Commit 7a4deea1 authored by Matthew Wilcox's avatar Matthew Wilcox Committed by Linus Torvalds
Browse files

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

Fixes: 0a835c4f

 ("Reimplement IDR and IDA using the radix tree")
Reported-by: default avatar <>
Debugged-by: default avatarRoman Kagan <>
Signed-off-by: default avatarMatthew Wilcox <>
Cc: <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 3373de20
......@@ -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;
......@@ -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);
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);
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