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authorXin Long <lucien.xin@gmail.com>2021-12-23 13:04:30 -0500
committerDavid S. Miller <davem@davemloft.net>2021-12-25 17:13:37 +0000
commit5ec7d18d1813a5bead0b495045606c93873aecbb (patch)
treed6929bddd265b41fc2e785ae553cd0edf60beb41 /net/sctp/endpointola.c
parentb45396afa4177f2b1ddfeff7185da733fade1dc3 (diff)
sctp: use call_rcu to free endpoint
This patch is to delay the endpoint free by calling call_rcu() to fix another use-after-free issue in sctp_sock_dump(): BUG: KASAN: use-after-free in __lock_acquire+0x36d9/0x4c20 Call Trace: __lock_acquire+0x36d9/0x4c20 kernel/locking/lockdep.c:3218 lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3844 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline] _raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:168 spin_lock_bh include/linux/spinlock.h:334 [inline] __lock_sock+0x203/0x350 net/core/sock.c:2253 lock_sock_nested+0xfe/0x120 net/core/sock.c:2774 lock_sock include/net/sock.h:1492 [inline] sctp_sock_dump+0x122/0xb20 net/sctp/diag.c:324 sctp_for_each_transport+0x2b5/0x370 net/sctp/socket.c:5091 sctp_diag_dump+0x3ac/0x660 net/sctp/diag.c:527 __inet_diag_dump+0xa8/0x140 net/ipv4/inet_diag.c:1049 inet_diag_dump+0x9b/0x110 net/ipv4/inet_diag.c:1065 netlink_dump+0x606/0x1080 net/netlink/af_netlink.c:2244 __netlink_dump_start+0x59a/0x7c0 net/netlink/af_netlink.c:2352 netlink_dump_start include/linux/netlink.h:216 [inline] inet_diag_handler_cmd+0x2ce/0x3f0 net/ipv4/inet_diag.c:1170 __sock_diag_cmd net/core/sock_diag.c:232 [inline] sock_diag_rcv_msg+0x31d/0x410 net/core/sock_diag.c:263 netlink_rcv_skb+0x172/0x440 net/netlink/af_netlink.c:2477 sock_diag_rcv+0x2a/0x40 net/core/sock_diag.c:274 This issue occurs when asoc is peeled off and the old sk is freed after getting it by asoc->base.sk and before calling lock_sock(sk). To prevent the sk free, as a holder of the sk, ep should be alive when calling lock_sock(). This patch uses call_rcu() and moves sock_put and ep free into sctp_endpoint_destroy_rcu(), so that it's safe to try to hold the ep under rcu_read_lock in sctp_transport_traverse_process(). If sctp_endpoint_hold() returns true, it means this ep is still alive and we have held it and can continue to dump it; If it returns false, it means this ep is dead and can be freed after rcu_read_unlock, and we should skip it. In sctp_sock_dump(), after locking the sk, if this ep is different from tsp->asoc->ep, it means during this dumping, this asoc was peeled off before calling lock_sock(), and the sk should be skipped; If this ep is the same with tsp->asoc->ep, it means no peeloff happens on this asoc, and due to lock_sock, no peeloff will happen either until release_sock. Note that delaying endpoint free won't delay the port release, as the port release happens in sctp_endpoint_destroy() before calling call_rcu(). Also, freeing endpoint by call_rcu() makes it safe to access the sk by asoc->base.sk in sctp_assocs_seq_show() and sctp_rcv(). Thanks Jones to bring this issue up. v1->v2: - improve the changelog. - add kfree(ep) into sctp_endpoint_destroy_rcu(), as Jakub noticed. Reported-by: syzbot+9276d76e83e3bcde6c99@syzkaller.appspotmail.com Reported-by: Lee Jones <lee.jones@linaro.org> Fixes: d25adbeb0cdb ("sctp: fix an use-after-free issue in sctp_sock_dump") Signed-off-by: Xin Long <lucien.xin@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/sctp/endpointola.c')
-rw-r--r--net/sctp/endpointola.c23
1 files changed, 15 insertions, 8 deletions
diff --git a/net/sctp/endpointola.c b/net/sctp/endpointola.c
index 48c9c2c7602f..efffde7f2328 100644
--- a/net/sctp/endpointola.c
+++ b/net/sctp/endpointola.c
@@ -184,6 +184,18 @@ void sctp_endpoint_free(struct sctp_endpoint *ep)
}
/* Final destructor for endpoint. */
+static void sctp_endpoint_destroy_rcu(struct rcu_head *head)
+{
+ struct sctp_endpoint *ep = container_of(head, struct sctp_endpoint, rcu);
+ struct sock *sk = ep->base.sk;
+
+ sctp_sk(sk)->ep = NULL;
+ sock_put(sk);
+
+ kfree(ep);
+ SCTP_DBG_OBJCNT_DEC(ep);
+}
+
static void sctp_endpoint_destroy(struct sctp_endpoint *ep)
{
struct sock *sk;
@@ -213,18 +225,13 @@ static void sctp_endpoint_destroy(struct sctp_endpoint *ep)
if (sctp_sk(sk)->bind_hash)
sctp_put_port(sk);
- sctp_sk(sk)->ep = NULL;
- /* Give up our hold on the sock */
- sock_put(sk);
-
- kfree(ep);
- SCTP_DBG_OBJCNT_DEC(ep);
+ call_rcu(&ep->rcu, sctp_endpoint_destroy_rcu);
}
/* Hold a reference to an endpoint. */
-void sctp_endpoint_hold(struct sctp_endpoint *ep)
+int sctp_endpoint_hold(struct sctp_endpoint *ep)
{
- refcount_inc(&ep->base.refcnt);
+ return refcount_inc_not_zero(&ep->base.refcnt);
}
/* Release a reference to an endpoint and clean up if there are