From 7a4deea1aa8bddfed4ef1b35fc2b6732563d8ad5 Mon Sep 17 00:00:00 2001
From: Matthew Wilcox <mawilcox@microsoft.com>
Date: Fri, 25 May 2018 14:47:24 -0700
Subject: [PATCH] idr: fix invalid ptr dereference on item delete
Git-commit: 7a4deea1aa8bddfed4ef1b35fc2b6732563d8ad5
Patch-mainline: v4.17-rc7
References: bsc#1051510

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

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

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 43e0cbedc3a0..a9e41aed6de4 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -2034,10 +2034,12 @@ void *radix_tree_delete_item(struct radix_tree_root *root,
 			     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 --git a/tools/testing/radix-tree/idr-test.c b/tools/testing/radix-tree/idr-test.c
index 6c645eb77d42..ee820fcc29b0 100644
--- a/tools/testing/radix-tree/idr-test.c
+++ b/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);
-- 
2.18.0