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 reference to the to-be-used/dereferenced 'struct sctp_endpoint' (which inherently holds a reference to the problematic 'struct sock') until such a time when we know they 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. This time in inet_sctp_diag_fill().
Cc: Vlad Yasevich vyasevich@gmail.com Cc: Neil Horman nhorman@tuxdriver.com Cc: Marcelo Ricardo Leitner marcelo.leitner@gmail.com Cc: "David S. Miller" davem@davemloft.net Cc: Jakub Kicinski kuba@kernel.org Cc: lksctp developers linux-sctp@vger.kernel.org Cc: "H.P. Yarroll" piggy@acm.org Cc: Karl Knutson karl@athena.chicago.il.us Cc: Jon Grimm jgrimm@us.ibm.com Cc: Xingang Guo xingang.guo@intel.com Cc: Hui Huang hui.huang@nokia.com Cc: Sridhar Samudrala sri@us.ibm.com Cc: Daisy Chang daisyc@us.ibm.com Cc: Ryan Layer rmlayer@us.ibm.com Cc: Kevin Gao kevin.gao@intel.com Cc: linux-sctp@vger.kernel.org Cc: netdev@vger.kernel.org Cc: stable@vger.kernel.org Fixes: 8f840e47f190c ("sctp: add the sctp_diag.c file") Signed-off-by: Lee Jones lee.jones@linaro.org --- net/sctp/diag.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/net/sctp/diag.c b/net/sctp/diag.c index 760b367644c12..998488a56ce2b 100644 --- a/net/sctp/diag.c +++ b/net/sctp/diag.c @@ -292,15 +292,17 @@ static int sctp_tsp_dump_one(struct sctp_transport *tsp, void *p)
static int sctp_sock_dump(struct sctp_transport *tsp, void *p) { - struct sctp_endpoint *ep = tsp->asoc->ep; + struct sctp_endpoint *ep; struct sctp_comm_param *commp = p; - struct sock *sk = ep->base.sk; + struct sock *sk; struct sk_buff *skb = commp->skb; struct netlink_callback *cb = commp->cb; const struct inet_diag_req_v2 *r = commp->r; struct sctp_association *assoc; int err = 0;
+ ep = sctp_endpoint_hold(tsp->asoc->ep); + sk = ep->base.sk; lock_sock(sk); list_for_each_entry(assoc, &ep->asocs, asocs) { if (cb->args[4] < cb->args[1]) @@ -341,6 +343,7 @@ static int sctp_sock_dump(struct sctp_transport *tsp, void *p) cb->args[4] = 0; release: release_sock(sk); + sctp_endpoint_put(ep); return err; }