sctp: add a refcnt in sctp_stream_priorities to avoid a nested loop

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: sctp: add a refcnt in sctp_stream_priorities to avoid a nested loop With this refcnt added in sctp_stream_priorities, we don't need to traverse all streams to check if the prio is used by other streams when freeing one stream's prio in sctp_sched_prio_free_sid(). This can avoid a nested loop (up to 65535 * 65535), which may cause a stuck as Ying reported: watchdog: BUG: soft lockup - CPU#23 stuck for 26s! [ksoftirqd/23:136] Call Trace: <TASK> sctp_sched_prio_free_sid+0xab/0x100 [sctp] sctp_stream_free_ext+0x64/0xa0 [sctp] sctp_stream_free+0x31/0x50 [sctp] sctp_association_free+0xa5/0x200 [sctp] Note that it doesn't need to use refcount_t type for this counter, as its accessing is always protected under the sock lock. v1->v2: - add a check in sctp_sched_prio_set to avoid the possible prio_head refcnt overflow.

References

• https://git.kernel.org/stable/c/cec326443f01283ef68ea00c06ea073b1835a562
• https://git.kernel.org/stable/c/8ee401f89cdb10f39098c0656d695b2bc4052100
• https://git.kernel.org/stable/c/bf5540cbd20e2dae2c81ab9b31deef41ef147d0a
• https://git.kernel.org/stable/c/03c3a5584a0a29821e59b7834635ce823050caaa
• https://git.kernel.org/stable/c/6d529928ea212127851a2df8c40d822237ca946b
• https://git.kernel.org/stable/c/68ba44639537de6f91fe32783766322d41848127