CVE-2021-4454

Summary

In the Linux kernel, the following vulnerability has been resolved:

can: j1939: fix errant WARN_ON_ONCE in j1939_session_deactivate

The conclusion "j1939_session_deactivate() should be called with a session ref-count of at least 2" is incorrect. In some concurrent scenarios, j1939_session_deactivate can be called with the session ref-count less than 2. But there is not any problem because it will check the session active state before session putting in j1939_session_deactivate_locked().

Here is the concurrent scenario of the problem reported by syzbot and my reproduction log.

    cpu0                            cpu1
                            j1939_xtp_rx_eoma

j1939_xtp_rx_abort_one j1939_session_get_by_addr [kref == 2] j1939_session_get_by_addr [kref == 3] j1939_session_deactivate [kref == 2] j1939_session_put [kref == 1] j1939_session_completed j1939_session_deactivate WARN_ON_ONCE(kref < 2)

===================================================== WARNING: CPU: 1 PID: 21 at net/can/j1939/transport.c:1088 j1939_session_deactivate+0x5f/0x70 CPU: 1 PID: 21 Comm: ksoftirqd/1 Not tainted 5.14.0-rc7+ #32 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1 04/01/2014 RIP: 0010:j1939_session_deactivate+0x5f/0x70 Call Trace: j1939_session_deactivate_activate_next+0x11/0x28 j1939_xtp_rx_eoma+0x12a/0x180 j1939_tp_recv+0x4a2/0x510 j1939_can_recv+0x226/0x380 can_rcv_filter+0xf8/0x220 can_receive+0x102/0x220 ? process_backlog+0xf0/0x2c0 can_rcv+0x53/0xf0 __netif_receive_skb_one_core+0x67/0x90 ? process_backlog+0x97/0x2c0 __netif_receive_skb+0x22/0x80

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/6950df42a03c9ac9290503ced3f371199cb68fa9
• https://git.kernel.org/stable/c/b6d44072117bba057d50f7a2f96e5d070c65926d
• https://git.kernel.org/stable/c/9ab896775f98ff54b68512f345eed178bf961084
• https://git.kernel.org/stable/c/1740a1e45eee65099a92fb502e1e67e63aad277d
• https://git.kernel.org/stable/c/d0553680f94c49bbe0e39eb50d033ba563b4212d

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