sctp: check RCV_SHUTDOWN after the sendmsg connect wait

Overview

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

sctp: check RCV_SHUTDOWN after the sendmsg connect wait

sctp_wait_for_connect() drops the socket lock while it sleeps. An out-of-the-blue ABORT can then be processed from the socket backlog and unlink the association. If a concurrent shutdown(fd, SHUT_RD) sets RCV_SHUTDOWN, the waiter breaks with err == 0 before checking asoc->base.dead. Its final sctp_association_put() can then free the association, leaving sctp_sendmsg_to_asoc() to continue with a dangling pointer.

Check RCV_SHUTDOWN along with the wait error in sctp_sendmsg_to_asoc() before using the association again. The check only accesses the socket, so it needs no additional association reference. Return the existing -ESRCH so that sctp_sendmsg() skips freeing a new association that may already have been destroyed.

Keep sctp_wait_for_connect() unchanged to preserve its behavior for the connect() caller.

Affected

• Linux >= 668c9beb9020d5834ee9e43c208190a07d2b1928 < e8f972b1759d26bbefe4c524caae1ed7c8a593bd
• Linux >= 668c9beb9020d5834ee9e43c208190a07d2b1928 < e701345d886e831fb593a0870d69c8c5de6fc938
• Linux >= 668c9beb9020d5834ee9e43c208190a07d2b1928 < 222c41e0f50f1d5028be9baf0e1dcfc0bfa7f669
• Linux >= 668c9beb9020d5834ee9e43c208190a07d2b1928 < 4f1da630d13de0370e2f6361f961f1c8b384af1c
• Linux 4.16

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.