>
Debugged-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/radix-tree.c                    |    4 +++-
 tools/testing/radix-tree/idr-test.c |    7 +++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff -puN lib/radix-tree.c~idr-fix-invalid-ptr-dereference-on-item-delete lib/radix-tree.c
--- a/lib/radix-tree.c~idr-fix-invalid-ptr-dereference-on-item-delete
+++ a/lib/radix-tree.c
@@ -2034,10 +2034,12 @@ void *radix_tree_delete_item(struct radi
 			     unsigned long index, void *item)
 {
 	struct radix_tree_node *node = NULL;
-	void __rcu **slot;
+	void __rcu **slot = NULL;
 	void *entry;
 
 	entry = __radix_tree_lookup(root, index, &node, &slot);
+	if (!slot)
+		return NULL;
 	if (!entry && (!is_idr(root) || node_tag_get(root, node, IDR_FREE,
 						get_slot_offset(node, slot))))
 		return NULL;
diff -puN tools/testing/radix-tree/idr-test.c~idr-fix-invalid-ptr-dereference-on-item-delete tools/testing/radix-tree/idr-test.c
--- a/tools/testing/radix-tree/idr-test.c~idr-fix-invalid-ptr-dereference-on-item-delete
+++ a/tools/testing/radix-tree/idr-test.c
@@ -252,6 +252,13 @@ void idr_checks(void)
 	idr_remove(&idr, 3);
 	idr_remove(&idr, 0);
 
+	assert(idr_alloc(&idr, DUMMY_PTR, 0, 0, GFP_KERNEL) == 0);
+	idr_remove(&idr, 1);
+	for (i = 1; i < RADIX_TREE_MAP_SIZE; i++)
+		assert(idr_alloc(&idr, DUMMY_PTR, 0, 0, GFP_KERNEL) == i);
+	idr_remove(&idr, 1 << 30);
+	idr_destroy(&idr);
+
 	for (i = INT_MAX - 3UL; i < INT_MAX + 1UL; i++) {
 		struct item *item = item_create(i, 0);
 		assert(idr_alloc(&idr, item, i, i + 10, GFP_KERNEL) == i);
_