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There is a race condition between a thread calling bt_accept_dequeue() and a different thread calling bt_accept_unlink(). Protection against concurrency is implemented using sk locking. However, sk locking causes serialisation of the bt_accept_dequeue() and bt_accept_unlink() threads. This serialisation can cause bt_accept_dequeue() to obtain the sk from the parent list but becomes blocked waiting for the sk lock held by the bt_accept_unlink() thread. bt_accept_unlink() unlinks sk and this thread releases the sk lock unblocking bt_accept_dequeue() which potentially runs bt_accept_unlink() again on the same sk causing a crash. The attempt to double unlink the same sk from the parent list can cause a NULL pointer dereference crash due to bt_sk(sk)->parent becoming NULL on the first unlink, followed by the second unlink trying to execute bt_sk(sk)->parent->sk_ack_backlog-- in bt_accept_unlink() which crashes. When sk is in the parent list, bt_sk(sk)->parent will be not be NULL. When sk is removed from the parent list, bt_sk(sk)->parent is set to NULL. Therefore, add a defensive check for bt_sk(sk)->parent not being NULL to ensure that sk is still in the parent list after the sk lock has been taken in bt_accept_dequeue(). If bt_sk(sk)->parent is detected as being NULL then restart the loop so that the loop variables are refreshed to use the latest values. This is necessary as list_for_each_entry_safe() is not thread safe so causing a risk of an infinite loop occurring as sk could point to itself. In addition, in bt_accept_dequeue() increase the sk reference count to protect against early freeing of sk. Early freeing can be possible if the bt_accept_unlink() thread calls l2cap_sock_kill() or rfcomm_sock_kill() functions before bt_accept_dequeue() gets the sk lock. For test purposes, the probability of failure can be increased by putting a msleep of 1 second in bt_accept_dequeue() between getting the sk and waiting for the sk lock. This exposes the fact that the loop list_for_each_entry_safe(p, n, &bt_sk(parent)->accept_q) is not safe from threads that unlink sk from the list in parallel with the loop which can cause sk to become stale within the loop. Signed-off-by: Dean Jenkins <Dean_Jenkins@mentor.com> Signed-off-by: Marcel Holtmann <marcel@holtmann.org> |
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| .. | ||
| bnep | ||
| cmtp | ||
| hidp | ||
| rfcomm | ||
| 6lowpan.c | ||
| a2mp.c | ||
| a2mp.h | ||
| af_bluetooth.c | ||
| amp.c | ||
| amp.h | ||
| ecc.c | ||
| ecc.h | ||
| hci_conn.c | ||
| hci_core.c | ||
| hci_debugfs.c | ||
| hci_debugfs.h | ||
| hci_event.c | ||
| hci_request.c | ||
| hci_request.h | ||
| hci_sock.c | ||
| hci_sysfs.c | ||
| Kconfig | ||
| l2cap_core.c | ||
| l2cap_sock.c | ||
| leds.c | ||
| leds.h | ||
| lib.c | ||
| Makefile | ||
| mgmt_util.c | ||
| mgmt_util.h | ||
| mgmt.c | ||
| sco.c | ||
| selftest.c | ||
| selftest.h | ||
| smp.c | ||
| smp.h | ||