From: Florian Westphal fw@strlen.de
commit fd709721352dd5239056eacaded00f2244e6ef58 upstream.
syzbot reported following spat:
BUG: KASAN: use-after-free in __write_once_size include/linux/compiler.h:221 BUG: KASAN: use-after-free in hlist_del_rcu include/linux/rculist.h:455 BUG: KASAN: use-after-free in xfrm_hash_rebuild+0xa0d/0x1000 net/xfrm/xfrm_policy.c:1318 Write of size 8 at addr ffff888095e79c00 by task kworker/1:3/8066 Workqueue: events xfrm_hash_rebuild Call Trace: __write_once_size include/linux/compiler.h:221 [inline] hlist_del_rcu include/linux/rculist.h:455 [inline] xfrm_hash_rebuild+0xa0d/0x1000 net/xfrm/xfrm_policy.c:1318 process_one_work+0x814/0x1130 kernel/workqueue.c:2269 Allocated by task 8064: __kmalloc+0x23c/0x310 mm/slab.c:3669 kzalloc include/linux/slab.h:742 [inline] xfrm_hash_alloc+0x38/0xe0 net/xfrm/xfrm_hash.c:21 xfrm_policy_init net/xfrm/xfrm_policy.c:4036 [inline] xfrm_net_init+0x269/0xd60 net/xfrm/xfrm_policy.c:4120 ops_init+0x336/0x420 net/core/net_namespace.c:130 setup_net+0x212/0x690 net/core/net_namespace.c:316
The faulting address is the address of the old chain head, free'd by xfrm_hash_resize().
In xfrm_hash_rehash(), chain heads get re-initialized without any hlist_del_rcu:
for (i = hmask; i >= 0; i--) INIT_HLIST_HEAD(odst + i);
Then, hlist_del_rcu() gets called on the about to-be-reinserted policy when iterating the per-net list of policies.
hlist_del_rcu() will then make chain->first be nonzero again:
static inline void __hlist_del(struct hlist_node *n) { struct hlist_node *next = n->next; // address of next element in list struct hlist_node **pprev = n->pprev;// location of previous elem, this // can point at chain->first WRITE_ONCE(*pprev, next); // chain->first points to next elem if (next) next->pprev = pprev;
Then, when we walk chainlist to find insertion point, we may find a non-empty list even though we're supposedly reinserting the first policy to an empty chain.
To fix this first unlink all exact and inexact policies instead of zeroing the list heads.
Add the commands equivalent to the syzbot reproducer to xfrm_policy.sh, without fix KASAN catches the corruption as it happens, SLUB poisoning detects it a bit later.
Reported-by: syzbot+0165480d4ef07360eeda@syzkaller.appspotmail.com Fixes: 1548bc4e0512 ("xfrm: policy: delete inexact policies from inexact list on hash rebuild") Signed-off-by: Florian Westphal fw@strlen.de Signed-off-by: Steffen Klassert steffen.klassert@secunet.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- net/xfrm/xfrm_policy.c | 12 +++++++----- tools/testing/selftests/net/xfrm_policy.sh | 27 ++++++++++++++++++++++++++- 2 files changed, 33 insertions(+), 6 deletions(-)
--- a/net/xfrm/xfrm_policy.c +++ b/net/xfrm/xfrm_policy.c @@ -1280,13 +1280,17 @@ static void xfrm_hash_rebuild(struct wor
hlist_for_each_entry_safe(policy, n, &net->xfrm.policy_inexact[dir], - bydst_inexact_list) + bydst_inexact_list) { + hlist_del_rcu(&policy->bydst); hlist_del_init(&policy->bydst_inexact_list); + }
hmask = net->xfrm.policy_bydst[dir].hmask; odst = net->xfrm.policy_bydst[dir].table; - for (i = hmask; i >= 0; i--) - INIT_HLIST_HEAD(odst + i); + for (i = hmask; i >= 0; i--) { + hlist_for_each_entry_safe(policy, n, odst + i, bydst) + hlist_del_rcu(&policy->bydst); + } if ((dir & XFRM_POLICY_MASK) == XFRM_POLICY_OUT) { /* dir out => dst = remote, src = local */ net->xfrm.policy_bydst[dir].dbits4 = rbits4; @@ -1315,8 +1319,6 @@ static void xfrm_hash_rebuild(struct wor chain = policy_hash_bysel(net, &policy->selector, policy->family, dir);
- hlist_del_rcu(&policy->bydst); - if (!chain) { void *p = xfrm_policy_inexact_insert(policy, dir, 0);
--- a/tools/testing/selftests/net/xfrm_policy.sh +++ b/tools/testing/selftests/net/xfrm_policy.sh @@ -257,6 +257,29 @@ check_exceptions() return $lret }
+check_hthresh_repeat() +{ + local log=$1 + i=0 + + for i in $(seq 1 10);do + ip -net ns1 xfrm policy update src e000:0001::0000 dst ff01::0014:0000:0001 dir in tmpl src :: dst :: proto esp mode tunnel priority 100 action allow || break + ip -net ns1 xfrm policy set hthresh6 0 28 || break + + ip -net ns1 xfrm policy update src e000:0001::0000 dst ff01::01 dir in tmpl src :: dst :: proto esp mode tunnel priority 100 action allow || break + ip -net ns1 xfrm policy set hthresh6 0 28 || break + done + + if [ $i -ne 10 ] ;then + echo "FAIL: $log" 1>&2 + ret=1 + return 1 + fi + + echo "PASS: $log" + return 0 +} + #check for needed privileges if [ "$(id -u)" -ne 0 ];then echo "SKIP: Need root privileges" @@ -404,7 +427,9 @@ for n in ns3 ns4;do ip -net $n xfrm policy set hthresh4 32 32 hthresh6 128 128 sleep $((RANDOM%5)) done -check_exceptions "exceptions and block policies after hresh change to normal" +check_exceptions "exceptions and block policies after htresh change to normal" + +check_hthresh_repeat "policies with repeated htresh change"
for i in 1 2 3 4;do ip netns del ns$i;done