Re: [RESEND 2/2] sctp: hold cached endpoints to prevent possible UAF
flat view
From: Jakub Kicinski <kuba@kernel.org>
Date: 2021-12-16 01:48:24
Also in:
linux-sctp, lkml
On Tue, 14 Dec 2021 21:57:32 +0000 Lee Jones wrote:
The cause of the resultant dump_stack() reported below is a dereference of a freed pointer to 'struct sctp_endpoint' in sctp_sock_dump(). This race condition occurs when a transport is cached into its associated hash table followed by an endpoint/sock migration to a new association in sctp_assoc_migrate() prior to their subsequent use in sctp_diag_dump() which uses sctp_for_each_transport() to walk the hash table calling into sctp_sock_dump() where the dereference occurs. BUG: KASAN: use-after-free in sctp_sock_dump+0xa8/0x438 [sctp_diag] Call trace: dump_backtrace+0x0/0x2dc show_stack+0x20/0x2c dump_stack+0x120/0x144 print_address_description+0x80/0x2f4 __kasan_report+0x174/0x194 kasan_report+0x10/0x18 __asan_load8+0x84/0x8c sctp_sock_dump+0xa8/0x438 [sctp_diag] sctp_for_each_transport+0x1e0/0x26c [sctp] sctp_diag_dump+0x180/0x1f0 [sctp_diag] inet_diag_dump+0x12c/0x168 netlink_dump+0x24c/0x5b8 __netlink_dump_start+0x274/0x2a8 inet_diag_handler_cmd+0x224/0x274 sock_diag_rcv_msg+0x21c/0x230 netlink_rcv_skb+0xe0/0x1bc sock_diag_rcv+0x34/0x48 netlink_unicast+0x3b4/0x430 netlink_sendmsg+0x4f0/0x574 sock_write_iter+0x18c/0x1f0 do_iter_readv_writev+0x230/0x2a8 do_iter_write+0xc8/0x2b4 vfs_writev+0xf8/0x184 do_writev+0xb0/0x1a8 __arm64_sys_writev+0x4c/0x5c el0_svc_common+0x118/0x250 el0_svc_handler+0x3c/0x9c el0_svc+0x8/0xc To prevent this from happening we need to take a references to the to-be-used/dereferenced 'struct sock' and 'struct sctp_endpoint's until such a time when we know it can be safely released. When KASAN is not enabled, a similar, but slightly different NULL pointer derefernce crash occurs later along the thread of execution in inet_sctp_diag_fill() this time.
Are you able to identify where the bug was introduced? Fixes tag would be good to have here. You should squash the two patches together.
quoted hunk ↗ jump to hunk
diff --git a/net/sctp/diag.c b/net/sctp/diag.c index 760b367644c12..2029b240b6f24 100644 --- a/net/sctp/diag.c +++ b/net/sctp/diag.c@@ -301,6 +301,8 @@ static int sctp_sock_dump(struct sctp_transport *tsp, void *p) struct sctp_association *assoc; int err = 0; + sctp_endpoint_hold(ep); + sock_hold(sk); lock_sock(sk); list_for_each_entry(assoc, &ep->asocs, asocs) { if (cb->args[4] < cb->args[1])@@ -341,6 +343,8 @@ static int sctp_sock_dump(struct sctp_transport *tsp, void *p) cb->args[4] = 0; release: release_sock(sk); + sock_put(sk); + sctp_endpoint_put(ep); return err; }