2014-09-12 17:26:54 +00:00
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From 02c3c0f0c83483a79783b211ef1bbd79ef0bd360 Mon Sep 17 00:00:00 2001
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2014-09-10 13:55:35 +00:00
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From: David Howells <dhowells@redhat.com>
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Date: Tue, 9 Sep 2014 19:12:32 +0100
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Subject: [PATCH] KEYS: Fix termination condition in assoc array garbage
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collection
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It is possible for an associative array to end up with a shortcut node at the
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root of the tree, if there are more than fan-out nodes in the tree, but they
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all crowd into the same slot in the lowest level (ie. they all have the same
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first nibble of their index keys).
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When assoc_array_gc() returns back up the tree after scanning some leaves, it
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can fall off of the root and crash because it assumes that the back pointer
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from a shortcut (after label ascend_old_tree) must point to a normal node -
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which isn't true of a shortcut node at the root.
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Should we find we're ascending rootwards over a shortcut, we should check to
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see if the backpointer is zero - and if it is, we have completed the scan.
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This particular bug cannot occur if the root node is not a shortcut - ie. if
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you have fewer than 17 keys in a keyring or if you have at least two keys that
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sit into separate slots (eg. a keyring and a non keyring).
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If we do fall off of the top of the tree, we get the following oops:
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BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
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IP: [<ffffffff8136cea7>] assoc_array_gc+0x2f7/0x540
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PGD dae15067 PUD cfc24067 PMD 0
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Oops: 0000 [#1] SMP
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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
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CPU: 0 PID: 26011 Comm: kworker/0:1 Not tainted 3.14.9-200.fc20.x86_64 #1
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Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
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Workqueue: events key_garbage_collector
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task: ffff8800918bd580 ti: ffff8800aac14000 task.ti: ffff8800aac14000
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RIP: 0010:[<ffffffff8136cea7>] [<ffffffff8136cea7>] assoc_array_gc+0x2f7/0x540
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RSP: 0018:ffff8800aac15d40 EFLAGS: 00010206
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RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff8800aaecacc0
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RDX: ffff8800daecf440 RSI: 0000000000000001 RDI: ffff8800aadc2bc0
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RBP: ffff8800aac15da8 R08: 0000000000000001 R09: 0000000000000003
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R10: ffffffff8136ccc7 R11: 0000000000000000 R12: 0000000000000000
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R13: 0000000000000000 R14: 0000000000000070 R15: 0000000000000001
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FS: 0000000000000000(0000) GS:ffff88011fc00000(0000) knlGS:0000000000000000
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CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
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CR2: 0000000000000018 CR3: 00000000db10d000 CR4: 00000000000006f0
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Stack:
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ffff8800aac15d50 0000000000000011 ffff8800aac15db8 ffffffff812e2a70
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ffff880091a00600 0000000000000000 ffff8800aadc2bc3 00000000cd42c987
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ffff88003702df20 ffff88003702dfa0 0000000053b65c09 ffff8800aac15fd8
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Call Trace:
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[<ffffffff812e2a70>] ? keyring_detect_cycle_iterator+0x30/0x30
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[<ffffffff812e3e75>] keyring_gc+0x75/0x80
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[<ffffffff812e1424>] key_garbage_collector+0x154/0x3c0
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[<ffffffff810a67b6>] process_one_work+0x176/0x430
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[<ffffffff810a744b>] worker_thread+0x11b/0x3a0
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[<ffffffff810a7330>] ? rescuer_thread+0x3b0/0x3b0
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[<ffffffff810ae1a8>] kthread+0xd8/0xf0
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[<ffffffff810ae0d0>] ? insert_kthread_work+0x40/0x40
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[<ffffffff816ffb7c>] ret_from_fork+0x7c/0xb0
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[<ffffffff810ae0d0>] ? insert_kthread_work+0x40/0x40
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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
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RIP [<ffffffff8136cea7>] assoc_array_gc+0x2f7/0x540
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RSP <ffff8800aac15d40>
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CR2: 0000000000000018
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---[ end trace 1129028a088c0cbd ]---
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Bugzilla: 1116347
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Upstream-status: ??
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Signed-off-by: David Howells <dhowells@redhat.com>
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---
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lib/assoc_array.c | 4 +++-
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1 file changed, 3 insertions(+), 1 deletion(-)
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diff --git a/lib/assoc_array.c b/lib/assoc_array.c
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index ae146f0734eb..2404d03e251a 100644
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--- a/lib/assoc_array.c
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+++ b/lib/assoc_array.c
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@@ -1723,11 +1723,13 @@ ascend_old_tree:
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shortcut = assoc_array_ptr_to_shortcut(ptr);
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slot = shortcut->parent_slot;
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cursor = shortcut->back_pointer;
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+ if (!cursor)
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+ goto gc_complete;
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} else {
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slot = node->parent_slot;
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cursor = ptr;
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}
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- BUG_ON(!ptr);
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+ BUG_ON(!cursor);
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node = assoc_array_ptr_to_node(cursor);
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slot++;
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goto continue_node;
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--
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1.9.3
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