sctp: clear out_curr if all frag chunks of current msg are pruned

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: sctp: clear out_curr if all frag chunks of current msg are pruned A crash was reported by Zhen Chen: list_del corruption, ffffa035ddf01c18->next is NULL WARNING: CPU: 1 PID: 250682 at lib/list_debug.c:49 __list_del_entry_valid+0x59/0xe0 RIP: 0010:__list_del_entry_valid+0x59/0xe0 Call Trace: sctp_sched_dequeue_common+0x17/0x70 [sctp] sctp_sched_fcfs_dequeue+0x37/0x50 [sctp] sctp_outq_flush_data+0x85/0x360 [sctp] sctp_outq_uncork+0x77/0xa0 [sctp] sctp_cmd_interpreter.constprop.0+0x164/0x1450 [sctp] sctp_side_effects+0x37/0xe0 [sctp] sctp_do_sm+0xd0/0x230 [sctp] sctp_primitive_SEND+0x2f/0x40 [sctp] sctp_sendmsg_to_asoc+0x3fa/0x5c0 [sctp] sctp_sendmsg+0x3d5/0x440 [sctp] sock_sendmsg+0x5b/0x70 and in sctp_sched_fcfs_dequeue() it dequeued a chunk from stream out_curr outq while this outq was empty. Normally stream->out_curr must be set to NULL once all frag chunks of current msg are dequeued, as we can see in sctp_sched_dequeue_done(). However, in sctp_prsctp_prune_unsent() as it is not a proper dequeue, sctp_sched_dequeue_done() is not called to do this. This patch is to fix it by simply setting out_curr to NULL when the last frag chunk of current msg is dequeued from out_curr stream in sctp_prsctp_prune_unsent().

References

• https://git.kernel.org/stable/c/e27458b18b35caee4b27b37a4a9c503b93cae5cc
• https://git.kernel.org/stable/c/2ea600b598dd3e061854dd4dd5b4c815397dfcea
• https://git.kernel.org/stable/c/3eff34e01062ec08fbb45ce2baaaa644550be821
• https://git.kernel.org/stable/c/2f201ae14ae0f91dbf1cffea7bb1e29e81d4d108