CVE-2022-49838

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().

A kernel crash was triggered by an inconsistency in the SCTP stream scheduler, where out_curr was not cleared when all fragmented chunks of a message were pruned (not properly dequeued). This led to a use-after-free scenario during subsequent stream scheduling operations, causing memory corruption and a kernel panic. This issue requires the ability to send SCTP messages with PR-SCTP (Partial Reliability) and fragmented data, which is typically restricted to privileged users or those running SCTP-capable applications on controlled environments.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.