From 11646ff9e6874d205ab92af605db6b90fbe214d1 Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@redhat.com>
Date: Tue, 9 Sep 2014 19:12:32 +0100
Subject: [PATCH] KEYS: Fix termination condition in assoc array garbage
 collection

It is possible for an associative array to end up with a shortcut node at the
root of the tree, if there are more than fan-out nodes in the tree, but they
all crowd into the same slot in the lowest level (ie. they all have the same
first nibble of their index keys).

When assoc_array_gc() returns back up the tree after scanning some leaves, it
can fall off of the root and crash because it assumes that the back pointer
from a shortcut (after label ascend_old_tree) must point to a normal node -
which isn't true of a shortcut node at the root.

Should we find we're ascending rootwards over a shortcut, we should check to
see if the backpointer is zero - and if it is, we have completed the scan.

This particular bug cannot occur if the root node is not a shortcut - ie. if
you have fewer than 17 keys in a keyring or if you have at least two keys that
sit into separate slots (eg. a keyring and a non keyring).

If we do fall off of the top of the tree, we get the following oops:

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
  IP: [<ffffffff8136cea7>] assoc_array_gc+0x2f7/0x540
  PGD dae15067 PUD cfc24067 PMD 0
  Oops: 0000 [#1] SMP
  Modules linked in: xt_nat xt_mark nf_conntrack_netbios_ns nf_conntrack_broadcast ip6t_rpfilter ip6t_REJECT xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_ni
  CPU: 0 PID: 26011 Comm: kworker/0:1 Not tainted 3.14.9-200.fc20.x86_64 #1
  Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
  Workqueue: events key_garbage_collector
  task: ffff8800918bd580 ti: ffff8800aac14000 task.ti: ffff8800aac14000
  RIP: 0010:[<ffffffff8136cea7>] [<ffffffff8136cea7>] assoc_array_gc+0x2f7/0x540
  RSP: 0018:ffff8800aac15d40  EFLAGS: 00010206
  RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff8800aaecacc0
  RDX: ffff8800daecf440 RSI: 0000000000000001 RDI: ffff8800aadc2bc0
  RBP: ffff8800aac15da8 R08: 0000000000000001 R09: 0000000000000003
  R10: ffffffff8136ccc7 R11: 0000000000000000 R12: 0000000000000000
  R13: 0000000000000000 R14: 0000000000000070 R15: 0000000000000001
  FS:  0000000000000000(0000) GS:ffff88011fc00000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
  CR2: 0000000000000018 CR3: 00000000db10d000 CR4: 00000000000006f0
  Stack:
   ffff8800aac15d50 0000000000000011 ffff8800aac15db8 ffffffff812e2a70
   ffff880091a00600 0000000000000000 ffff8800aadc2bc3 00000000cd42c987
   ffff88003702df20 ffff88003702dfa0 0000000053b65c09 ffff8800aac15fd8
  Call Trace:
   [<ffffffff812e2a70>] ? keyring_detect_cycle_iterator+0x30/0x30
   [<ffffffff812e3e75>] keyring_gc+0x75/0x80
   [<ffffffff812e1424>] key_garbage_collector+0x154/0x3c0
   [<ffffffff810a67b6>] process_one_work+0x176/0x430
   [<ffffffff810a744b>] worker_thread+0x11b/0x3a0
   [<ffffffff810a7330>] ? rescuer_thread+0x3b0/0x3b0
   [<ffffffff810ae1a8>] kthread+0xd8/0xf0
   [<ffffffff810ae0d0>] ? insert_kthread_work+0x40/0x40
   [<ffffffff816ffb7c>] ret_from_fork+0x7c/0xb0
   [<ffffffff810ae0d0>] ? insert_kthread_work+0x40/0x40
  Code: 08 4c 8b 22 0f 84 bf 00 00 00 41 83 c7 01 49 83 e4 fc 41 83 ff 0f 4c 89 65 c0 0f 8f 5a fe ff ff 48 8b 45 c0 4d 63 cf 49 83 c1 02 <4e> 8b 34 c8 4d 85 f6 0f 84 be 00 00 00 41 f6 c6 01 0f 84 92
  RIP  [<ffffffff8136cea7>] assoc_array_gc+0x2f7/0x540
   RSP <ffff8800aac15d40>
  CR2: 0000000000000018
  ---[ end trace 1129028a088c0cbd ]---

Bugzilla: 1116347
Upstream-status: ??

Signed-off-by: David Howells <dhowells@redhat.com>
---
 lib/assoc_array.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/assoc_array.c b/lib/assoc_array.c
index ae146f0734eb..2404d03e251a 100644
--- a/lib/assoc_array.c
+++ b/lib/assoc_array.c
@@ -1723,11 +1723,13 @@ ascend_old_tree:
 		shortcut = assoc_array_ptr_to_shortcut(ptr);
 		slot = shortcut->parent_slot;
 		cursor = shortcut->back_pointer;
+		if (!cursor)
+			goto gc_complete;
 	} else {
 		slot = node->parent_slot;
 		cursor = ptr;
 	}
-	BUG_ON(!ptr);
+	BUG_ON(!cursor);
 	node = assoc_array_ptr_to_node(cursor);
 	slot++;
 	goto continue_node;
-- 
1.9.3